CA2046626A1

CA2046626A1 - Photographic processing

Info

Publication number: CA2046626A1
Application number: CA002046626A
Authority: CA
Inventors: Christopher Barrie Rider
Original assignee: Individual
Current assignee: Eastman Kodak Co
Priority date: 1989-02-01
Filing date: 1990-02-01
Publication date: 1990-08-02
Also published as: GB8902186D0; JP2930407B2; ES2054339T3; MY104823A; EP0456684A1; ATE107050T1; WO1990008979A1; KR920701866A; DK0456684T3; AU627551B2; AU5021890A; JPH04503121A; EP0381502A1; DE69009741T2; EP0456684B1; DE69009741D1

Abstract

In known photographic processing apparatus, quality of the photographs produced can be adversely affected by drift in the paper processor of the apparatus. One cause of drift is incorrect replenishment of the chemicals used in the paper processor. In processing apparatus which utilise only small volumes of chemicals, drift can be caused by replenishment rates not matching the dye formed on the prints being processed, and an operator would need to take steps to adjust the processor. Described herein is an improved method of controlling the replenishment rate of chemicals in photographic processing apparatus. The method comprises deriving a control signal from the image to be exposed on to photographic material and using the derived signal to control the replenishment rate of the chemicals.

Description

~ ~ 90/08979 2 0 4 6 ~ 2 ~ Pcr/GBgo/oolfi2 PHOTOGRAPHIC PROCESSING
The present invention relates to the replenishment of chemical solutions used in the processing of photographic materials.
In a photo~inishing laboratory, one of the prob]ems which must be overcome if quality standards are to be maintained concerns the drift in the sensitometry of processed photographic materials.
One cause of such drift is incorrect replenishment of ohemicals. As the chemicals in the processor baths are used up, replenishment chemicals must be added to the baths in order to keep the activities and concentrations of the chemicals constant.
Most modern paper processors use detectors at the input to measure the area of paper passing into them. Replenishment rates can then be derived assuming that, on average, the p~per has been exposed to a mid-grey. This assumption is reasonable, considering that most printers use an 'lintegrate-to-grey" system.
Many modern printers; however, also have colour correction levels different from 100% and slope ` correction, which together will cause deviations from the "integrate-to-grey" assumption. These density and colour-balance deviations may not signiEicantly aEfect ; the operation of a processor with bflths containing l~rge volumes o~ chemicals. However, a small processor would be more susceptible to dr$ft due to replenishment r~tes not compenqatlng for the amount of dye ~ormed on the paper being processed. At this polnt an operator would take steps to bring the proce~sor b~ck to aim.
GB-A-2111726 describes a system ~or controlling the addition of replenisher to a bath in which light~sensitive media are being processed. The signal controlling the rate of addition o~ replenisher .. ..

WO90/0$979 ~ p~r/GBso/oo162 chemicals i9 derived fro~ the area of the light-sensitive media which has been scanned by a laser exposing device.
lt is therefore an ob,ject of the present invention to provide an improved method of controlling the rate of addition o~ replenLsher chemicals to a pho~ographic processor.
In accordance with the present invention, - there is provided a method of controlling the rate of ~eplenishment of chemical ~olutions used in photographic processing apparatus, the apparatus including photographic printing apparatus for copying an object on to photographic material, the method heing characterized by the steps of deriving a signal which is related to the exposure given to the photographic material, an~ using the signal to control the replenishment rate o~ the processing solutions.
Preferably, the derived signal produces a replenishment rate which is directly related to the amount of image--producing substances formed on the photographic m~terial a~ter development of an image of the object.
Advantageously, the derived signal produces a replenishment rate which exactly balances the ~5 chemicals depleted in processing the photographic material.
Photographic processors are normally set up so that the replenishment rate exactly compensates for the chemicals used ln processing paper which hss been expo~ed to an predefined sverage grey level. This grey level is intended to simul,~te the a~ount of dye produced on R print mflde from the average (population centre) customer negative. It ls usual to calibrate the printer with quch fl populstion centre negatlve which is printed tG produce a grey print at the average g~ey level. The printer i9 adjusted so that the correct density is produced on the grey print.

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~ 90/(~8979 _3 20~ Pcr/G~ ol62 Having calibrated the printer in this way, the factory calibration of the replenishmen~ system of the processor will also be correct since the average of all prints will turn out to be the sverage grey level produced by the printer c:alibration.
The notion o~ ~ popul~ltion centre negative is a use~ul although fictitious one, since there are always large statistical fluctu~tions in the negatives submitted by customers. As mentioned earlier, ~or large volume mschines, fluctuations ~ill give rise to little concern. For machines with very small tank volumes, however, this will not be true.
In the following discussion, a method for replenishing photographic developer solution will be described as a particular example. However, t~lis method could be ~pplied to any process where the chemicals are used up according to some function of the amount of exposure given to the material, rather than by khe area of exposed material being processed.
The equations derived below m~y need to be modified accnrding to the exact nature of the process involved.
A colour photographic material has three image forming layers: the cyan, magenta and yellow.
Light is pro~ected through the film on to the paper to form a latent image which is rendered visible by the processing solutions. Dye is formed by the resction of developer molecules which have been oxidised by the reduction of silver hslide to silver ~etal and halogen g~s, with coupler molecules in the paper. The equivalence of a dye is the ~mount of oxidised devèloper molecules which is needed to form one moIecule of the dye. In photogrAphic paper, the dyes used flre typieally 2 and 4 equivalent. In practice, the measured equivalence of a dye may be more th~n this be~ause not ~11 oxidised developer molecules are converted to dye. Some molecules are lost due to other reactions snd processe~. Furthermore, the .

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amount of oxidised developer molecules that are lost may vary ~ccording to the amount of dye which has already been formed on the paper at any p~int in the development cycle.
Let the amount of dye formed in the cy~n layer of one square foot of paper be c, the amount in the m~genta layer be m, ~nd the amount in the yellow layer, y, all ln grams. A genersl expression for the weight of developer replenisher which must be added to the developer tank to replace the developer which has been used to process 1 square foot of colour paper, R, is R-k[ec(c)+em(m)~ey(y)~i(t)]+K ............ (1) where k is a constant of proportionality;
ec, em, and ey are functions of the dye amounts c, m and y, respectively;
; is a function of time, t, and represent~
the natural process of degradation of the developer by, for example, aerial oxidation, and is dependent on the design of the processor tank; and K is a constant representing the weight of developer carried out o~ the tank by the wet paper -25 after development.
Consider now an expression for the average amount of replenisher added per ~quare foot of p~per RSsUming that the paper has been exposed to an average grey as de3cribed above in rel~tion to printer calibration. The superscript is used to denote an average. In the following expression, therefore, R
ls the ~versge flmount of repleni~her which is ~dded per squ~re foot of paper.

R-X[ectc)~em(mj+ey(y)~t)]+K ........ (2) ~O90/OB979 PCT/GB90/00162 ~, -5- - `

2 ~ 2 ~
By subtracting equation (2) from equation (1), we obtain the following expression for the dirference in replenisher, ~R, which must be added : compared to the average amount to correct for varia~ions in the dye amounts for each square ~oot of paper entering the printer, ~R=k[ec~c)~em(m)~ey(y~-K] .......... (3) where K=k[ec(c)+em(m)+ey(y)] ........... .(4) K is a known quantity and is a recommended figure by manufacturers oE photographic products. For machines with large tank volumes, there will be as many prints with dye amounts less than the average than with dye amounts above the average. Developer efficiency is therefore unaffected by these 20 fluctuations in print dye amount. Small volume machines, however, would benefit from being able to calculate ~R and vary the replenlsher rates accordingly. There are several ways of calculating ~R, but none is perfectly accurate.
It is the object of the present invention to deseribe the principles involved and techniques which could be used to determine ~R, as opposed to the - exact detail of formul~e etc. It ~hould ~l~o be borne in mind that the ~verage repleniqhment rate assu~ption currently in use is extremely effective. This invention provides ~ small correction to this technique and absolute eccuracy is there~orP
unnecessary, though accur~cy becomes increasingly important as t~nk volume is reduced. A further complexity which should be understood is that the exact nature of the functions for dye equivalence will vary between different manufacturers' p~pers.

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WOgO/08979 ~ PC~/Cn~0/00162 ; - 2~ b -6- ~ l The .simplest approach to this problem is an empirical one. Most photofinishing printers work on the "integrate-to-grey principle" (see 'The Reproduction of Colour', 4th Eclition, Fountain Press, Hunt R W G, at section 16.7 on page 294) or a more sophisticated variant of it. In essence this means that the printer tries to print each negative to produce the ~ame amount of dye on the print, though some more sophlsticated exposure determination algorlthms may diverge from this when printlng "difficult" negatives like snow scenes or fireworks shots. It is possible to override this tendency by using a manual correction to the exposure time. The corrections are usually defined in terms of "density button" units where each button adds a fixed increment to the exposure time, typically 19%. Thus a '~3 but~on' correction increments the time by 1.19 x 1~19 x 1.19 or 1.68. A '-4 button' change decreases the time by 1.19 x 1.19 x 1.19 x 1.19 or 2 (a halving of - 20 the time). The exact increment is usually variable and can be set llp by the user.
If the amount of replenisher which mus~ be added to the developer tank per square foot of paper printed normally (without manual correction) is known, it is possible to calculate the amount of dye which will be formed on a print which has been correctPd for density. The calculation is not trivial ~nd will be addre~sed later. It i5 nevertheless poRsible, whether by experiment or by calculation, to ~ssign to each correction button, an ~djust~lent to the replenishment rate sccording to the difference in dye formed on the print. This is equivalent to solving equ~tlon t3) ~bove ~t diRcrete values of c, m ~nd y.
~or ex~mple, we might find that for Q ~4 correction to a print, there is 1.75 times us much dye produced ln each of the three layers ~s for a nnrmal print. Thus 1.75 times as much replenisher would need to be added .

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~090/08979 PCT/~0/00~62 20~6~2~
as for a normal print.
In this way the replenishment rate may be varied without the need for cornplicated calculations.
Implementation is therefore cheap and si~ple, S requiring only the use of a lookup table referencing ~R to each correction button. The same principle may also be applied to the colour correction buttons, though it should be understood that the dye equivalency functions may not be the same for each layer.
More sophisticated printer algorlthms may permit much smaller lncrements in density and colour balance. In these c~ses, lt may be possible to perform a calculation to get values for ~R rather than having ~o perform many experimental determinations. Again, the exact details of the calculation will vary from machine to m~chine so the general outline will be explained below, where the assumption is made that an average me~surement of the negative transmittance has been made (rather than discrete measurements at many places on the negative).
Each printer has some form of exposure determination algorithm whose output is an exposure, Ei, to each of the three layers ti = c, m and y) of a pho~ographic paper relative to some calibration setting, Ei.
There is ~ well known rel~tion between exposure snd optical reflection density, RDi, known RS the RD ~ log(E) curve for each l~yer of the paper which can be u-~ed to calcul~te the optic~l density of the print in e~ch layer. This relation i9 discu3sed in 'The Theory of the Photogr~phic Process', 4th edition, Mees C.E.K. and JRme~ T.H., p~ge 529.
The next ~tep i5 to convert from reFlection density to tr~nsmission densi~y using ~nother well known relation (see Willlams and Klapper, Journal of the Optical Society of America, 1953, volume 43, page .

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, --8- PCI/GB90/00162 595). It is now possible to obtain relative dye amounts on the print to a good approx~mation by taking the ratio o~ the transmission densities of the print in question, TDi, to the transmission density o~ the - 5 calibration print, TDi. We may there~ore write for the m~genta l~yer for example, m T
= _ ............................................ (5) m TDl If the contribution from the magenta layer ~o the total repleni.shment needed for the print is Rm and that for the calibration print is Rm, then we may write, Rm TDi ~ (6) Rm TDi and more generally, Ei ~Ri = Ri ( - - 1 ) ..... (7) Ei In equation (7), we have a relationship between the correction to the replenishment rate and the tr~nsmisslon density of the print, which is 8 function o~
Ei, the expo~ure given to the print. The functional relativnship between TDi snd Ei is found from ~
knowledge of the p~per's RD - log(E) curve, and the RD/TD cur~e fl~ i~ descrlbed ln det~ll by Wllliams and Kl~pper mentloned above. It i5 pre~erable to combine these two curves into a single function, which mey be a table of pair~ of vslues relating Ei end TDi.
Intermediate points may, of course, be found by ~nterpolstion. Once ~gain, it is important to note that -.. .... ~ - ,.. . . . ..... , ... , . .. - .... ...... . .. . .
... . . . .. ..

~ 90~8979 pcr/G~9o/ool62 `' 2~62~
the ~Ri term will normally be a small correction to Ri and thereEore A high degree o~ accuracy is no~
required to establish the relationship between Ei and TDi ' Ideally, di~ferent values ~or Ri and the relationshlp between Ei and TDi would be used for each manufacturer's paper, but in practice this would not be necessary on account o~ the nature of the small difference it would make to the performance of a replenishment system. This is further emphasized by the fact that most repleni.shment pumps are not capable of delivering liquid with a high degree of ar.curscy.
Photo~inishing printers work in one of three ways. Some expose one print at a time and immediately send each exposed print to a processing machine. Others expose small batches of prints (typically between five and thirty prints) which are sent in one long length to the processing machine. These first two types o~ printer are normally Found in minilabs where the printer is directly connected to a processor. There are still other types of printer which expose very large batches of prints, typically many hundreds, on to long rolls of pap~r ~efore being ~aken uncut to a separate processing machine. These types o~ printers are normally found in high volume photofinishing est~blishments.
If the printer is of the high volume type, the replenishment data would need to be recorded on a magnetic storage medium, such as a floppy disc. When the roll of photographic paper h~s been exposed flnd loaded lnto the paper processor, the ~loppy disc would then be loaded into the paper processor's own floppy disc drive. The p~per processor, equlpped wlth ~ microprocessor controlled replenii~hment system, would access the replenishment data via its microprocessor as the roll of photographic p~per is being proceq~ed in a developer. After a fixed number o$ prints have entered the developer, for example ten, an amount of replenisher would be added to the developer bath : , , ~, . .

WO90/08979 PCT/GB90/00162 ~ ~
10- f and an equiql amount o~ deve]oper drained off. The amount added would correspond to the sum of the replenisher amounts for the particular ten prints in the developer.
It is common practice for holes or notche~ to be punched by the prlnter on to the roll of photographic paper between prints, for use by an apparatus which chops the paper into individual prints. The paper processor could be so erranged that it counts these holes or notches so that it would know how many prints had entered it.
The replenishment information for each print may also be recorded on the print itself by means of a machine-readable code applied to the back of the print.
Alternatively, the information may be encoded as a series of punched holes between prints.
Photographic printers which only use discrete photocells for determining exposure measure only the average transmittance of a negative. A sub~ect comprising a white 5pot against a black bsckground would print as a black spot on a white background. The black spot would h~ve reached the maximum density the photogrsphic paper could give. The amount of dye in the spot would thereFore be less than that expected ~rom a calculation based on the average transmittance of the negative. Consequently, the calculated amount of replenishment required for that print would be too great.
This can be overcome by the use of a higher resolution measurement of the transmittance of the negative. A scanning device, for example a ch~rge-coupled device having a 30 by 20 ~rray, would yleld 600 measurements o the ~r~nsmit~ance of the ne~a~ive. Areas of low density on the negstive which would give ~n ~rea of Dma~ on the print could be recognised ~s ~uch, by using the paper'i RD ~ log(E) curve. The dye amounts formed ~t each of the 600 area~ could be fldded together to give ~n accurate caLculation o~ the total dye amount formed on the print.
The ultimate extension o~ this technique would be .. . . . . . . .
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~ 90/08979 PCT/GB90/00162 J~ .; ' 2~6626 to apply it to a scanning printer where the negative is scanned at very high resolution.
The present invention has the advantage that it overcomes the problem of incorrect chemical rep1enishment, thus reducing sensitometric drift, maintaining quality and therefore saving money.
The present invention would be particularly suited to a small photofini~hing operation such as a mini-lab where small chemical volumes in the processing tanks increase the susceptibility o~ the photogr~phic processor to the effects of incorrect replenishment.
~urthermore, ~or the small photofinishing operation, the relatively low hardware cost required to incorporate the present invention in a printer-processor pair is an added lS advantage. In addition, the need for a storage medium on which to retain the dye amounts calculated ~or the prints from a given roll of negatives during printing would be eliminated as the microprocessors in both the printer arlu the processor would be able to transfer the data ~etween - 20 them.
It is particularly expected that the embodiment o~ the present invention describe above wherein the replenishment rate is linked to the densiky flnd colour correction buttons would be ideally suited to a minilab where imp~ementation costs would need to be kept ~o a minimum.
~ The invention is particularly suited to the repleni~hment of photographic developers, but oould be used with any ~pparatus where the replenishment rate is a func~tion of the image density.

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Claims

1. A method of controlling the rate of replenishment of chemical solutions used in photographic processing apparatus, the apparatus including photographic printing apparatus for copying an object on to photographic material, the method being characterized by the steps of deriving a signal which is related to the exposure given to the photographic material, and using the signal to control the replenishment rate of the processing solutions.

2. A method according to claim 1, wherein the derived signal produces a replenishment rate which is directly related to the amount of image-producing substances formed on the photographic material after development of an image of the object.

3. A method according to claim 2, wherein the image-producing substances are dyes.

4. A method according to claim 2, wherein the image-producing substances are metals.

5. A method according to claim 4, wherein the metal is silver.

6. A method according to claim 1, wherein the signal is derived from measurements of the average transmittance of the object to be copied.

7. A method according to claim 1, wherein the signal is derived from measurements of the average transmittance of a plurality of different small areas of the object to be copied.

8. A method according to claim 6 or 7, wherein the signal is derived from the average of measurements of the average transmittance of a large random sample of all such objects to be copied on to the photographic material.

9. A method according to claim 8, wherein the signal is further derived from data relating to the sensitometric characteristics of the photographic material.

10. A method according to claim 2, wherein the derived signal is related to the replenishment rate by an empirical function.

11. A method according to claim 2 or 10, wherein the replenishment rate is adjusted in discrete steps which are directly related to discrete levels of density and/or colour correction used in the process of copying the object.

12. A method according to claim 11, wherein the density and/or colour correction is/are directly linked to increments or decrements in the replenishment rate applied to the developer solution in the photographic processing apparatus.

13. Photographic processing apparatus including printing apparatus for copying an object on to photographic material, and processing apparatus for processing the exposed photographic material, characterized in that a signal related to the exposure given to the photographic material is used to control replenishment rate of the solutions used in the processing apparatus.

14. Apparatus according to claim 13, wherein the signal is transmitted to the processing apparatus by a direct data link.

15. Apparatus according to claim 13, wherein the printing apparatus is provided with means for recording replenishment data on the photographic material and wherein the processing apparatus is provided with means for reading the recorded data.

16. Apparatus according to claim 13, wherein the printing apparatus and processing apparatus are provided with storage means and wherein data relating to the signal is first stored on a storage medium in the printing apparatus which is then transferred to the processing apparatus

17. Apparatus according to claim 16, wherein the storage medium is a magnetic storage medium.

18. Apparatus according to claim 13, wherein the printing apparatus has a plurality of density and colour correction buttons which are directly related to increments and decrements in the replenishment rate applied to the developer solution in the processing apparatus.

19. Apparatus according to claim 13, wherein the printing apparatus is provided with scanning means for obtaining measurements of the average transmittance of plurality of different small areas of an object to be copied.