GB2034060A - Treatment of an Exposed Photographic Film to Increase the Effective Speed Thereof - Google Patents

Abstract

A process of treating an exposed photographic film to increase the effective speed thereof, comprises: developing the film to produce a reduced silver image and fixing the film; re-halogenating the reduced silver image to convert the silver to a soluble silver complex; and re- developing the film in a colour- coupling developer in the presence of colour-coupling dye units. After the re- developing of the film silver units produced during the re-developing may be removed. The film may be of the black-and-white negative type or of the colour reversal or negative type. The process enables the effective speed of exposed photographic film to be greatly increased with minimal sacrifice of quality and exposure latitude and with very substantial boosting or amplification of threshold image-recording near the toe of the density versus log of exposure characteristic curve.

Description

SPECIFICATION Treatment of an Exposed Photographic Film to Increase the Effective Speed Thereof The present invention relates to photographic film processing, being concerned with processes for increasing the effective "speed" of such films (defined in terms of the minimum energy required to record a detectable image).

The primary ways in which photographic films have heretofore been rendered more sensitive or of increased speed, are as follows. First, the size of the silver halide crystals in the light-sensitive emulsion has been increased to increase the probability of photon absorption. Secondly, the crystals may be chemically sensitized during preparation to increase the efficiency of electrontrapping, as electrons are released upon photon impact. Thirdly, in the processing, more efficient reducing agents have been employed to discriminate between exposed and non-exposed crystals.

One of the common methods of rating the photographic speed of film is in terms of the minimum camera exposure required to produce a recorded threshold image. This is expressed in terms of relative ASA speed ratings, the values of which increase in correspondence with increases in the speeds of films. Present-day techniques permit ASA ratings of the order of 2000 for very high-speed black and white negative films, and of the order of 400-500 for high-speed reversal colour films. In order to increase the effective speed of the negative type film, prolonged development may be employed to increase the slope of the density versus log of exposure characteristic curve (D-Log E) near the toe of the curve, but with a sacrifice of quality in the reduction of the available exposure range or latitude and fogging.Factors of two to three in effective speed increase can, however, thus be obtained. Forced development of reversal colour films will also produce an apparent increase in speed, for strong images, but actually no increase in the image-recording threshold at the toe of the D-Log E curve or the shoulder of its reversal curve.

Underlying the present invention, however, is the startling discovery of a process with which black and white negative, colour reversal and negative films and the like can be processed to increase their effective speeds to degrees previously unattainable, and with minimal sacrifice of quality and exposure latitude, and with very substantial boosting or amplification of threshold image-recording in the two of the D-Log E characteristic. This has opened up new opportunities in photo-instrumentation, particularly in underwater applications, as in peatstained lakes, where light attenuation may be severe and the range of photography most limited.

An object of the invention, accordingly, is to provide a process for increasing the effective speed of photographic films that is not subject to the above-described limitations of prior techniques.

In accordance with the present invention, there is provided a process of treating an exposed photographic film or the like (hereinafter referred to as "film") to increase the effective speed thereof, comprising: developing the film to produce a reduced silver image and fixing the film; re-halogenating the reduced silver image to convert the silver to a soluble silver complex; and re-developing the film in a colour coupling developer in the presence of colour coupling dye units.

There is provided, in accordance with a preferred aspect of the invention, a process for increasing the effective speed of a photograhic film and the like (hereinafter referred to as film), that comprises: developing an exposed film with black and white developer and fixing the same to isolate the exposed photosensitive film crystals as a reduced silver image; re-halogenating said reduced silver image to convert the same to a soluble silver complex; re-developing the film in a colour-coupling developer in the presence of colour-coupling dye units to reduce the image to silver units and proximal colour units with multiple colour units for each silver unit; converting the silver units to a soluble silver complex; fixing the film to remove all traces of the silver; and washing and drying the film.

The invention is illustrated by the following examples.

Example 1 Turning, first, to the application of the invention to black and white negative film, it will be recalled that the D-Log E characteristic curve shows a long, just slightly rising, almost horizontal toe emerging into a constant steep slope region which then shoulders off in saturation. The threshold of image recording lies within the almost horizontal toe. While, as before stated, prior techniques of forced development will somewhat tilt the toe upward to provide a lower effective image-recording threshold, this is limited by the inherent development of all silver-halide crystals (whether exposed or not) and the consequent fogging with resultant loss in effective overall film speed.

In accordance with the invention, the black and white negative film (such as Eastman [Registered Trade Mark] Recording Film 2475) is first forcedeveloped in conventional black and white developer (such as phenyl methyl pyrazolidone) to produce maximum speed with minimum fog. It has been found to be preferred for the purposes of the invention that the temperature be maintained cool, around 750F, and the time of the developing of the order of 12 minutes. The film is then fixed by dissolving out the undeveloped silver halide crystals, as with sodium thiosulphate, leaving only the final reduced silver image. Following washing, the reduced silver image is completely converted to a soluble silver complex by re-halogenation with a bleaching agent, such as potassium fern cyanide.

After washing, the film is re-developed, but this time in a colour-coupling developer such as 4amino-N-ethyl-N-(B methanesulphonamidoethyl)m-toluidine sesquisulphate monohydrate (sold, for example, by Eastman Kodak under type "Color Developing Agent CD-3"), to which has been added a colour-coupling agent such as 2,4dichloro-1 -naphthol (cyan or blue-green), or any similar desired colour dye. This re-developing stage is allowed to proceed to completion (of the order of about eight minutes at room temperature), reducing the image to silver and, in this case, blue-green colour dye proximal to the silver. The colour-coupling developer is removed by washing, and the silver is again completely converted to a soluble silver complex with the above-mentioned re-halogenation bleaching agent, following which the film is fixed; as before described, this time to remove all traces of silver.

The film is then washed and dried.

It has been found that this process enables undetectable images in the film after the first development step, now to be clearly indicated, this time in the colour of the colour-coupling agent. Otherwise stated, the threshold of detectable image-recording has been markedly lowered, with the image manifesting itself by the colour dye. What appears to have happened is that, if the right proportions are used, each exposed silver unit can be replaced by a number of colour dye units; multiple dye units being more visible than a single silver unit that they replace.

In the above example, 6 units of colour coupling agent were used for every 2 units of the CD-3 colour-coupling developer, producing an image speed increase of a factor of four, Such proportions represent, of course radical departures from those used for other objectives in usual colour film development (such as 3 units of CD-3 for 2 units of colour coupling agent, as in Kodak's "Kodachrome" developing procedures).

Returning to the D-Log E curve, the almost horizontal toe, representing few exposed silver units, has been effectively turned upward with a greater slope corresponding to this amplification or effective enhancement, and thus providing an effective increase in photographic film speed, without the relatively rapid fogging density effect in ordinary prior prolonged development processes, before mentioned.

By this technique, the exemplary 2475 film ASA rating of about 2000 has been startingly boosted to about 8000 and above, even up to ASA ratings of the order of 20,000.

Example 2 The steps of Example 1 were repeated, but increased contrast for the faintest images were obtained by then re-cycling or repeating the soluble silver complex/colour-coupling redeveloping and subsequent steps. The contrast was found to be approximately doubled with the re-cycling procedure.

Example 3 In this example, colour film, (Kodak "Ektachrome" [Registered Trade Markj VNX, ASA 400) was successfully rendered as a colour negative and provided with greatly increased speed by the process of the invention.

The exposed colour film was first developed in a black-and-white phenyl methyl pyrazolidone developer (about 5 minutes at 70oF) and then fixed to produce a black and white negative. After washing, the reduced silver image was converted completely to a soluble silver complex as in Example 1.

Following washing, the film was re-deveioped, this time in the colour-coupling developer of Example 1, but without the addition of the colourcoupling agent in view of the presence of colourcoupling dye units already incorporated in each layer of the film.

The silver was again converted to the soluble silver complex by the re-halogenating bleaching agent of Example 1, and the film was fixed, washed and dried, resulting in a full true colour negative image with vastly increased speed.

By re-cycling the soluble silver complex/redeveloping and bleaching or re-halogenating and fixing steps, an ASA of 20,000 was attained, Photographs taken by strobe lighting of objects at distances of the order of thirty feet in the heavy peat-stained waters of Loch Ness, Scotland, and completely undetectable in the black and white negative stage, became for the first time readily apparent in the colour negative thus processed.

There are instances, moreover, such as where colour discrimination is not important, wherein the silver units may be kept in the developed product together with the proximal colour units achieved by the colour-coupling developer redeveloping step. An example of such follows as: Example 4 The steps of Example 1 were repeated up to and including the re-development in the colourcoupling developer CD-3 with the added cyan colour-coupling agent. The colour-coupling developer was then washed and the film was then dried.

This could be re-halogenated with a re-cycling of the colour-coupling developing step to attain even greater gain as contrast.

While the invention has been described in connection with particular examplary films, it is to be understood that the process is equally useful with other films of similar or related characteristics.

Claims (26)

Claims

1. A process of treating an exposed photographic film or the like (hereinafter referred to as "film") to increase the effective speed thereof, comprising: developing the film to produce a reduced silver image and fixing the film; re-halogenating the reduced silver image to convert the silver to a soluble silver complex; and re-developing the film in a colour coupling developer in the presence of colour coupling dye units.

2. A process according to claim 1, further comprising, after the re-developing of the film, removing silver units produced during the redeveloping.

3. A process according to claim 2, wherein the silver units are removed by converting them to a soluble silver complex and then fixing the film.

4. A process according to any of claims 1 to 3, wherein the film is of the black-and-white negative type and a colour coupling dye agent is added to the colour coupling developer to provide the colour coupling dye units.

5. A process according to any of claims 1 to 3, wherein the film is of the colour reversal or negative type, the colour coupling dye units being present in the film before exposure thereof.

6. A process according to any preceding claims, wherein the re-halogenating step is effected by bleaching.

7. A process according to claim 3 or any of claims 4 to 6 as appendent to claim 3, wherein the converting step is effected by bleaching.

8. A process according to any preceding claim, wherein, after the last-mentioned re-developing step, the re-halogenating and re-developing steps are repeated at least once.

9. A process according to any preceding claim, wherein in the re-developing step the image is reduced to silver units and proximal colour units with multiple colour units for each silver unit.

10. A process of treating an exposed photographic film or the like (hereinafter referred to as "film") to increase the effective speed thereof comprising: developing the film with black and white developer and fixing the same to isolate the exposed photo-sensitive film crystals as a reduced silver image; re-halogenating said reduced silver image to convert the same to a soluble silver complex; re-developing the film in a colour-coupling developer in the presence of colour-coupling dye units to reduce the image to silver units and proximal colour units with multiple colour units for each silver unit; converting the silver units to a soluble silver complex; fixing the film to remove all traces of the silver; and washing and drying the film.

1 1. A process according to claim 10, in which, following the last-mentioned fixing step, the rehalogenating, re-developing and converting and fixing steps are repeated.

12. A process according to claim 10 or 1 1, in which said re-halogenating and converting steps are effected by bleaching.

13. A process according to any of claims 10 to 12, in which the film is of the black and white negative type, and the presence of colourcoupling dye units in the re-developing step is effected by adding a colour-coupling dye agent during the re-developing step; the finally developed film recording the image in the colour of said agent.

14. A process according to any of claims 10 to 12, in which the film is of the colour type renderable as a colour negative, and the presence of colour coupling dye units in the re-developing step is effected by the colour-coupling dye units already incorporated in the film layers.

15. A process according to any preceding claim, wherein the black-and-white developing is effected with phenyl methyl pyrazolidone as developer.

16. A process according to any preceding claim, wherein the fixing is effected with sodium thiosulphate as fixer.

17. A process according to any preceding claim, wherein the re-halogenating is effected with potassium ferri-cyanide as bleaching agent.

18. A process according to any preceding claim, wherein the re-developing is effected with 4-amino-N-ethyl-N(B methanesulphonamidoethyl)-m-toluidine sesquisulphate monohydrate as developer.

19. A process of treating an exposed photograhic film or the like to increase the effective speed thereof, comprising: developing and fixing the black-and-white image corresponding to the exposed silver halide film crystals as a reduced silver image; rehalogenating the image to convert the same to a soluble silver domplex; re-developing the film in a colour-coupling developer in the presence of colour-coupling dye units; and removing the silver units to provide an image of colour units that enables an increase in detectable image in a colour over that provided by the silver units in black and white.

20. A process of treating an exposed blackand-white film or the like to increase the effective speed thereof, comprising: developing and fixing the black-and-white reduced silver image, redeveloping the film in a colour-coupling developer in the presence of colour coupling dye units and replacing the silver in the image with the colour dye units to enable a colour image enhanced over that provided by the silver image.

21. A process according to claim 20, in which the re-developing and replacing steps are recycled.

22. A process of treating an exposed colour film having colour dye units in the film layers and renderable as a colour negative to increase the effective speed thereof, comprising developing and fixing the black-and-white reduced silver image, re-developing the film in a colour-coupling developer and replacing the silver in the image with the colour dye units to provide an enhanced colour image.

23. A process according to claim 22, in which the re-developing and replacing steps are recycled.

24. A process of treating an exposed photographic film or the like to increase the effective speed thereof, comprising: developing the film with black and white developer and fixing the same to isolate the exposed photosensitive film crystals as a reduced silver image; rehalogenating said reduced silver image to convert the same to a soluble silver complex; re developing the film in a colour-coupling developer in the presence of colour-coupling dye units to reduce the image to silver units and proximal colour units with multiple colour units for each silver unit; and washing and drying the film.

25. A process as claimed in claim 24 in which, following the re-developing step, the re halogenating and re-developing steps are cycled.

26. A process according to claim 1, substantially as described herein in any of Examples 1 to 4.