GB2277166A - Colour correction - Google Patents

Abstract

Colours obtained in photographs are never a perfect reproduction of the colours in an original scene as a result of unwanted colour absorption in one or more of the dye layers which affects the overall performance of the imaging system. A method of correcting for unwanted colour absorption in at least one developed image dye layer of a colour negative film, e.g. green adsorption in cyan layer 38 comprises re-exposing the developed film with light having spectral characteristics similar to that of the unwanted colour absorption e.g. green such that the layer sensitive to this light e.g. magenta layer 36 is masked by the silver image 38b formed in the cyan layer 38 to form magenta images 36a' and silver images 36b' and further developing to form a masked image of the scene. <IMAGE>

Description

COLOUR CORRECTION Field of the Invention The present invention relates to colour correction and is more particularly, although not exclusively, concerned with colour correction in photographic imaging systems in which an image is captured on colour negative film and is then printed on colour paper.

Background of the Invention Photographic elements can be single colour elements or multi-colour elements. Multi-colour elements contain dye image-forming units sensitive to each of the three primary regions of the spectrum.

Each unit can be comprised of a single emulsion layer or of multiple emulsion layers sensitive to a given region of the spectrum. The layers of the element, including the layers of the image-forming units, can be arranged in various orders as known in the art.

In a alternative format, the emulsions sensitive to each of the three primary regions of the spectrum can be disposed as a single segmented layer.

A typical multi-colour photographic element comprises a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one greensensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, at least one of the couplers in the element being a coupler of this invention.

The element can contain additional layers, such as filter layers, interlayers, overcoat layers, subbing layers, and the like.

Colours obtained in photographs are never a perfect reproduction of the colours in an original scene as a result of various imperfections in the photographic imaging system. In particular, problems are caused by the fact that the simplest photographic systems attempt to reproduce the whole of the visible spectrum with just three dyes.

The most common photographic systems are based on the so-called subtractive dye system and use yellow, magenta and cyan imaging dyes to form the image. These imaging dyes often absorb light in spectral regions other than the desired regions. For example, cyan imaging dyes are used to absorb red light but often absorb some green light as well. This green light absorption is an unwanted absorption because it degrades the final colour reproduction performance of the overall photographic system.

Various methods are known for improving the colour reproduction of photographic images. Two commonly used ways to specifically overcome the problem with unwanted absorptions are to add coloured masking couplers or DI(A)R (development inhibitor (anchimeric) releasing) couplers to colour negative films.

Masking couplers may be those as described in EP-A-0 213 490; Japanese Application 58-172647; US-A-2 983 608; German Application DE-C-2 706 117; GB-A-1 530 272; Japanese Application A-113935; US-A-4 070 191 and German Application DE-A-2 643 965.

The masking couplers may be shifted or blocked.

DIR couplers are known in the art and examples are described in US-A-3 137 578; US-A-3 148 022; US-A-3 148 062; US-A-3 227 554; US-A-3 384 657; US-A-3 379 529; US-A-3 615 506; US-A-3 617 291; US-A-3 620 746; US-A-3 701 783; US-A-3 733 201; US-A-4 049 455; US-A-4 095 984; US-A-4 126 459; US-A-4 149 886; US-A-4 150 228; US-A-4 211 562; US-A-4 248 962; US-A-4 259 437; US-A-4 362 878; US-A-4 409 323; US-A-4 477 563; US-A-4 782 012; US-A-4 962 018; US-A-4 500 634; US-A-4 579 816; US-A-4 607 004; US-A-4 618 571; US-A-4 678 739; US-A-4 746 600; US-A-4 746 601; US-A-4 791 049; US-A-4 857 447; US-A-4 865 959; US-A-4 880 342; US-A-4 886 736; US-A-4 937 179; US-A-4 946 767; US-A-4 948 716; US-A-4 952 485; US-A-4 956 269; US-A-4 959 299, US-A-4 966 835; US-A-4 985 336 as well as in British patent specifications 1,560,240; 2 007 662; 2 032 914; 2 099 167; German specifications 2 842 063; 2 937 127; 3 636 824; 3 644 416 as well as the following European Patent Publications: 0 272 573; 0 335 319; 0 336 411; 0 346 899; 0 362 870; 0 365 252; 0 365 346; 0 373 382; 0 376 212; 0 377 463; 0 378 236; 0 384 670; 0 396 486; 0 401 612; 0 401 613.

Such compounds are also disclosed in "Developer-Inhibitor-Releasing (DIR) Couplers for Color Photography" C.R. Barr, J.R. Thirtle and P.W.

Vittum in Photographic Science and Engineering, Vol.

13, p. 174 (1969).

Generally, the developer inhibitor-releasing (DIR) couplers include a coupler moiety and an inhibitor coupling-off moiety (IN). The inhibitorreleasing couplers may be of the time-delayed type (DIAR couplers) which also include a timing moiety or chemical switch which produces a delayed release of inhibitor. Examples of typical inhibitor moieties are: oxazoles, thiazoles, diazoles, triazoles, oxadiazoles, thiadiazoles, oxathiazoles, thiatriazoles, benzotriazoles, tetrazoles, benzimidazoles, indazoles, isoindazoles, mercaptotetrazoles, selenotetrazoles, mercaptobenzothiazoles, selenobenzothiazoles, mercaptobenzoxazoles, selenobenzoxazoles, mercaptobenzimidazoles, selenobenzimidazoles, benzodiazoles, mercaptooxazoles, mercaptothiadiazoles, mercaptothiazoles, mercaptotriazoles, mercaptooxadiazoles, mercaptodiazoles, mercaptooxathiazoles, tellfeurotetrazoles or benzisodiazoles.

These two couplers act in different ways to create a constant density in the unwanted spectral region of any imaging dye regardless of the amount of that image dye formed and thereby improve the colour reproduction in the final photograph.

For example, in the case of the cyan imaging.

dye discussed above, a magenta-coloured. masking -coupler can be added to the cyan imaging layer. This coupler is pre-coloured magenta before development but the magenta colour is progressively reduced or destroyed as the cyan dye from the main imaging coupler is formed. As a result the total green density from the unwanted absorption of the cyan dye and magenta masking coupler sum to a near constant value regardless of the amount of red density. Colour reproduction is improved because the layer only modulates red light during the printing step.

Alternatively, a similar result can be achieved by adding a DI(A)R coupler to the cyan imaging layer. This acts to improve the colour reproduction performance of the film by reducing the amount of magenta image dye in a nearby magenta imaging layer as a function of the amount of cyan dye formed. The reduction in the amount of magenta dye formed in the nearby layer is balanced to approximately equal the amount of unwanted green absorption of the cyan dye formed.

Naturally, a colour negative film may incorporate both types of couplers in some of the layers where appropriate.

Problem to be solved by the Invention However, both masking couplers and DI(A)R couplers are expensive and add considerably to the cost of the colour negative film.

Moreover, it is not possible to use masking couplers in the yellow imaging layer as this reduces the sensitivity of the underlying green-sensitive layer.

Furthermore, effluent from processing of colour film materials may be pollutants. The composition of the film has an effect on-the amount of these pollutants generated during processing. In particular, iodides in the film are difficult to deal with in the processing stage as they slow down the fixing rate. In order to compensate for the slow fixing rate, ammonium and/or thiocyanates are used to increase the fixing rate.

High concentrations of thiosulphates can also be used to increase the fixing rate. However, this leads to increased amounts of undesirable chemicals in the effluent from the process.

However, films made with silver halides containing lower levels of iodides are less responsive to the DI(A)R couplers currently used.

This means that another method of colour correction is needed.

Summary of the Invention It is therefore an object of the present invention to provide a method of correcting the colour, particularly in colour negative film, which overcomes the problems mentioned above.

In accordance with one aspect of the present invention, there is provided a method of correcting for unwanted colour absorption in at least one image dye layer of a colour negative film having an image of a scene recorded thereon, the method comprising the steps of: developing the image of the scene; re-exposing the developed image with light having spectral characteristics similar to that of the unwanted colour absorption of the image dye layer, the film being exposed from at.least one side such that the layer sensitive to this light is masked by the image formed in that layer whose unwanted colour absorption is being corrected; and further developing the film to form a masked image of the scene.

Advantageous Effect of the Invention By this method, the adverse effects of the unwanted absorptions of the dyes forming the image can be removed or substantially reduced.

Moreover, the method of the present invention allows for colour correction either without the need for expensive masking and/or DI(A)R couplers or by using less of these expensive materials.

Furthermore, the method according to the present invention is particularly useful with colour negative films made with silver halide emulsions which are less responsive to DIR couplers, and as a result, provides a novel alternative method for improving the colour correction for such films.

Brief Description of the Drawings For a better understanding of the present invention, reference will now be made, by way of example only, to the accompanying drawings in which: Figure 1 is a schematic illustration of a typical multilayer colour negative film; Figure 2 is a schematic illustration of a developed image formed in the cyan imaging layer of the film shown in Figure 1; and Figure 3 is similar to Figure 2, but illustrating the film after re-exposure and development.

Detailed Description of the Invention The present invention will be described in relation to a typical multilayer colour-negative film and in particular for unwanted green light absorption of cyan imaging dye. Naturally, the present invention could equally be used to correct other selected unwanted absorptions.

Figure 1 shows a typical multilayer colour negative film 10 which comprises a support substrate 12, imaging dye layers 14, 16, 18, and a protective layer 20. (It is to be noted that the term "layer" is not limited to a single layer, but may comprise more than one layer.) As shown, imaging dye layer 14 consists of a blue-sensitive, yellow dye image forming layer coated over the top of imaging dye layer 16, a green-sensitive, magenta dye forming layer, which in turn is coated over the top of imaging layer 18, a red-sensitive, cyan dye forming layer.

When the film is exposed to light from a scene, images are formed in one or more layers according to the colour content of the exposing light.

However, for simplicity, the invention will be described with reference to a single imaging dye layer, the cyan imaging dye layer 18.

According to the method of the present invention, the adverse effect of the unwanted green absorption of the cyan image dye on the colour fidelity of the subsequent reproduction is reduced by creating a reverse scale in an adjacent magenta dye forming layer.

This is achieved by first developing the film which has been exposed to some red light in a scene but without bleaching or fixing the image formed thereon.

Figure 2 shows the developed images formed in the cyan imaging layer of the film 10 after exposing a portion 30' of the film 30 to the red light 'R', portion 30" remaining unexposed, and development of the entire film.

As before, the film 30 comprises a support substrate 32 and a protective layer 40 with imaging dye layers 34, 36, 38 therebetween. Layers 34, 36, 38 correspond to respective layers 14, 16, 18 as described with reference to Figure 1.

In the portion 30' of the film 30 which has been exposed to red light, cyan image dye 38a' (schematically shown as solid circles) is formed in the cyan imaging layer 38'. A developed but unbleached silver image 38b' (schematically shown as solid triangles) is also formed in the cyan imaging layer 38'. Unwanted absorptions are also present in the cyan imaging layer 38'.

In the portion 30" of film 30 which is unexposed, undeveloped coupler 38a" (shown schematically as circles) and undeveloped silver halide 38b" (shown schematically as triangles) are present in the cyan imaging layer 38".

The near neutral coloured, developed silver image 38b' is then used as a mask to form the reverse image of the cyan record in the adjacent magenta imaging layer 36. This is done by re-exposing the entire film 30 with a controlled, uniform, low intensity green flash 'G' (as shown in Figure 3) through the support substrate 32 and then redeveloping the film thus exposed. The result is shown in Figure 3.

In Figure 3, the magenta dye 36a' and the developed silver image 36b' formed in the magenta imaging layer 36' as a result of the re-exposure and redevelopment are shown schematically as solid circles and triangles according to the convention used before.

The undeveloped coupler 36a and silver halide 36b are also shown as circles and triangles as before.

As a result of the green flash exposure, magenta dye 36a' is formed in the adjacent layer 36' during the second development stage together with the corresponding silver image 36b'. The magenta dye 36a' and the corresponding silver image 36b' are formed where there is little or no cyan record in the cyan imaging layer 38.

After the second development stage, the film can then be bleached and fixed as usual.

The amount of magenta dye formed during the second development stage can be further controlled by the intensity of the green flash exposure and the extent of the second development stage itself.

In this way, the amount of unwanted green absorption of the cyan imaging dye formed in the first development stage can be counterbalanced by the amount of magenta dye formed in the second development stage.

It is to be noted that the second development stage will allow development to continue in all layers of the film. Therefore, as well as forming the desired mask images, development will also continue in the layers whose images are being corrected.

In order to obtain the best overall colour reproduction, the development times in both the first and second development stages, together with the levels of uniform flash re-exposure, must all be adjusted to achieve the best balance of primary and masked images.

A specific example where the method according to the present invention is useful is in saturated colour situations. For example, if a photograph is taken of a red bus, the red masking of the green-sensitive layer in the negative-using the technique described above will filter out the unwanted green absorptions in the negative to enable a red bus to be printed from that negative.

The present invention is particularly useful with colour negative films made with emulsions containing lower levels of iodide and more bromide or chloride.

The present invention is even more useful for films made with emulsions without any iodide at all, such as pure bromide, chlorobromide or chloride emulsions which are much less responsive to DI(A)R couplers.

The invention is particularly useful for colour films which are processed in processing apparatus of the type described in co-pending British patent application no. 9307504.2 entitled "Photographic Processing Apparatus" filed on 13 April 1993 (now European patent application no.

In such apparatus, the film being processed can be readily transported from an upstream processing stage back to a downstream processing stage.

Processing apparatus of this type automatically provide for two development stages and could easily be adapted to provide the controlled, uniform flash reexposures needed for the method of the present invention.

Thus, a preferred version of such apparatus would provide for film to be transported, after the first development stage, past uniform, low intensity re-exposing flash devices before being transported back into the developer tank for the second development stage.

Although, the present invention has been described with reference to the correction of the unwanted green light absorption of the cyan image dye of a typical colour negative film, similarly, any unwanted green light absorption of the yellow image dye could be overcome by using a controlled, uniform, low intensity green flash exposure through the top (yellow) layer in a typical film, after the first development and before the second development stage.

Some unwanted red absorptions of the magenta and/or yellow dyes could also be overcome by using a controlled, uniform, low intensity red flash exposure through the top of the film after the first development stage and before the second development stage.

However, in this case, for the typical film structure described above, a red flash exposure through the top of the film may cause a reverse scale of both the magenta and yellow images created in the first development. In that case, it would not allow separate corrections of the unwanted red absorption of the magenta and yellow image dye layers.

Furthermore, some unwanted blue absorption of either the magenta and/or cyan dyes of such a film could be similarly overcome by using a controlled, uniform, low intensity blue flash exposure through the film support, after the first development and before the second development stage. However, if the magenta forming layer is sensitive to blue light, then the correction of the unwanted blue absorption of the red layer cannot be carried out independently of other corrections.

Although colour correction for a single unwanted colour absorption of an image dye is described above, it is to.be understood that more than one correcting re-exposure can be simultaneously carried out. For example, correction for both unwanted red and green absorptions can be simultaneously carried out by applying controlled uniform exposures through the top of the film and through the bottom respectively.

The invention has been illustrated above for a typical multilayer colour film with a particular layer structure. However the procedure can be used for any multilayer colour film with any layer structure as long as the re-exposure flash is given from the correct side of the film such that the flash is modulated by the near neutral silver image in the layer with unwanted absorptions before it exposes the mask forming layer.

A preferred colour negative film would contain an anti-halation undercoat consisting of dyes which are removed or destroyed during the first development stage.

Claims (4)

CLAIMS:

1. A method of correcting for unwanted colour absorption in at least one image dye layer of a colour negative film having an image of a scene recorded thereon, the method comprising the steps of: developing the image of the scene; re-exposing the developed image with light having spectral characteristics similar to that of the unwanted colour absorption of the at least one image dye layer, the film being exposed from at least one side such that the layer(s) sensitive to this light is masked by the image formed in that layer whose unwanted colour absorption is being corrected; and further developing the film to form a masked image of the scene.

2. A method of correcting for unwanted- colour absorption in at least one image dye layer of a colour negative film comprising a support substrate (12; 32) on which a plurality of image dye layers (14, 16, 18; 34, 36, 38) are formed in ascending order from the substrate (12; 32) of at least one red-sensitive, cyan dye forming layer (18; 38), at least one greensensitive, magenta dye forming layer (16; 36) and at least one blue-sensitive, yellow dye image forming layer (14; 34), the method comprising the steps of: developing the image of the scene; re-exposing the developed image with light having spectral characteristics similar to that of the unwanted colour absorption of the at least one image dye layer, the film being exposed from at least one side such that the layer(s) sensitive to this light is masked by the image formed in that layer whose unwanted colour absorption is being corrected; and further developing the film to form a masked image of the scene.

3. A method according to claim 2, wherein correction for unwanted green absorption in the cyan dye forming layer (16; 36) is carried out by reexposing the film through its substrate (12; 32).

4. A method according to claim 2 or 3, wherein correction for unwanted green absorption in the yellow dye forming layer (14; 34) is carried out by re-exposing the film from the top of the film.