Van Lishout, Jan August (Kontich, BE)
Jaeken, Jan (Hove, BE)

04/852236

03/20/1973

08/22/1969

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Agfa-Gevaert N.V. (Mortsel, BE)

430/365

430/363, 430/376

G03C1/46; G03C1/485; G03C5/16; G03C7/18; G03C7/28; G03C7/333; G03C7/34; G03C8/04; G03C8/16; G03C8/02; G03C1/76; G03C7/00

96/54,100,74,68,69 250/65

3222176	Photographic colour images from amino substituted phenols	December 1965	Jaeken
3351466	Radiographs viewable by reflected or transmitted light	November 1967	Land

Torchin, Norman G.

Fichter, Richard E.

We claim

1. A method of producing a colored radiograph which comprises the steps of:

2. image-wise exposing to directly or indirectly recordable penetrating radiation a photographic material comprising at least one silver halide emulsion layer containing silver chloride in an amount corresponding with 5 to 16 g of silver nitrate per sq.m and a colorless color coupler which forms an azomethine- or quinonimine dyestuff by coupling with an oxidized p-phenylene diamine type developing agent and a colorless hydrazone compound having the formula

3. color developing the exposed silver halide with a p-phenylene diamine type developing agent to produce in the exposed areas of said emulsion layer an image of said azomethine or quinonimine dyestuff, and

4. removing the silver metal produced during said development with an alkaline oxidizing bleaching solution effecting the oxidative coupling of said hydrazone compound with said colorless color coupler left in the unexposed areas, said color coupler and hydrazone compound being adapted upon such coupling to form a dye image of substantially contrasting color and opposite gradation to the first developed dye image.

5. A method of producing a colored radiograph according to claim 1 wherein the colorless color coupler is a phenol, -naphthol or 3-pyrazoline-5-one type color coupler.

6. A method of producing a colored radiograph according to claim 2 wherein the phenol coupler has the following general formula: ##SPC32##

7. A method of producing a colored radiograph according to claim 1 wherein said colorless color coupler and said hydrazone compound are present in sufficient amounts to produce a dye image of contrasting color and opposite gradation having a density equal to at least 50 percent of the maximum density of the main color of said azomethine or quinonimine dyestuff image.

The present invention relates to a method for producing color radiographs having an improved information content in comparison with black-and-white radiographs.

It is known to improve the discernability of the details of radiographs, i.e., photographic images produced directly or indirectly by means of penetrating rays, e.g., γ-rays, X-rays and other highly energetic radiation, by adding to differences in brightness, differences in color saturation and hue.

An extensive review of known techniques for producing colored radiographs is given by Dr.-Ing. H.V.Richter and Pruf.-Ing.D.Linke in the article : "Grundlagen und Verfahren der Color-Radiographie," (Die Technik, Vol. 21, no. 7/66, pages 424-431).

It is one of the objects of the present invention to provide a method for the production of color radiographs that have an excellent contrast and a higher discernability of the details of the image to be produced than have black-and-white radiographs produced according to methods known hitherto.

According to the present invention in a recording material comprising one or more silver halide emulsions a developable latent silver image is formed by means of directly or indirectly recorded penetrating radiation and is processed in such a way that at least two images of contrasting color and of opposite gradation are obtained.

The recording by means of penetrating radiation includes a direct as well as an indirect exposure. The indirect exposure is an exposure to visible and/or U.V. light produced by converting penetrating radiation, i.e., high energetic radiation such as X-rays, alpha, beta or gamma rays and neutrons suited for making radiographs, into visible and/or U.V. light and/or electrons obtained as a secondary emission from e.g., lead screens. The indirect exposure can be a "screen-exposure" wherein penetrating radiation is used, which is projected and converted into visible light and/or U.V. light on a fluorescing screen.

The recording includes all types of exposure with radiation that produces a latent silver image, e.g., simultaneous exposure to a pattern of such radiation, and also scanning-wise exposure e.g., by means of a light spot that is modulated according to the radiographic information to be recorded.

The term "contrasting colors" used in the present invention points to colors that visually markedly differ from each other, e.g., blue and red, red and yellow, red and green, black and yellow, black and green, black also being considered as a color in the present invention, so that the combination of (a) silver image(s) with (a) color image(s) of opposite gradation is not excluded. Good detail reproduction can be obtained by producing color images in different complementary color pairs e.g., blue and yellow, green and magenta. Mixtures of colors are included, e.g., yellowish green color tones and color tones which lay between yellow and red, to which the human eye is particularly sensitive, can be used too. The legibility of lettering (color of lettering on colored background has been described by Boris Townsend in The British Journal of Photography, Jan. 1969 p. 106 and gives preferred combinations of contrasting colors e.g., black image parts on a yellow background.

If the photographic image is constituted of two color images these need not necessarily be formed in the same layer of a same silver halide photographic material, but may be formed in different layers thereof.

Thus, analogously with conventional radiographic film where both sides of a support are provided with a radiation-sensitive silver halide emulsion layer, the positive and negative color image in the method according to the present invention may be formed at either side of the support of the radiographic film.

The invention also includes the production of a color radiograph wherein two color images are obtained in one or more layers at one side of a support, and one or two of the color images are also obtained at the other side of the support.

The color images of contrasting colors need not be formed in one emulsion layer but may be formed by the superposition of two or more color images, wherein all of them may be either positive or negative, and may be obtained in several layers. E.g., a red positive image may be constituted of a yellow positive image produced in one layer and of a magenta positive image produced in an other layer either adjacent to the first layer or remote therefrom, e.g., at the other side of the support.

According to a preferred embodiment two color images of opposite gradation, in other words a negative and a positive color image, are produced in the same recording material and more preferably in the same silver halide emulsion layer.

According to the present invention wherein color images of opposite gradation are produced, one color of the radiographic image obtained may mainly stress variations in the higher densities. Thus, the sensitometric characteristics of the positive image may differ from those of the negative image.

For instance, the contrast of the positive image may be softer or harder than that of the negative image, or the sensitivity of the silver halide emulsion layer(s) wherein one image is produced may differ from that of the layer(s) wherein the other image is formed.

The mentioned differences in the sensitometric properties may be obtained by a particular processing of a standard type silver halide emulsion layer or layer system or by a common processing of a film with (a) particularly composed silver halide emulsion layer(s).

The recognition of density differences in the lower and the higher densities may be improved by viewing or projecting the radiographic image by means of colored light (e.g. using a color filter set in combination with white light) to obtain a hue, the contrast of which is low in respect of one color image and high in respect of the other.

Several recording and processing systems based on the use of light-sensitive silver halide can be applied as such or in a modified way to produce a combination of a positive and negative color image in the same recording material.

Thus, it is known to produce a negative and positive color image of opposite gradation for the purpose of masking. Photographic masking may be described as a modification of the density distribution of a negative by the combination in register with a positive image having a gradation opposite to that of the negative image.

Many different masking processes have been proposed among which masking processes known under the term "integral masking" have become of particular interest. For a survey of such processes reference is made to Bernhard Morcher, Photo-Technik und -Wirtschaft, No. 8 (1966) p.348-350.

According to the present invention said integral masking process can be modified in such a way that negative and positive color images are obtained wherein the positive color image has a density substantially higher than is necessary for compensating the side absorptions of the negative color image.

Preferably according to the present invention the maximum density of the image of opposite gradation (in integral masking, called the masking image, and here the secondary image) is as high as or amounts to at least 50 percent of the maximum density of the main color of the primary color image. This can be realized with either of the existing integral masking systems by adapting the concentration of the proper compounds and the processing for producing the color image of opposite gradation.

According to a first technique derived from an integral masking process (see e.g., U.K. Patent Specification No. 599,377 filed Oct. 7, 1944 by Kodak and corresponding U.S. Pat. specification No. 2,499,996 of Wesley T.Hanson, Jr. issued Sept. 21, 1948 two color images of opposite gradation are formed in one and the same silver halide emulsion layer containing colored color couplers. According to the present invention said silver halide emulsion preferably contains the colored color couplers in such a concentration that in the areas, wherein by color development after "direct" or "indirect" exposure to said penetrating radiation no primary image has been formed, sufficiently colored color coupler is left to obtain a secondary image the maximum density of which is higher than that normally obtained in masking procedures for compensating the influence of the densities of the side absorption(s) of the primary color image.

It has to be noticed that for the purpose of the present invention no cyan, magenta or yellow primary images must be formed as is required for the formation of a multicolor image according to the principles of subtractive color photography. Indeed, the color of the primary image is only so far important as it contrasts with the color of the secondary image. So, according to a preferred embodiment of the present invention a blue negative image is produced by means of a yellow colored color coupler forming the positive image.

Further it has to be noticed that it is not necessary for the primary image to be a negative image in respect of the original since for the purpose of the present invention a silver halide emulsion of the direct-positive type can be used just as well. Such silver halide emulsions can produce a direct-positive silver image e.g., according to the Herschel or solarization effect.

According to a preferred embodiment of the present invention a negative image (primary image) is formed by means of a color coupler suited for forming a quinonimine or azomethine dye on color development of the exposed silver halide with an aromatic primary amino developing agent and a positive image (secondary image) is obtained by oxidation of a compound or oxidative copulation of a compound with color coupler being residual after color development.

So, according to a second technique contrasting color images of opposite gradation can be produced along the steps of an integral masking process wherein the secondary image is produced by the oxidative coupling of a colorless compound called "masking compound" with a colorless coupler left in the unexposed areas. Suitably oxidatively coupling compounds are 4-amino-pyrazolones described in the U.K. Pat. specifications Nos. 880,862 filed Dec. 31, 1956 and 975,930 filed June 27, 1961 both by Gevaert Photo-Producten N.V. and in the U.S. Pat. specs. Nos. 3,012,884 and 3,013,879 both of Maurice Antoine de Ramaix and Jan Jaeken issued Dec. 12, 1961 and issued Dec. 19, 1961.

More particularly 4-aminopyrazolones are meant corresponding to the following general formula: ##SPC1##

wherein :

R ₁ represents an alkyl group of at most five carbon atoms,

R ₂ represents an alkyl group of at most five carbon atoms, a phenyl group or a substituted phenyl group, and

R ₃ represents an alkyl group of more than five carbon atoms which inhibits migration in colloid layers of the compound involved.

Other suitable oxidatively coupling compounds are p-phenylene-diamines with sterically hindered amino group as described e.g., in the published U.K. Pat. specification No. 1,153,561 filed Jan. 18, 1966 by Gevaert-Agfa N.V.

More particularly are used p-phenylenediamine derivatives corresponding to the following general formula :

wherein :

R ₁ represents a hydrogen atom, a monovalent organic group, or an organic bivalent group linked to an ortho-atom of the aromatic group represented by A,

R ₂ represents a monovalent organic group, or a bivalent organic group linked to an ortho-atom of the aromatic group represented by A, or

R ₁ together with R ₂ forms a nitrogen-containing nucleus including a substituted nucleus,

A represents an aromatic group, which in the p-position to the

is substituted by the --NH--R ₃ group, and in the o-positions in respect of the --NH--R ₃ group is substituted with a halogen atom, an alkyl group, an alkoxy group, a cyano group, an acyl group, an acyl-substituted amino group, a sulphamyl group, an alkylsulphonyl group, an arylsulphonyl group, a sulpho group or a carboxylic group in acid or salt form, A including such an aromatic group which is further substituted.

Other suitably oxidatively coupling compounds are sterically hindered phenols described in the French Pat. specification No. 1,508,682 filed Jan. 17, 1967 by Gevaert-Agfa N.V. the U.K. Pat. specification No. 975,940 filed Nov. 30, 1959 by Gevaert Photo-Producten N.V. and the U.S. Pat. specification No. 3,047,385 of Maurice Antoine de Ramaix and Jan Jaeken issued July 31, 1962.

Particularly useful sterically hindered phenols are within the scope of the following general formula : ##SPC2##

wherein :

each of R ₁ and R ₂ represents a sterically hindering group selected from the group consisting of tert.-butyl, cyclohexyl and phenyl, and

R ₃ represents a member selected from the group consisting of a hydrogen atom, a halogen atom and a radical which is sufficiently unstable for being split off on treatment with an oxidizing photographic bleaching bath.

Particularly useful oxidatively coupling compounds are further hydrazones capable of producing azine compounds by oxidative copulation with aromatic hydroxy compounds, e.g., phenols and naphthols and 2 -pyrazoline-5-one compounds. Compounds having such copulation ability contain the amidrazone system or a vinylog thereof represented by :

Particularly suited compounds for application in such a process are described e.g., in the U.K. Pat. specification Nos. 975,932 filed Nov. 13, 1959, 993,749 filed June 30, 1962 and 995,798 filed May 4, 1962 all by Gevaert Photo-Producten N.V., in the U.S. Pat. spec. No. 3,245,787, of Jozef Frans Willems and Jan Jaeken issued Apr. 12, 1966, U.S. Pat. No. 3,245,788 of Jan Jaeken and Robert Leopold Janseune issued April 12, 1966 and U.S. Pat. No. 3,310,402 of Jan Jaeken and Hugo Vital Van Goethem issued Mar. 21, 1967 and in the published Dutch Patent application No. 6712657 filed Sept. 15, 1967 by Gevaert-Agfa N.V.

Preferably used hydrazone compounds contain a grouping of the following structure :

wherein :

R ₂ represents a group of the formula --CONH ₂ or --SO ₂ X wherein X represents a hydroxyl, an amino or a substituted amino group, a heterocyclic group, an alkyl or a substituted alkyl group, an aryl or a substituted aryl group,

R ₃ represents a hydrogen atom, an alkyl group, an allyl group, an aralkyl group, an aryl group or a substituted aryl group,

L ₂ represents a methine group or a nitrogen atom, and

n is a positive integer from 1 to 2.

Preferred hydrazone compounds correspond to the following general formulas :

wherein :

R ₁ is a member of the group consisting of a hydrogen atom and an acetyl group,

R ₂ is a member of the group consisting of an alkyl radical and an aryl radical,

Z represents the non-metallic atoms necessary to complete a heterocyclic nucleus containing 5-6 members, at least one of which is a nitrogen atom, and

X is a member of the group consisting of an hydroxyl radical, an amino radical, an alkyl radical, an aryl radical, and a heterocyclic radical;

wherein :

R ₁ is a member of the group consisting of a hydrogen atom and an acyl radical,

Y represents the non-metallic atoms necessary to complete a nitrogen-containing heterocyclic nucleus,

R ₂ is a member of the group consisting of a hydrogen atom, an amino radical, an alkyl radical, an alkylene radical, an aryl radical, and a heterocyclic radical, and

X is a member of the group consisting of an hydroxyl radical, an amino radical, an aliphatic hydrocarbon radical, an aryl radical, and a heterocyclic radical.

For the purpose of the present invention the masking compounds are preferably used in an amount substantially higher than is necessary for producing a masking image compensating for the side-absorptions of the primary color image.

The preferred masking compounds are those that may be incorporated into the silver halide emulsion without causing fog. In that respect hydrazone compounds are mentioned, which contain the structural group

wherein R represents a sulphonic acid group, an acyl group or an amide group, e.g., a sulphonylalkyl group, a sulphonylaryl group, a --CONH ₂ group or a --SO ₂ NH ₂ group including these groups in substituted form.

It has to be noticed, that the masking compound and color coupler need not to be incorporated in diffusion-resistant form into the silver halide emulsion but may be introduced therein during the processing from a developing bath. The oxidative copulation of the masking compound with the color coupler proceeds very well in a conventional alkaline photographic bleaching bath.

According to a third technique derived from still another integral masking process, the secondary image is produced independently from the color couplers used for the formation of the primary color image. Said masking technique and suitable compounds therefor are described in the German Pat. specification No. 1,083,125 filed Dec. 11, 1958 by Agfa A.G., the U.K. Pat. specification No. 916,657 filed Dec. 11, 1959 by Agfa A.G. and the U.S. Pat. spec. No. 3,186,840 of Walter Puschel, Ottmar Wahl, Willibald Pelz, Hans Schellenberger and Karl Loffler issued June 1, 1965 and U.S. Pat. No. 3,378,554 of Walter Puschel, Hans Schellenberger, Karl Loffler, Ottmar Wahl and Willibald Pelz issued Apr. 16, 1968.

According to said technique a silver halide emulsion is used comprising (a) color coupler(s) and a colorless dihydrazone compound containing the structural group

and which is capable of coupling with the oxidation product of the color developing agent(s) so as to form a colorless copulation product. Due to this property, the said colorless dihydrazone coupler stands in competition with the color coupler in the reaction with the oxidized developing agent. In the unexposed areas the non-reacted dihydrazone is oxidized in the photographic bleaching bath and forms a product having the required color for compensating the side absorption(s) of the primary color image. The system as described e.g., in the said U.K. Pat. specification No. 916,657 and U.S. Pat. spec. Nos. 3,186,840 and 3,378,554 is particularly useful for producing a yellow secondary image. The system may be modified for the purpose of the present invention, e.g., by producing as primary image a blue image and as secondary image a yellow image. Preferably the color coupler and the colorless dihydrazone are incorporated into separate silver halide emulsion layers so that difficulties arising from differences in velocity of copulation of the oxidized developing agent with said dihydrazone and said color coupler respectively can be kept under control more easily.

A preferred photographic material suited for use according to the present invention contains a color coupler or mixture of color couplers by means of which on color development with an aromatic primary amino developing agent a primary dye image is formed, which absorbs in the red region (700-600 nm) of the visible spectrum and also in the green region (600-500 nm) for at least 30 percent in respect of the red region. Such a material also contains another compound e.g., a said hydrazone compound by means of which in the photographic bleaching bath a secondary dye image contrasting in color to the primary dye image and having a gradation opposite to that of the primary dye image is formed.

Preferably the absorption in the blue region (400-500 nm) of the primary dye image at 450 nm is not higher than the maximum absorption in the green region of the spectrum.

The primary dye image having the above described absorption characteristics can be formed by means of a mixture of cyan- and magenta-forming couplers or a single coupler producing on copulation with the oxidation product of an aromatic primary amino developing agent e.g., a p-phenylenediamine derivative a dye absorbing in the red and green regions as indicated.

Phenol couplers that are suited for producing a blue dye image or dye images having a main absorption in the red region of the visible spectrum and considerable (more than 30 percent side-absorption absorption in the green correspond to the following general formula : ##SPC3##

wherein :

R represents a carboxylic acid acyl or sulphonic acid acyl group including said groups in substituted state, e.g., an aliphatic carboxylic acid acyl group, an aromatic carboxylic acid acyl group, an heterocyclic carboxylic acid acyl group, e.g., a 2-furoyl group or a 2-thienoyl group, an aliphatic sulphonic acid acyl group, an aromatic sulphonic acid acyl group, a sulphonylthienyl group, an aryloxy-substituted aliphatic carboxylic acid acyl group, a phenylcarbamyl aliphatic carboxylic acid acyl group, or a tolyl carboxylic acid acyl group.

For such type of color couplers and their preparation reference may be made, e.g., to the U.S. Pat. spec. No. 2,772,162 of Ilmari F.Salminen and Charles R.Barr issued Nov. 27, 1956 and U.S. Pat. No. 3,222,176 of Jan Jaeken issued Dec. 7, 1965, and to the U.K. Pat. specification No. 975,773 filed Sept. 4, 1961 by Gevaert Photo-Producten N.V.

The problem of producing a negative and positive image of contrasting color tone in one and the same recording material can be solved in still other ways than according to the principles of integral masking.

So, for the purpose of the present invention silver halide recording materials can be used that contain two silver halide emulsions wherein a negative and a positive image are produced respectively.

For the production of said negative of said negative or positive images known emulsion types and processing techniques may be applied.

The production of negative color images proceeds preferably according to the generally known technique of a color forming development reaction by mean of color couplers as described e.g., by W.A. Schmidt Vsevolod Tulagin, J.S.Sprung, R.C. Gunther, R.F.Coles, and D.E.Sargent in Ind.Eng.Chem. (Aug. 1953), p. 1726-1729.

The production of positive color images may proceed according to a great variety of techniques a short survey of which is given hereinafter without the intention of limitation.

A first technique is based on the local destruction of dyes in contact with a silver image. The principles of such method and practically useful embodiments are described by P.Glafkides in Photographic Chemistry, Vol. II (1960) p. 643-646 and in the published Dutch Patent application No. 6610353 filed July 22, 1966 by Gevaert-Agfa N.V.

In the so-called silver dye bleach process preferably azodyes are used as bleachable compounds, e.g., the dyes Diamine Pure Blue FF, Mordant Yellow GG, Diamine Fast Pink BBF, Chrysophenine G, and Superanol Brilliant Red 3B in a concentration of 0.6 to 0.8 g per sq.m.

The azodyes are much more stable to light and heat than the azomethine, and quinoneimine dyes of the negative color process. The destruction may be activated by bromide ions or thiourea, and is considerably accelerated by the combined use of thiourea and catalysts known as azines.

The following compounds are useful representatives of the latter class : ##SPC4##

The third compound is preferably added to the black-and-white developing composition so that it is already present in the emulsion layer at the moment of bleaching.

Although the silver dye bleach process is mainly intended for producing a positive color image starting from a negative silver image, it can be applied equally well in a method wherein in respect of the original a positive silver image is produced, e.g., according to a process known as a black-and-white reversal processing, e.g., as described in the U.S. Pat. specification No. 2,759,824 of Ralph B.Atkinson issued Aug. 21, 1956, or by application of the bromide ion diffusion process described, e.g., in the U.K. Pat. specifications No. 690,997 filed Oct. 21, 1949 by Farbenfabriken Bayer and 753,189 filed Sept. 14, 1954 by Agfa A.G. and the published German Pat. application No. 1,181,055 filed July 12, 1963 by Agfa A.G.

A positive black-and-white silver image may also be produced by the photographic process known as "photosolubilization process" described, e.g., in the U.S. Patent specifications Nos. 3,155,506 - 3,155,507 - 3,155,514 - 3,155,516 - 3,155,517 - 3,155,518 and 3,155,519 all of Ralph Kingsley Blake, issued Nov. 3, 1964.

A direct-positive silver image, which is applicable e.g., to silver dye bleaching can be produced by means of special silver halide emulsions that are described e.g., in the published U.K. Pat. specifications No. 1,151,363 filed Apr. 30, 1965 and 1,150,553 filed Apr. 30, 1965 both by Gevaert-Agfa N.V., and the French Pat. specifications 1,541,559 and 1,541,561 both filed Oct. 23, 1967 by Gevaert-Agfa N.V.

The silver halide emulsions used in that direct-positive process are of the type wherein mainly an internal latent image and to a minor extent external latent image is formed. Such special silver halide emulsions are generally not or only slightly chemically ripened silver halide emulsions, since the ability of forming surface latent image increases with the degree of chemical ripening.

Silver chlorobromide emulsions comprising at least 20 mol. percent of silver bromide and pure silver bromide emulsions have proved to be very suitable. When these emulsions comprise a certain amount of silver iodide, often not more than 5 mole percent relative to the total amount of silver halide, they are just as well suitable. Washed as well as unwashed silver halide emulsions may be used.

As already has been explained the information-wise exposure may be either a direct or indirect exposure.

The exposed recording material is developed with an energetic surface developer, e.g., by conducting the material through a tray containing such developer, by means of a lick-roller, by spraying or by rubbing. The developer may be more or less viscous. It must be a surface developer, i.e., a developer that contains no or at least no effective amount of solvents for silver halide. By the expression "solvents for silver halide" particularly strong solvents for silver halide such as water-soluble thiocyanates, thiosulphates, ammonia, etc. are meant. Indeed, compounds, that may be considered as but very weak solvents for silver halide, such as sodium sulphite for the case the silver halide is silver bromide, silver chlorobromide or silver bromoiodide, may be present in the developer.

According to a first embodiment the light-sensitive material is exposed uniformly to actinic light of low intensity while the image-wise exposed light-sensitive layer is present in the developer or is moistened therewith in some other way. This overall exposure may begin simultaneously with the treatment of the light-sensitive material with developer but preferably occurs somewhat later, e.g., from 5 to 30 seconds later. The duration of the said secondary or overall exposure is not very critical and may vary between 10 seconds and several minutes according to the nature of the light-sensitive material, the composition and the temperature of the developer, the intensity of the light-source employed, etc. In many cases the said overall exposure lasts as long as the development. This offers the additional advantage that one can follow the development and stop it when the direct positive image is thought to have reached a sufficient density.

The density of the direct positive image can be made more intense or be reduced locally during the said second or overall exposure by the well known technique of burning in and dodging. The uniformity of said overall exposure to actinic light of low intensity is mostly achieved by interposing between the light-source and the light-sensitive material to be exposed a light-diffusing member that transmits at least part of the light rays of the spectral region to which the light-sensitive material is sensitive. The required low intensity of the light rays, which reach the light-sensitive material, can be obtained by adapting the light-source and/or the light-diffusing member.

According to a second embodiment instead of or in addition to the overall exposure, at least one fogging agent selected from hydrazine, carbazic acid, bicarbamic ac id and/or at least one water-soluble salt thereof may be added to the energetic surface developer and/or to a preceding processing liquid for the light-sensitive recording material. These fogging agents cause the formation of a latent direct-positive image that will be developable by the energetic surface developer. The best results are obtained with the fogging agent(s) added to the developer itself. When using in this embodiment of the present invention another processing liquid incorporating the fogging agent(s), this liquid is preferably employed just before the development step. The pH of the liquid to which the fogging agent has been added is preferably fairly high and in most cases amounts to at least about 10. A preceding separate processing liquid containing the fogging agent(s) may comprise other ingredients such as one or more of the ingredients that otherwise are incorporated into the developer.

Usually the fogging agent is added to the processing liquid in an amount varying between about 1 g and about 50 g, preferably between 5 g and 20 g per liter.

In general a sufficient development of the direct positive image does not take much time and in most cases can be carried out in from 10 to 60 seconds.

The maximum density of the direct positive image may be increased by carrying out the development in the presence of a compound setting free iodide ions in an aqueous medium and/or a compound setting free bromide ions in an aqueous medium. Especially water-soluble iodides such as potassium iodide, are very suited for this purpose.

The minimum density of the direct positive image can be lowered by incorporating a fog-inhibiting compound into the light-sensitive recording material. This fog-inhibiting compound must be present in effective contact with the silver halide emulsion layer. By "in effective contact" is meant that the fog-inhibiting compound is provided in the light-sensitive recording material on a place from which it can act upon the silver halide emulsion layer at the appropriate moment, in this case during the soaking of the light-sensitive material with the developer. The fog-inhibiting compound is preferably incorporated into the silver halide emulsion layer itself, but may also be present in an other water-permeable non-light-sensitive layer of the light-sensitive material such as a covering layer or an intermediate layer, from which it is dissolved by the developer liquid and diffuses to the light-sensitive layer. It is even possible to incorporate considerable amounts of the fog-inhibiting compound into the developer liquid.

The fog-inhibiting compounds give rise to a lowering of the minimum density of the direct-positive image even when present only in small amounts. They are sufficiently efficient when applied in the common fog-inhibiting amounts. The best results i.e., the most clear minimum densities are attained, however, when using the fog-inhibiting compounds in amounts larger than the common fog-inhibiting amounts i.e., in amounts that normally are not applied to light-sensitive materials since they would desensitize the light-sensitive material too much. Suprisingly, these large amounts of fog-inhibiting compound do not lower the direct-positive image sensitivity of the light-sensitive recording material but in most cases even enhance it and also do not prevent the formation of a direct-positive image with good maximum density. Specific data about the concentrations in which the fog-inhibiting compounds are generally employed and yield optimal results can hardly be given since according to the nature of the fog-inhibiting compound and the kind of silver halide emulsion layer used they are widely divergent.

As a variant on the latter direct positive black-and-white process a photographic direct positive color image may be produced by a process including the following steps : imagewise exposing a recording material containing a light-sensitive silver halide wherein mainly internal latent image and little external latent image is formed, developing the light-sensitive material thus exposed with an energetic surface developer in the presence of a color coupler forming a dye with the oxidized developing agent, and overall-exposing the light-sensitive material during the developing stage to actinic light of low intensity, and/or carrying out the said development in the presence of a suitable fogging agent.

Further in the survey of direct positive color reproduction reference is made to a process wherein use is made of colored or colorless compounds, which react with the oxidized developing substances forming colorless compounds or dyes which can be easily bleached in acid medium and which react in an oxidative alkaline solution with another colorless compound to form acid-resistant dyes. Such process is described, e.g., in the U.K. Pat. specification No. 990,628 filed Aug. 2, 1961 by Gevaert Photo-Producten N.V., the published Dutch Pat. application No. 6509590 filed July 23, 1965 by Gevaert-Agfa N.V., and the U.S. Pat. spec. No. 3,293,032 of Jan Jaeken and Maurice Antoine de Ramaix issued Dec. 20, 1966.

The production of photographic reversal color images according to an embodiment of that process includes the steps of :

1. image-wise exposing a photographic element comprising at least one water-permeable layer which contains radiation sensitive silver halide grains, in effective contact with these grains a color coupler capable of forming on development an azomethine or quinoneimine dye which by treatment with an acidic solution, the hydrogen ion concentration of which is at least 10 ^-1 gram-equivalent per liter, can be transformed in colorless products, and in effective contact with said color coupler a compound capable of forming an acid-resistant dye by oxidative coupling with said color coupler,

2. developing the photographic element in a color-forming developer,

3. treating the photographic element in an oxidative bleaching bath,

4. fixing the photographic element, and

5. treating it in a strong acidic solution the hydrogen concentration of which is at least 10 ^-1 gram equivalent per liter, the steps (4) and (5) being carried out in either order, to produce colorless reaction products at the places where development occurred, as well as a positive color image of the object to be reproduced formed by said oxidative coupling at the non-developed areas of the photographic element where color coupler was still present after the development.

A colored direct positive image can also be produced by means of a process using compounds that react with the oxidation product of a developing agent to form therewith colorless products in the exposed parts of a silver halide emulsion layer. These compounds possess preferably themselves no developing activity and do not react with the oxidation products of the developing agent(s) or only react therewith to form colorless substances.

These compounds react with the oxidation products of amidrazones, the vinylene homologues of the amidrazones, the phenylene homologues of the amidrazones or the azavinylene homologues of the amidrazones to form colored products.

The amidrazones are compounds containing the structural group :

Vinylene homologues, phenylene homologues and azavinylene homologues are those which contain a vinylene group, a phenylene group or an azomethine group in the above structural group between the carbon atom and thereto singly bonded nitrogen atom.

Said process for the production of direct-positive dye images more particularly includes the steps of :

a. image-wise exposing a photographic material, which contains at least one silver halide emulsion layer containing an effective amount of a compound capable of reacting with the oxidation products of photographic color developers to form colorless products,

b. developing with a photographic developing agent,

c. bleaching with an oxidizing bleaching bath, and

d. fixing,

the oxidizing bleaching being performed in effective contact with such compounds that are capable of reacting with developer oxidation products to form substances which are colorless at the end of the photographic processing and being performed in effective contact with amidrazones, vinylene homologues of the amidrazones and azavinylene homologues of the amidrazones allowing said compounds to react with the oxidation products of the amidrazones to form colored products.

The compounds that are used to react with the oxidation products of the amidrazones to form colored products are preferably selected from the group consisting of arylamines, compounds of the 5-amino-Δ-2-pyrazoline series and compounds of the 1-phenyl-Δ-2-pyrazolone series.

More particulars about said process and compounds used therein can be found in the U.K. Pat. specification No. 1,123,782 filed July 23, 1965 by Agfa A.G. and the U.S. Pat. spec. No. 3,443,942 issued May 13, 1969 by W.Puschel and K.W. Schranz.

The amidrazones mentioned therein are also suited for the formation of a positive dye image by oxidative copulation with color couplers of the phenol, α-naphthol and pyrazolone type that remained after color development in the non-exposed silver halide emulsion portions (see therefor e.g., the U.S. Pat. spec. No. 3,245,788 and 3,245,787).

Of course, for producing a reversal color image the conventional method can be applied, which comprises the consecutive steps of image-wise exposing a light-sensitive silver halide reversal material, developing the exposed silver halide in a black-and-white developing composition, rinsing, re-exposing the material uniformly to actinic light so as to form a latent image in the residual silver halide, developing said latent image in a color developing composition, and bleaching, rinsing and drying the material. The second exposure can be omitted if the material is treated in a solution of a fogging agent such as hydrazine or a semi-carbazide, e.g., 10 g of semicarbazide hydrochloride per liter. The fogging agent may be added directly to the second developer.

Particular photographic processing liquids for the treatment of the kind of material described are disclosed in our published Dutch Patent application No. 6713674 filed Oct. 8, 1967 by Gevaert-Agfa N.V. relating to photographic processing liquids and methods of producing photographic images.

Negative and positive color images can also be produced in the same recording material by means of a process based on the image-wise diffusion of compounds such as complexed silver salts.

For the purpose of the present invention the silver halide complex diffusion transfer is applied in order to obtain a negative and positive silver image in different layers of a same recording material. Therefore, a recording material contains a layer which comprises development nuclei applied in a layer onto or under the silver halide emulsion layer e.g., onto the support of a silver halide emulsion layer.

According to a proper embodiment the silver halide emulsion layer contains a bleachable dye, e.g., a blue azo dye, and in or onto the development nuclei-containing layer or sheet a bleachable yellow dye. After development of the silver image at the exposed areas and diffusion transfer and development of the complexed silver salts at the unexposed areas a positive blue image is obtained by silver dye bleach processing in the emulsion layer and a negative yellow image in or on the development nuclei-containing layer or sheet.

Positive and negative color images of contrasting colors can also be obtained according to an embodiment based on the diffusion transfer of colored developing agents, in the same recording material.

In such process a colored developing agent can be applied in a colloid layer beneath a silver halide emulsion or in the emulsion layer itself, which layer contains a dye e.g., a blue azo dye that can be bleached with the aid of silver. The colored developing agent, e.g., yellow developing agent, is of the hydroquinone type being alkali-soluble in non-oxidized state and may contain a chromophoric group that is less sensitive for bleaching in the presence of silver than the azo dye present in the emulsion layer. Suitable colored developing agents for that purpose are described in the Canadian Pat. specification No. 598,786 filed Apr. 1, 1959 by Polaroid and the U.S. Pat. No. 3,245,790 of J.F. Downey and N.S. Simon issued Apr. 12, 1966. During development the colored developing agent diffuses from the silver halide emulsion layer in the unexposed areas into an overlying colloid layer and is fixed therein. Thereupon a silver dye bleach processing is applied, whereby the bleachable azo dye and possibly also the oxidized alkali-insoluble developer dye are removed from the emulsion layer in correspondence with the silver image. In that way, e.g., a blue and a yellow image of opposite gradation are obtained in the same recording material.

According to another embodiment based on the principles of diffusion transfer image formation, a colored negative and positive image of opposite gradation can be produced in a receiving material by means of a recording material, which is built up, e.g., in the following way :

1. a transparent water-impermeable film support,

2. a colloid layer containing a yellow developing agent of the hydroquinone type,

3. a direct-positive emulsion layer,

4. an interlayer,

5. a colloid layer containing a blue developing agent of the hydroquinone type, and

6. a silver halide emulsion layer of the negative type.

After exposure and processing which includes the development of the emulsion layers by their respective colored developing agents the latter which are not fixed (i.e. which have not been made resistant to diffusion in the quinone form) are transferred by means of the alkaline processing solution from the non-silver image areas to a receptor layer or sheet, e.g. paper or film, coated with a colloid layer and optionally absorbed thereon with the aid of mordanting agent. Self-explanatory after bleaching the silver images in the recording material a bi-color image of opposite gradation will be left therein.

Referring again to the silver dye bleach process it is possible to use a combination of separate silver halide emulsions which yield a negative and a positive image respectively by a proper exposure and development. E.g., the said emulsions are applied to opposite sides of a light-transmitting film support, which during a direct exposure with penetrating rays may be opaque or coated with an opaque interlayer, which can be bleached or decolorized in one of the processing liquids. With such an arrangement it is possible to expose one of the emulsion layers only to the penetrating rays and the other emulsion layer to penetrating rays and to light, e.g., produced by means of the penetrating rays in a fluorescing screen.

An interlayer between the emulsion layers may also act as filter layer whereby one of the emulsion layers during an indirect exposure (e.g. from a fluorescing screen with phosphors emitting in the visible and/or U.V.spectrum) is exposed to light of a wavelength range, which differs from the light to which the other silver halide emulsion is exposed.

In the silver halide emulsions applied according to the present invention different types of silver halide can be used e.g., silver chloride, silver bromide, silver chlorobromide, silver chlorobromideiodide, silver chloroiodide or silver bromide iodide or mixtures thereof. Iodide-containing bromide emulsions, preferably containing up to 10 mole percent of iodide are especially useful for directly or indirectly recording penetrating radiation.

Particularly suited e.g., for exposure with the aid of fluorescent tungstate screens are silver bromide-iodide emulsions containing from 10 to 2 mole percent of iodide and corresponding with 5 to 16 g of silver nitrate per sq.m. A more preferred silver halide content corresponds with 6 to 12 g of silver nitrate per sq.m.

The colloid binder of the silver halide preferably essentially consists of gelatin, and preferably is present in an amount of 3 to 7 g per sq.m in a single silver halide emulsion layer.

When one of the color images is formed by color couplers incorporated in one of the silver halide emulsion layers an amount of silver halide is used preferably in excess of 50 to 150 percent in respect of the equivalent amount necessary in the dye forming reaction using exposed silver halide and a color developing agent of the P-phenylene diamine type.

Although the color couplers are preferably incorporated in the silver halide emulsion colloid in diffusion resistant state they may be applied also in dissolved state from the developing bath. The color couplers are made resistant to diffusion in hydrophilic colloid layers by techniques known in the art e.g., by the use of color coupler molecules with fairly long aliphatic carbon chains (e.g. C ₅ -C ₂₀ ) or incorporation of the color couplers in droplets of high boiling organic water-immiscible liquids so-called oil-formers.

The support of the silver halide emulsion layers suited for use according to the present invention is preferably a transparent resin support. Transparent resin supports for use in photographic silver halide materials are generally known. In common materials cellulose triacetate supports are used and where a high dimensional stability is required preferably a polyester resin support e.g., of polyethylene terephthalate is used.

Most preferred radiographic recording materials e.g., suited for use in an exposure with fluorescing screens contain at both sides of the support a silver halide emulsion layer incorporating the necessary substances for forming the desired images contrasting in color tone (hue) and being of opposite gradation.

As developing agents for forming azomethine or quinoneimine dyes preferably aromatic primary amino developing agents of the p-phenylene diamine type are used e.g., p-phenylene-diamine, N,N-diethyl-p-phenylenediamine, N-butyl-N-sulphobutyl-p-phenylenediamine, 2-amino-5-diethylaminotoluene hydrochloride and 4-amino-N-ethyl-N(β-methane-sulphonamido-ethyl)-m-toluidine sesquisulphate monohydrate or N-β-hydroxyethyl-N-ethyl-p-phenylene-diamine.

In rapid processing at higher temperatures (35°-45°C) preferably N-butyl-N-sulphobutyl-p-phenylenediamine and/or N-β-hydroxyethyl-N-ethyl-p-phenyleneadiamine are used.

The radiation-sensitive materials for use according to the present invention, in addition to the desired color coupler may contain all kinds of ingredients characteristic for silver halide materials used for direct or indirect recording of penetrating radiation.

So, the radiation-sensitive silver halide emulsions may contain sensitizing and/or screening dyes.

According to a special embodiment, selectively working desensitizing dyes are used which lower the sensitivity to visible light without substantially affecting the X-ray sensitivity. For such dyes reference is made to French Pat. specification No. 1,529,155 filed June 21, 1967 by Gevaert-Agfa N.V. corresponding with published Dutch Pat. application No. 67/08637 filed June 21, 1967 by Gevaert-Agfa N.V.

For the purpose of accelerating the development, the exposed silver halide is preferably developed in the presence of water-soluble alkylene oxide condensation products or polymers as described, e.g., in the U.S. Pat. No. 1,970,578 of C.Scholler and M.Wittwer, issued Aug. 21, 1934, U.S. Pat. No. 2,240,472 of D.R. Swan issued Apr. 29, 1941, U.S. Pat. No. 2,423,549 of Ferdinand Schulze, issued July 8, 1947, U.S. Pat. No. 2,441,389 of R.K. Blake, issued May 11, 1948, U.S. Pat. No. 2,531,832 of W.A. Stanton, issued Nov. 28, 1950, U.S. Pat. No. 2,533,990 of R.K.Blake, issued Dec. 12, 1950 and the U.K. Pat. specifications Nos. 991,608 filed June 14, 1961 by Kodak Ltd., 920,637 filed May 7, 1959, 945,340 filed Oct. 23, 1961, 940,051 filed Nov. 1, 1961 and 1,015,023 filed Dec. 24, 1962 all by Gevaert Photo-Producten N.V. For suitable development accelerating polymeric products of another type, reference is made to our published Dutch Patent applications No. 66/14230 filed Oct. 10, 1966 and 66/14291 filed Oct. 11, 1966. Other compounds that sensitize the photographic emulsion by development acceleration are organic onium compounds and polyonium compounds, preferably of the ammonium or sulphonium type, e.g., quaternary tetraalkylammonium salts, alkyl-pyridinium salts, bis-alkylene-pyridinium salts, alkyl-quinolinium salts, and trialkyl-sulphonium salts.

The silver halide can further be combined with chemical sensitizers known in the art such as sulphur-containing sensitizing compounds e.g., allyl isothiocyanate, allylthiourea, reducing compounds such as the tin compounds described in the Belgian Patent specifications Nos. 493,464 filed Jan. 24, 1950 and 568,687 filed June 18, 1958 both by Gevaert Photo-Producten N.V., or noble metal compounds such as gold, platinum, palladium, iridium, ruthenium and rhodium compounds.

The silver halide emulsions used according to the present invention can also contain known stabilizing agents for silver halide emulsions, e.g., mercury compounds, sulphur compounds such as 1-phenyl-2-tetrazoline-5-thione, the compounds described in the Belgian Pat. specifications Nos. 571,916 and 571,917 both filed Oct. 10, 1958 by Gevaert Photo-Producten N.V., either or not in combination with chemically sensitizing and stabilizing cadmium salts in the light-sensitive material as well as in the developer.

Together with the above-mentioned ingredients, derivatives of tetra-azaindenes, e.g., having the following general formula, may be used as fog-inhibiting compounds in the light-sensitive material : ##SPC5##

wherein :

each of R ₁ and R ₂ represents a hydrogen atom, an alkyl, an aralkyl, or an aryl group, and

R ₃ represents a hydrogen atom, an alkyl, a carboxy, or an alkoxy-carbonyl group.

The processing of the radiation-sensitive film used for producing color radiographs according to the present invention may occur in conventional deep-tank processors including a drier, e.g., the Gevamatic S (trade name) automatic processor for industrial X-ray films, the wet-treatment stations being provided with the appropriate liquid compositions, or in apparatus wherein the application of one or several processing liquids to the film occurs by a lick-roller, a kiss-roller, or any other system capable of applying to one side of the film only a limited and premetered quantum of processing composition. The processing may also be carried out manually by the operator, who attaches the film to the clips of a frame which is successively dipped into the different processing tanks.

If a reversal image is to be produced at only one side of the film by uniform re-exposure, the re-exposure device may be arranged to illuminate the film at one side. The penetration of light into emulsion layers at the other side of the film may be prevented by dyed intermediate layers absorbing said radiation. During or after the completion of the processing the dye of said layers may be bleached or otherwise eliminated.

The following examples illustrate the present invention, without limiting, however, the scope thereof in any way.

EXAMPLE 1

Four g of a yellow azo-dye corresponding to the following structural formula: ##SPC6##

prepared as described in the published Dutch Patent application No. 6510695 filed Aug. 16, 1965 by Gevaert-Agfa N.V. (dye XVII) were dissolved in 400 ml of a 4 percent aqueous gelatin solution and added in the dark to 800 ml of a molten silver bromide emulsion. This emulsion portion contained 15 g of silver in the form of silver bromide and was stabilized by means of 4-hydroxy-6-methyl-1,3,3a,7-tetra-azaindene.

As illustrated in FIG. 2 the emulsion was coated onto a cellulose triacetate support 13 in such a way that it formed onto a subbing layer 14 a yellow colored emulsion layer 17 containing per sq.m 0.6 to 9.0 g of silver in the form of silver bromide.

At the other side of the support a silver bromide-iodide (2 mole percent of iodide) emulsion was coated onto a subbing layer in such a way that an emulsion layer 17 was formed containing per sq.m an amount of silver halide corresponding with 9 g of silver nitrate and an amount of 1.5 g of a colorless cyan-forming coupler according to the following formula : ##SPC7##

melting point : 108°C.

(prepared according to preparation 1 of U.K. Pat. specification No. 1,104,729 filed Oct. 13, 1965 by Gevaert-Agfa N.V.).

The emulsion layers were covered with antistress layers 18.

The recording material 12 was image-wise exposed as illustrated in FIG. 3 by means of an X-ray radiation source 10, the radiation source 10, the radiation of which was image-wise transmitted through the original 11 representing a cast metal part of a machine. The film was developed with a p-phenylenediamine type developing agent. On both sides of the support a silver image was formed. A cyan image was only formed in the emulsion layer 15 containing the cyan-forming color coupler. Thereupon both emulsion layers were fixed and rinsed.

The azo-dye was image-wise destroyed and the silver was bleached in the emulsion layer 17 by means of a liquid having the following composition :

potassium iodide 10 g sodium hypophosphite 10 g sulphuric acid 66° Be 50 ml quinoline 50 ml 2,3-dimethylquinoxaline 20 mg water 1,000 ccs

The bleaching liquid was applied by means of a spraying device only moistening the film side carrying the azo-dye. After a working contact of 25 min. the film was rinsed and the residual silver was completely bleached by means of a solution consisting of :

copper (II) chloride 25 g strong aqueous hydrochloric acid 5ccs water 1000 ccs

The silver image at the film side carrying the cyan image was bleached in an alkaline bleaching bath comprising potassium hexacyanoferrate (III). Finally both emulsions were treated with a fixing solution and rinsed.

The composition of the radiographic color image obtained is shown in Fig. 4.

The layer 15 contained a negative cyan image of the original which image is indicated in the layer 15 by the shaded portion. The layer 17 contained a positive yellow image of the original 11. The shaded portions of said layer are yellow because in these areas the yellow azo-dye remained unaffected.

The light box on which the radiograph was examined was provided with a light yellow filter in the form of a cellulose triacetate support provided with a yellow gelatin layer. On inspection with yellow light the contrast of the cyan parts of the image, and particularly those of low densities, say from 0.05 to 0.03, corresponding e.g., with fissures and other defects in the radiographed metal part, was increased whereas that of the yellow parts of the image was reduced.

EXAMPLE 2

To 500 ml of a silver bromide-iodide emulsion were added 300 ml of a 3 percent aqueous gelatin solution containing 2 g of a cyan azo-dyestuff having the following structural formula: ##SPC8##

prepared according to the general preparation method for compound 7 of the published Dutch Pat. application No. 6603572 filed Mar. 18, 1966 by Gevaert-Agfa N.V.

The emulsion was coated as illustrated in FIG. 5 in such a way onto a polyethylene terephthalate support 20 carrying subbing layers 21 and 22 that it contained in the dried layer 25 an amount of silver halide corresponding with 0.8 g of silver per sq.m.

At the other side of the support silver bromide-iodide emulsion (3 mole percent iodide) layers 23 and 24 were coated. Both emulsion layers were of the negative type. The emulsion layers 23 and 24 contained an amount of silver halide corresponding with 8 g of silver nitrate per sq.m. Emulsion layer 23 contained in addition per sq.m.

1.5 g of a colorless magenta-forming color coupler of the formula: ##SPC9##

Melting point : 250°C (decomposition), prepared as described in the U.S. Pat. specification No. 3,330,660 of Raphael Karel Van Poucke, Arthur Henri De Cat and Marcel Jacob Monbaliu issued July 11, 1967 (preparation 1).

The emulsion layer 24 contained a yellow-forming color coupler having the following formula : ##SPC10##

Melting point : <250°C, prepared as described in Belgian Pat. specification No. 725,904 filed Dec. 23, 1968 by Gevaert-Agfa N.V. (preparation 3).

The described radiographic film was image-wise exposed to the object 11 of FIG. 3 and thereupon processed as described in Example 1.

The radiographic image obtained was composed as illustrated in FIG. 6. The layer 23 contained a negative magenta image of the object 11 of FIG. 3, as indicated by the shaded portion. The layer 24 contained a negative yellow image of the object 11, indicated by the shaded portion.

The optical result of both superimposed images was a red negative image of the original.

The layer 25 contained a positive cyan image of the original. At the non-shaded portion the cyan dye has been destroyed in proportion to the amount of silver present.

It is evident that the composition of the film material described may be changed without changing the color rendering of the image. E.g., the layers 23 and 24 may be replaced by one layer containing yellow forming as well as magenta-forming color couplers.

EXAMPLE 3

In FIG. 7 a cellulose triacetate support 30 having subbing layers 31 and 32, was coated at one side of the support with a silver bromide emulsion layer 33 of the negative type containing a bleachable cyan azo-dye, as described in Example 2 and at the other side of the support with a silver halide emulsion layer 34 of the direct positive type as described in the published U.K. Pat. specification No. 1,155,404 filed May 9, 1966 by Gevaert-Agfa N.V. (see Example Test Series A) containing a spectrally sensitizing dye : ##SPC11##

methine dye : ##SPC12##

and containing a bleachable yellow azo-dye as described in Example 1, and antistress layers 35 and 36.

The radiographic film was image-wise exposed to the original 11 as illustrated in FIG. 3 and black-and-white developed in order to obtain a negative and positive silver image in the yellow and cyan emulsion layers respectively. The bleaching of the azo-dyes was carried out as described in Example 1 and a positive cyan and negative yellow image of opposite gradation were obtained in the same recording material as represented by the shaded areas in the layers 33 and 34 of FIG. 8.

EXAMPLE 4

One-hundred g of a silver bromide-iodide (9 mole percent of iodide) emulsion were diluted with 100 ccs of water, 13 ccs of 0.5 N aqueous succinic acid and 10 ccs of 1 percent aqueous saponine solution.

To this emulsion were added 1.8 g of a colorless oxidatively coupling compound A of the formula : ##SPC13##

1.2 g of blue-forming color coupler B of the formula : ##SPC14##

in 20 ccs of isopropanol and 10 ccs of 0.5 N aqueous sodium hydroxide. The emulsion was coated in such a way that it contained an amount of silver halide corresponding with 9 g of silver nitrate per sq.m. After the addition of the necessary hardening and wetting agents the photographic emulsion was applied to a cellulose triacetate film support. The obtained light-sensitive emulsion layer was exposed through a grey wedge with fluorescing light produced by means of penetrating X-rays in a fluorescing calcium tungstate screen.

The light-sensitive material was developed in a developing liquid having the following composition :

N,N-diethyl-p-phenylenediamine 3 g sulphate sodium sulphite 4 g sodium carbonate 50 g potassium bromide 1 g hydroxylamine-hydrochloride 1.5 g water 1000 ccs

A blue negative wedge print was obtained. The absorption maximum of the dye was at 625 mμ.

After rinsing for 4 min., the developed silver image was bleached for 3 min. in an alkaline bleaching bath having the following composition :

sodium hydrogen sulphate 4 g borax 20 g potassium bromide 15 g potassium hexacyanoferrate (III) 100 g water 1000 ccs.

During bleaching an orange print (absorption maximum : 476 nm) of the wedge was obtained having an opposite gradation in respect of the blue wedge print (see FIG. 1).

After 3 min. of rinsing the bleached recording material was fixed in a fixing bath of the following composition :

ammonium thiosulphate 100 g sodium sulphite 15 g sodium metabisulphite 5 g water till 1000 ccs

and rinsed for 10 min.

PREPARATION OF THE BLUE FORMING PHENOL COUPLER B

a. One hundred and fifty-four g (1 mole) of 5-nitro-2-aminophenol were dissolved in 1.5 1 of water-free acetone. Under stirring 100 g (1.2 mole) of anhydrous sodium hydrogen carbonate were added. At 20°C 109 ml (1 mole) of 2-furoyl chloride were dropwise added. The temperature rose from 20 to 30°C and the final product started to precipitate. The obtained mixture was stirred for about 4 hours until all the 5-nitro-2-aminophenol was transformed. The precipitate formed was filtered with suction and washed with acetone, until the filtrate was colorless. In order to eliminate any sodium hydrogen carbonate still present, the precipitate was stirred for about 40 min. in 1.5 liter of hot water, filtered with suction and washed with water. The purified precipitate was dried in a cold ventilated drying oven. Yield : 220 g (89 percent). Melting point : beyond 260°C.

b. Three hundred and twenty-seven g (1.5 mole) of 2-(2'-furoylamino)-5-nitro-phenol prepared as described under a) together with 25 ml of Raney nickel in 3 liter of dimethylformamide were reduced at 60-65°C under 1,500 psi of hydrogen pressure. The reaction lasted about 3 hours. After filtering off the Raney nickel, the filtrate was concentrated by evaporation on the water jetpump, and allowed to solidify with stirring under water. The precipitate obtained was filtered with suction, washed with water and dried. Yield : 262 g (91 percent). Melting point : 184°-186°C.

c. Two hundred and eighteen g (1 mole) of 2-(2'-furoylamino)-5-amino-phenol prepared as described under (b) and 386 g (1.2 mole) of hexadecenylsuccinic anhydride were refluxed for 30 min. in 3 liter of acetonitrile. In order to avoid crystallization from the reaction mixture, 60 ml of acetic acid were added to the acetonitrile. After cooling, the precipitate formed was filtered with suction, dried and recrystallized from di-chloroethane. Yield : 442 g (82 percent). Melting point : 134°C.

PREPARATION OF THE OXIDATIVELY COUPLING COMPOUND A.

Eight hundred and fifteen g (3 mole) of 1-nitro-2-chloro-5-difluoromethylsulphonylbenzene were suspended at 80°C in 1 liter of water. A second solution was prepared by dissolving 2,160 g of sodium sulphide-9-water (9 mole) in 1,500 ml of warm water, whereupon 306 g (9 mole) of hydrogen sulphide were introduced. The latter solution was dropwise added to the first one with stirring at 80°-100°C. Then the mixture was stirred for further 30 min. and cooled to 35°C. At this temperature 362 ml (6 mole) of carbon disulphide were added dropwise. The mixture was heated for 1 hour at 60°-65°C, and thereafter for 4 hours at 90°-95°C. It was allowed to cool whereupon the precipitate formed was filtered with suction. In closed apparatus the precipitate was dissolved in warm water and acidified with concentrated hydrochloric acid (evolving hydrogen sulphide is collected in sodium hypochlorite solution).

The precipitate was filtered with suction and dissolved in 0.5 N ammonium hydroxide. After filtration it was acidified with hydrochloric acid. The precipitate formed was filtered with suction and washed with water until neutral. Yield : 526 g (62 percent) of 5-difluoromethylsulphonyl - benzothiazole-2-thione. Melting point : 243°-244°C.

Five hundred and sixty-two g of the latter product were dissolved in alcoholic potassium hydroxide with stirring, prepared by dissolving 134 g of potassium hydroxide in 3 liter of ethanol. At 60°C 208 ml (2.4 mole) of dimethyl sulphate were added dropwise, whereupon the mixture was stirred 1 further hour at this temperature. This mixture was poured in 30 liter of water. The precipitate formed was filtered with suction, dried and recrystallized from about 5 liter of ethanol. Yield : 490 g (83 percent) of 2-methylmercapto-5-difluoromethylsulphonyl-benzothiazole. Melting point : 127°C.

147.5 g (0.5 mole) of the latter product and 372 g (2 mole) of methyl p-tolusulphonate were molten for 2 days at 120°C was stirred. After cooling, the reaction mixture was finely rubbed under ether. The precipitate was filtered with suction, washed first with a little or dry acetone and then with ether. The precipitate was dried for about 2 hours (it decomposed at the air). Yield : 228 g (95 percent) of 2-methylmercapto-3-methyl-5-difluoro-methylsulphonyl-benzoth iazolium p-tolusulphonate. Melting point : 210°C (unsharp).

Three hundred and ninety-five g (0.75 mole) of 1-chlorocarbonyl-2-n-hexadecylsulphonyl-5-chlorosulphonylben zene were refluxed in 750 ml of dioxan. After the addition of 58 ml of distilled water, the reaction mixture was heated some further 8 min. This mixture was poured into a cooled flask and cooled quickly. The precipitate formed was filtered with suction, washed with acetonitrile, and dried as quickly and as thoroughly as possible). Finally the precipitate was recrystallized from about 3 liter of naphtha. Yield : 318 g (84 percent) of 2-hexadecylsulphonyl-5-chlorosulphonyl-benzoic acid. Melting point : 104°-105°C.

Two hundred and fifty-four g of the latter product (0.5 mole) were dissolved in 3 liter of dioxan (at 30°-35°C if necessary) and added dropwise to a stirred and cooled solution of 750 ml of hydrazine hydrate in 1 liter of dioxan in such a way, that the temperature was maintained below 13°C. This mixture was stirred for 1 further hour at about 15°C. The mixture was then acidified below 15°C with concentrated hydrochloric acid. Thereupon about 6 liter of water were added slowly. The precipitate formed was filtered with suction, washed with water until neutral and dried. Yield : 252 g (100 percent) of 2-hexadecylsulphonyl-5-hydrazinosulphonyl-benzoic acid. Melting point : 160°C (unsharp).

One hundred and ninety-two g of 2-methylmercapto-3-methyl-5-difluoromethylsulphonylbenzimida zolium p-tolusulphonate (0.4 mole) and 252 g (0.5 mole) of 2-hexadecylsulphonyl-5-hydrazinosulphonyl-benzoic acid were heated at 40°C in 1,250 ml of pyridine for 3 days. The reaction mixture was evaporated until a third part of its original volume at 40°C under reduced pressure. During all these treatments the evolving methylmercaptane was collected in a washing bottle and destroyed with sodium hypochlorite solution. The concentrated reaction mixture was then poured on about 6 kg of ice mixed with 750 ml of concentrated hydrochloric acid. As soon as the precipitate was solid, it was filtered with suction, washed with water and dried. First it was recrystallized from about 4.5 liter of ethanol and then from about 1.7 liter of dichloroethane.

Yield : 205 g (67 percent) of the compound according to the formula : ##SPC15##

Melting point : 208°C.

EXAMPLE 5

A polyester resin support provided at both sides with subbing layers for gelatin coatings was coated on both sides with a silver bromide-iodide emulsion (3mole percent of iodide). Each dried emulsion layer contained per sq.m an amount of silver halide corresponding with 9 g of silver nitrate, 4.5 g of a red colored color coupler having the following structural formula : ##SPC16##

and forming a cyan dye on copulation with an oxidized p-phenylenediamine type developing agent, and 4 g of a colorless cyan-forming color coupler having the following structural formula : ##SPC17##

(prepared according to Fiat Final Report 943 p. 68).

After a direct exposure with an X-ray tube (tungsten anti-cathode) working at 60 kV/150 mA.s at a distance of 100 cm of the radiographic material, which was placed in a film cassette incorporating two calcium tungstate screens (intensifying coefficient 2), the material was developed at 20°C in the following developing composition :

benzyl alcohol 5 ml anhydrous sodium sulphite 5 g sodium hydroxide (pellets) 5 g trisodium phosphate-12-water 25 g 4-amino-N-ethyl-N-(β-methanosul- phamido ethyl)-m-toluidine 10 g ethylenediamine tetraacetic acid trisodium salt 8 g potassium bromide 1 g water to 1 liter

After development the material was treated in a stop-bath having the following composition :

glacial acetic acid 10 ml sodium acetate-3-water 10 g water to 1 liter

Thereupon the material was treated for the removal of the silver image in a bleaching bath having the following composition :

potassium hexacyanoferrate(III) 50 g potassium thiocyanate 7.5 g potassium bromide 15 g disodium phosphate-12-water 1.5 g water to 1 liter

Then the material was fixed in a fixing bath having the following composition :

sodium thiosulphate-5-water 150 g sodium hydrogen sulphite 15 g water to 1 liter

Finally the material was rinsed and treated in a hardening or stabilizing bath containing 25 ml of a 40 percent aqueous solution of formaldehyde.

A negative cyan image together with a positive red image was obtained in both the emulsion layers.

PREPARATION OF THE RED COLOR COUPLER

7.6 g of 4-acetamino-2-aminobenzene sulphonic acid were dissolved in 50 ml of 1N sodium hydroxide. To this solution were added 2.3 g of sodium nitrate, whereupon this solution was added at 0°-5°C to a mixture consisting of 50 ml of concentrated hydrochloric acid and 25 ml of water. In this way a suspension of the corresponding diazonium salt was obtained.

This diazonium salt solution was dropwise added to a solution of 18.5 g of 1-hydroxy-2'(N-methyl-N-n-octadecylamino)-5'-sulpho-2-naphth anilide in 300 ml of methanol, while an amount of sodium hydroxide solution was added necessary to keep the pH at 8-9. Thereupon the mixture was stirred for another 2 hours, whereafter the dye precipitated was filtered with suction, washed with methanol and dried under reduced pressure. The red dye obtained possessed an absorption maximum at 462 nm in gelatin.

EXAMPLE 6

Example 4 was repeated but instead of the therein described blue-forming color coupler the recording material contained the blue-forming color coupler having the following structure : ##SPC18##

Melting point : 174°C.

A blue negative image having an absorption maximum at 615 nm and a yellow positive image (absorption maximum at 436 nm) were obtained.

PREPARATION OF THE BLUE-FORMING COLOR COUPLER

a. 15.4 g of 2-amino-5-nitro-phenol were dissolved in 100 ml of dry acetone and 13.8 g of palmitoyl chloride were added thereto. The obtained mixture was stirred for 1 hour and thereupon poured in 1 liter of water. The precipitate formed was filtered by suction and washed with boiling water. After drying the crude 2-palmitoylamino-5-nitro-phenol was recrystallized from methanol. Melting point : 150°C.

b. One hundred and eighty g of 2-palmitoylamino-5-nitro-phenol were hydrogenated in a shaking autoclave containing 240 ml of dimethylformamide and 2 g of Raney nickel. The hydrogenation producing 2-palmitoylamino-5-aminophenol was carried out at 50°C and lasted 4 hours. The hydrogenation mixture was concentrated by partly evaporating the dimethylformamide and the concentrate poured into water. The precipitate formed was filtered with suction and washed with water. After drying the crude 2-palmitoylamino-5-amino-phenol was recrystallized from acetonitrile. Melting point : 120°C.

c. 36.2 g of 2-palmitoylamino-5-amino-phenol were dissolved in 300 ml of acetonitrile and 15 g of phthalic anhydride added thereto. The precipitate formed by cooling was filtered with suction and the obtained color coupler recrystallized from acetic acid. Melting point : 174°C.

EXAMPLE 7

Example 4 was repeated but the cited blue-forming color coupler in the recording material was replaced by the blue-forming color coupler P having the formula : ##SPC19##

melting point : 156°C. (Prepared analogously to the color coupler of Example 4).

As compound for the copulation in the bleaching bath with this color coupler an oxidatively coupling compound Q was used corresponding to the formula : ##SPC20##

melting point : >260°C.

A blue negative image (absorption maximum : 610 nm) and a red positive image (absorption maximum : 523 nm) were obtained in the emulsion layer.

PREPARATION OF THE OXIDATIVELY COUPLING COMPOUND Q

a. In a 3 liter three-necked flask fitted with a thermometer, a mechanical stirrer and a dropping funnel scaled with a sodium hydroxide tube were dispersed 275.5 g of 3-nitro-4-chloro-benzene sulphonic acid potassium salt in 200 ml of water. The dispersion was heated till 80°C and a sulfide solution obtained by dissolving 960 g of Na ₂ S.9 water and 136 g of hydrogen sulphide in 500 ml of water, was added dropwise thereto. The reaction was exotherm and the temperature kept between 80 and 85°C. After the addition of the sulphide and reaction mixture was cooled till 40°C and while stirring 80 ml of carbon disulphide added dropwise thereto. In 1 hour the temperature was raised till 60°-65°C and kept for 5 hours at 90°-95°C. The reaction mixture was then cooled and filtered. Five-hundred-fifty ml of acetic acid were added dropwise and thereafter 500 ml of water. The precipitate formed was filtered with suction. The obtained 2-mercapto-4-sulphonic acid-benzthiazole-potassium salt had a melting point >260°C.

b. Two hundred and eighty-five g of 2-mercapto-4-sulphonic acid benzthiazole potassium salt were dissolved in a solution of 82 g of potassium hydroxide in 565 ml of water. The mixture was heated till 60°C and whilst stirring for 1 hour 99 ml of dimethyl sulphate added thereto. The reaction mixture was acidified with 200 ml of concentrated hydrochloric acid. The reaction mass was cooled till approximately 5°C and stirring continued for 2 hours. The precipitate was filtered with suction and washed with ethanol. Recrystallization was carried out with a minimum of water and the product acidified with 250 ml of concentrated hydrochloric acid. The obtained 2-methylmercapto-4-sulphonic acid benzthiazole had a melting point >260°C.

c. One hundred and forty g of 2-methylmercapto-4-sulphonic acid benzthiazole was allowed to react for 36 hours at a temperature of 135°C with 100 ml of dimethylsulphate. The obtained product was rubbed under dry acetone and two times washed with ether. The 2-methylmercapto-3-methyl-4-sulphonic acid-benzthiazolium tolusulphonate and 7.8 g of 3-sulphonylhydrazino-6-sulphonyl n-hexadecyl benzoic acid were allowed to react for 3 days at 70°C in a mixture of 80 ml of pyridine and 20 ml of piperidine. The obtained solution was concentrated under diminished pressure and the obtained solid treated with methanol. The solution was filtered and acidified with ethanolic hydrochloric acid. The obtained crystals were filtered with suction and washed with methanol. Melting point of the obtained oxidative coupling compound above 260°C.

EXAMPLE 8

A first silver halide emulsion layer was coated onto one side of a cellulose triacetate base. The said emulsion layer contained per sq.m 0.01 mole of silver halide consisting of 0.5 mole percent of iodide, 72.5 mole percent of bromide and 27 mole percent of chloride as well as 1.35 g of magenta-forming color coupler A having the formula : ##SPC21##

melting point : 239°C (prepared analogously to the couplers described in the United States Patent No. 2,673,801 of Joseph Jennen issued Mar. 30, 1954).

To the other side of the cellulose triacetate base a second silver halide emulsion layer was applied. It contained per sq.m 0.09 mole of silver halide consisting of 2 mole percent of iodide and 98 mole percent of bromide as well as 0.8 g of cyan-forming color coupler B having the formula : ##SPC22##

melting point : 181°C (prepared analogously to the coupler of Fiat Final Report 943 p. 67-69) and 0.7 g of a compound C that oxidatively couples in the bleaching bath with the latter color coupler B and has the following formula : ##SPC23##

From an alkaline solution in ethanol these compounds were added in dissolved state to the emulsions, and the pH of the latter was adjusted to 7 by means of acetic acid.

Both emulsion layers were provided with a common gelatin antistress layer.

After a direct exposure to a skull phantom by means of penetrating X-ray radiation the exposed recording material was developed for 8 min. in a developing bath having the following composition :

sodium hexametaphosphate 2 g anhydrous sodium sulphite 4 g N,N-diethyl-p-phenylenediamine 3 g hydrochloride hydroxylamine hydrochloride 1.5 g anhydrous sodium carbonate 57 g water till 1000 ml (pH=10.7)

the developed material was treated for 8 min. in the following intermediate alkaline bath :

sodium carbonate 30 g sodium hydrogen carbonate 10 g (pH=10.1)

the silver image was bleached for 4 min. in the following bath wherein bleaching and oxidative copulation to form an acid-resistant cyan dye with residual cyan-forming color coupler and the compound that oxidatively couples on the non-exposed portions took place simultaneously :

potassium hexacyanoferrate(III) 25 g potassium bromide 25 g sodium hexametaborate 20 g magnesium sulphate 50 g water till 1000 ml (pH=8.6)

the bleached material was rinsed for 4 min. in running water. The primary cyan image was destroyed by treating it for 8 min. in the following acidic bath :

strong sulphuric acid 25 ml potassium dichromate 5 g water till pH 0.2

the thus treated material was fixed for 4 min. in the following fixing bath :

ammonium thiosulphate 70 g sodium sulphite 96 g sodium hydrogen sulphite 4 g

After 8 min. rinsing the recording material was dried.

As final result in the exposed portions an acid-resistant magenta dye image was obtained in the first emulsion layer, and an acid-resistant cyan image in the non-exposed portions of the other emulsion layer.

PREPARATION OF THE OXIDATIVELY COUPLING COMPOUND C.

a. 35.5 g of 2-chlorobenzoylacetic acid ethyl ester and 14.5 ml of aniline were allowed to react in 150 ml of ethanol acidified with 0.3 ml of concentrated hydrochloric acid in the presence of 19 g of anhydrous magnesium sulphate. The reaction mixture was refluxed for 24 hours and filtered whilst still hot. Thereupon it was cooled down in a mixture of ice and water and the formed precipitate filtered with suction. The obtained ##SPC24##

melted at 96°C. b. 4.65 g of 2-chloro-β-anilinocinnamic acid ethyl ester were whilst stirring quickly added at 250°C to 50 ml of diphenyl ether. During the ring closure ethanol was distilled off. Stirring was continued for 10 min. at 250°C after the distilling off of the ethanol and the reaction mass cooled down. By adding ether a precipitate was formed which was filtered by suction and washed with ether. Recrystallization from a mixture of ethanol and water yielded ##SPC25##

melting point : 206°C.

c. 2.55 g of 2-ortho-chlorophenyl-quinoline-4-one were added to 5.5 ml of phosphorus oxytrichloride and allowed to react therewith for 2 hours at 80°C. Thereupon the reaction mixture was poured onto ice and the precipitate filtered with suction washed with water and dried. The obtained ##SPC26##

melted at 145°C.

d. 5.48 g of 2-ortho-chlorophenyl-4-chloroquinoline were allowed to react for 24 hours at 90°C in the absence of water with 10 ml of dimethylsulphate. The reaction mixture was cooled and dry ether added thereto. ##SPC27##

separated as an oily product.

e. 8 g of 2-ortho-chlorophenyl-4-chloroquinolinium methylsulphate were allowed to react with 9.12 g of 2-n-hexadecyloxy- 5-sulphonylhydrazino benzoic acid in 100 ml of anhydrous ethanol. The reaction lasted 1 hour and was carried out at reflux temperature. The reaction mixture was allowed to cool and neutralized with pyridine. Water was added and an oily residu formed separated. The oily residu was solidified by a treatment with acetonitrile and the solid filtered with suction. The precipitate was crystallized twice from acetonitrile. The obtained ##SPC28##

had a melting point of 110°C.

EXAMPLE 9

A cellulose triacetate support having subbing layers for gelatino silver halide emulsion layers at both sides was coated onto one side with a non-spectrally sensitized silver bromide-iodide emulsion (1.5 mole percent of iodide) containing per kg an amount of silver halide equivalent to 115.5 silver and 15 g of a colorless color coupler for cyan having the following structural formula : ##SPC29##

(for the preparation of the said coupler we refer to the United Kingdom Pat. specification No. 1,099,418 filed June 28, 1965 by Gevaert-Agfa N.V.). Melting point : 76°C.

The emulsion was coated at a rate of 1.5 g of color coupler per sq.m.

Onto the other side of the support a gelatino silver bromide emulsion was coated that mainly forms an internal latent image and little external latent image. The said emulsion was prepared by conversion of a silver chlorobromide emulsion (10 mole percent of bromide) by very slowly adding to said emulsion whilst stirring a 35 percent aqueous potassium bromide solution in an amount that is 90 percent higher than the stoichiometric amount. The emulsion was then kept for 1 hour at 60°C.

After the emulsion had been chilled and allowed to gel for 6 hours the emulsion was noodled. The noodles were washed for 1 hour with water (10 liters of water per minute). By heating the washed noodles a liquid silver halide emulsion was obtained containing 50 g of gelatin and an amount of silver bromide corresponding with 43 g of silver per kg.

To this liquid emulsion per kg 15 g of a color coupler for magenta corresponding to the following structural formula : ##SPC30##

and 20 mg of a spectrally sensitizing agent for the green region of the visible spectrum which corresponds to the following structural formula : ##SPC31##

Thereupon 20 ml per kg of a 5 percent solution in ethanol of 1-(o-methoxyphenyl)-2-tetrazoline-5-thione as antifogging agent were added.

Practically immediately thereafter the light-sensitive emulsion was coated on the cellulose triacetate support in such a way that an amount of silver halide equivalent to 5 g of silver nitrate was present per sq.m of light-sensitive material.

The emulsion layer was over-coated with a conventional hardened gelatin antistress layer.

The silver halide material obtained was exposed through an aluminum step-wedge by means of X-rays produced with a tungsten anti-cathode X-ray tube operating at 80 kV with a current of 100 mA. Thus, the material was developed for 3 min. at 26°C in a developer of the following composition:

N-ethyl-N-hydroxyethyl-p-phenylene diamine hydrochloride 10 g anhydrous sodium sulphite 4 g anhydrous sodium carbonate 50 g hydroxylamine hydrochloride 3 g water up to 1000 ccs

The development occurred for the first 30 seconds in the dark and then for the remaining time in green light obtained with a filter transmitting green light and a 15 Watt lamp placed at a distance of 70 cm from the light-sensitive material. Since the non-spectrally sensitized emulsion layer containing the color coupler for cyan was not sensitive for green light no over-all fogging could occur therein by the overall green light exposure necessary for developing the direct positive magenta image in the emulsion layer sensitive for green.

After the development the material was treated in a stop bath, bleached, fixed and rinsed with water as is conventional in the processing of photographic color materials.

A cyan negative wedge image was obtained in the non-spectrally sensitized emulsion layer and a magenta positive wedge image in the emulsion layer sensitive for green light. Compared with a direct positive image obtained in the same manner but with a light-sensitive emulsion layer containing no or at most one tenth of the stated amount of fog-inhibiting compound, the direct positive image prepared according to the present example showed a much lower minimum density and more clear image background.

According to a special method for improving the discernability of information in a radiograph, a photographic silver halide material is used containing at least two silver halide emulsion layers by means of which in one silver halide emulsion layer an image with a sensitometric curve having progressively increasing density values and in another silver halide emulsion layer an image with degressively increasing density values and of contrasting color with the first mentioned image can be obtained.

The sensitometric curves with opposite curvature of such images are illustrated in FIG. 9.

As a modification of said embodiment illustrated in FIG. 9 one of the silver halide emulsion layers yields an image with a sensitometric curve that has a normal rather large straight line portion, whereas another silver halide emulsion layer yields an image corresponding with a sensitometric curve with progressively or degressively increasing density values.

According to a preferred embodiment, the inertia values of the sensitometric curves of the radiograph of a sensitometric wedge used as an original are different, preferably in such a degree that the log E value of the shoulder of one curve corresponds with the log E value of the toe of the other curve.