Method for setting conditions in photographic printing

A method for setting conditions in photographic printing exposure which is characterized in that an average density value U of a large number of negative films, a correction amount D.sub.1 of the light source and a correction amount D.sub.2 for the intended density are obtained, and when the density of the negative film to be printed is represented as U, the difference obtained by subtracting the density U from the sum of the average density value U and the correction amounts D.sub.1 and D.sub.2 is used as the printing condition for the negative film to be printed.

BACKGROUND OF THE INVENTION 
This invention relates to a method for setting conditions in photographic 
printing. 
The conditions for developing and printing of a negative film and 
development of photographic paper should be optimally controlled in order 
to produce color prints of high quality. In the majority of photographic 
printing systems currently used, a reference negative film (a negative 
film having an average density of users) is usually used as a reference to 
control the printing conditions so that printing is performed at a 
predetermined density. The reference negative film is used to optimize the 
relationship between a photographic printer and a photographic paper 
development, and is widely used as a method for correcting undesirable 
effects caused in developing and controlling a large number of negative 
films at an average density. Such control can also be achieved by using 
photometric values of a negative film in printing. However, this method 
involves troublesome work in preparing reference films. Furthermore, since 
reference films are usually supplied to a development laboratory in the 
state already developed under standardized conditions, particular negative 
characteristics or the minute differences unique to a particular 
laboratory are not taken into account in preparation. Moreover, since such 
reference negative films do not include differences in region, climate and 
season nor consider color fading or quality fluctuations of the reference 
films per se, they are not able to indicate optimal printing conditions 
for development laboratories. As long as a reference negative film is 
used, all of the work for setting and controlling printing conditions have 
to be done manually. Since the manual work is often conducted without much 
care, films are printed frequently under inappropriate printing 
conditions. 
SUMMARY OF THE INVENTION 
An object of this invention is to provide a method for automatically 
setting conditions for a photographic printer and constantly controlling 
the conditions at predetermined values. 
Another object of this invention is to provide a method for setting 
conditions in printing which gives considerations to difference in 
development process, region, climate and season by obtaining the 
conditions from an average value of users. 
Still another object of this invention is to provide a method for setting 
conditions for photographic printing which comprises feeding light in an 
amount equivalent to the users' average value to a photographic paper, 
controlling the conditions so as to keep density deviations within a 
predetermined scope and preventing color fading or fluctuations, so as to 
thereby eliminate the troublesome work of setting printing conditions 
every time, and constantly print a large number of negative films under 
predetermined conditions. 
According to this invention, in one aspect thereof, for achieving objects 
described above, there is provided a method for setting conditions in 
photographic printing exposure which is characterized in that an average 
density value U of a large number of negative films, a correction amount 
D.sub.1 of the light source and a correction amount D.sub.2 for the 
intended density are obtained, and when the density of the negative film 
to be printed is represented as U, the difference obtained by subtracting 
said density U from the sum of said average density value U and the 
correction amounts D.sub.1 and D.sub.2 are used as the printing conditions 
for the negative film to be printed. 
According to this invention, in another aspect thereof, for achieving 
objects described above, there is provided a method for setting conditions 
in photographic printing exposure which is characterized in that an 
average density value U of a large number of negative films, a correction 
amount D.sub.1 of the light source and a correction amount D.sub.2 for the 
intended density are obtained, filters are controlled under respective 
conditions, the density of printed photographic paper is measured without 
using a negative film, and said correction amount D.sub.2 is modified 
based upon the difference between the measured density and the intended 
density. 
According to this invention, in still another aspect thereof, for achieving 
objects described above, there is provided a method for setting conditions 
in photographic exposure which is characterized in that an average density 
value U of a large number of negative films, a correction amount D.sub.1 
of light source and a correction amount D.sub.2 for intended density are 
obtained for three primary colors respectively, and when the density of 
the negative film to be printed is represented as U, said negative film is 
printed with the amount calculated by subtracting said density U from the 
sum of said average density value U and the correction amounts D.sub.1 and 
D.sub.2, the density of printed photographic paper is measured for each of 
the three primary colors, and said correction amount D.sub.2 is modified 
based on the difference between the measured densities and said intended 
densities. 
The nature, principle and utility of the invention will become more 
apparent from the following detailed description when read in conjunction 
with the accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION 
FIG. 1 shows an embodiment of a photographic printer including color 
compensation filters and cut filters to which this invention method is 
applied. In the figure, a negative film 1 is illuminated with the light 
from a light source 4 via color compensation filters of yellow (Y), 
magenta (M) and cyan (C) and a mirror box 3, and the light transmitted 
through the negative film 1 passes through cut filters 5 of Y, M and C, a 
lens unit 6 and a black shutter 7 to expose photographic paper 8. The 
photographic paper 8 is wound on a supply reel 81. The photographic paper 
8 which has been exposed at the printing section having an optical axis LA 
is processed at a processing section 10 for development, bleaching, 
fixing, washing and drying, and is reeled on a take-up reel 82. 
Photosensors 9 such as photodiodes are provided near the negative film 1 
on the side of the lens unit 6 to detect the image density in three 
primary colors blue (B), green (G) and red (R). Detection signals for each 
of BGR from the photosensors 9 are amplified by amplifiers 11, converted 
into density signals DS by logarithmic converters 12 and inputted into a 
control circuit 13 which determines printing conditions together with an 
exposure determining circuit 14. The color compensation filters 2 are 
controlled by a color compensation filter driving circuit 15, the cut 
filters 5 are controlled by a cut filter driving circuit 16, and the black 
shutter 7 is controlled by a shutter driving circuit 17 to print the 
negative film 1 which has been conveyed to the printing section. The color 
compensation filters 2 which are used for color compensation herein may 
have a structure as shown in FIGS. 2A and 2B. Three filter plates 21 (21A 
through 21C) of a sectoral quadrant shape are combined for each of the 
three colors of yellow (Y), magenta (M) and cyan (C). A pair of filter 
plates 21A to 21C or a left and a right filter plates are relatively moved 
in horizontal direction to adjust the amount of light transmitted through 
a central light path 22 for each color. The movement of the filter plates 
21A through 21C is controlled for each color by the driving circuit 15. 
Respective filter plates 21A through 21C are approximated to the spectral 
transmittance distribution of the negative film dyes so as to print images 
of excellent quality. According to this invention, the actual printing 
density of a printed photographic paper 8A is measured at a stage 
subsequent to the printing at the processing section 10. The processed 
photographic paper 8A is illuminated by a light source 31 and the light 
reflected therefrom is detected for each of BGR by photosensors 33 such as 
photodiodes via a color separation filter 32, amplified by amplifiers 34 
and converted into density values RD by logarithmic converters 35. The 
density values RD are inputted into an computing unit 30 which examines 
the relationship between the printing density and the exposure, and 
corrects them with an amount of correction which has been determined by 
the exposure determining circuit 14 when predetermined conditions are met. 
Operation will now be described in more detail referring to the flow chart 
of FIG. 3. 
According to this invention, a large number of negative films (e.g., 1,000 
pieces) are photographically measured (Step S3) by photosensors 9 at each 
laboratory to obtain an average density U.sub.i (i=B, G, R) for each of B, 
G and R (Steps S1 and S2). The average density value U.sub.i is equivalent 
to the density of a conventional reference negative film, and it is 
obtained by incorporating the particular characteristics and conditions in 
processing of a photographic printer used in photometry, climatic and 
seasonal differences and the like. The average density value U.sub.i of 
negative films may be obtained from the national average value or the 
average value of several photographic printers instead of the particular 
printer used. With reference to thus obtained average density value 
U.sub.i, the density of 0.5 or less is termed as "under-negative" (j=1), 
that of 1.0 or more as "over-negative" (j=2) and that therebetween as 
"normal negative" (j=3). The average of these three classes is the average 
density value U.sub.ij. In the photographic printer of the type as shown 
in FIG. 1 where color compensation filters 2 comprise the three colors of 
Y, M and C, the exposure time for each color can be made constant if the 
amount of light for three colors is adjusted by varying the area inserted 
in a light path 22 or varying transmission factors. In this case, the 
system does not require the cut filters 5 and the cut filter driving 
circuit 16. The exposure time may be changed depending on the density of 
negative film 1. In this case, the exposure time must be controlled by cut 
filters 5 for each color. Color compensation filters 2 and cut filters 5 
may also be combined in a printer system. It is desirable to make the 
spectral sensitivity characteristics of the photosensors 9 coincide with 
or approximate to the spectral sensitivity characteristics of photographic 
paper 8. If the sensitivity characteristics are not aligned, it is 
recommended that a correction value be obtained by using spectral 
sensitivity distributions of the photosensors 9 and the photographic paper 
8 in advance so as to be able to correct the value constantly. 
The density of a negative film 1 may be obtained from the amount of light 
measured by the photosensors 9 at a predetermined filter position. 
Therefore, the amount to be corrected is obtained by determining the 
filter position where the amount of light received is constant in absence 
of the negative film 1, then amplifying the value of light amount of the 
photosensors 9 by amplifiers 11 and then logarithmically converting the 
value into the value D.sub.1 by logarithmic converters 12 (Step S11). If 
the color compensation filters 2 are controlled to (D.sub.1 +U.sub.ij) by 
the control circuit 13 and the color compensation filter driving circuit 
15 to achieve the average density value U.sub.ij, the light in an amount 
equivalent to the reference negative film can be given to the photographic 
paper 8 without using a reference negative film. In order to expose the 
photographic paper 8 at the intended density in BGR, the filter plates 21A 
through 21C of the color compensation filters 2 are controlled (D.sub.2) 
by the control circuit 13 and the driving circuit 15 (Step S12). The 
standard printing conditions (D.sub.1 +D.sub.2 +U.sub.ij) can be obtained 
to give a predetermined amount of light onto the photographic paper 8 just 
as a reference negative film is used. The value is stored in memory (Step 
S10). The above mentioned steps S1 and S2 and steps S10 through S12 are 
executed in the control circuit 13 and the exposure determining circuit 
14. If the density of a negative film which is to be printed is similarly 
measured by the photosensors 9 and the value is represented as U and the 
control of the color compensation filters 2 as D.sub.3, the following 
relationship holds: 
EQU U+D.sub.3 =D.sub.1 +D.sub.2 +U.sub.ij (1) 
Therefore, the unknown control amount D.sub.3 can be calculated from the 
formula below (Step S4): 
EQU D.sub.3 =D.sub.1 +D.sub.2 +U.sub.ij -U (2) 
Exposing is conducted by controlling the color compensation filters 2 
(and/or the cut filters 5) (Step S6), and the exposed paper is processed 
for development, etc. at the processing section 10 (Step S7) and wound on 
a take-up reel 82 (Step S8). The photographic paper may be cut in a 
predetermined length instead of being wound on the take-up reel 82. 
Alternatively, the color compensation filters 2 may be driven until the 
time that they becomes equal to (D.sub.1 +D.sub.2 +U.sub.ij) when the 
negative film 1 is U. As it takes much time to repeatedly control the 
color compensation filters 2 for measurement and focusing, the operation 
may be combined with the one represented by the formula (2). 
For setting printing conditions by the control circuit 13 and the exposure 
determining circuit 14 in a printer, it is necessary to obtain in advance 
the correction amount D.sub.1 and the control amount D.sub.2 so as to make 
the amount of light constant. The correction amount D.sub.1 for light 
source variation may be included within the control amount D.sub.2. In 
this case, the correction amount D.sub.1 should be calculated every time 
the light source is changed (for instance, daily). The printing conditions 
may be controlled either by adjusting the value D.sub.2 in a manner that 
the predetermined printing density of the photographic paper 8A is 
maintained at a constant value or by controlling the value D.sub.2 in a 
manner that the amount of light under the standard printing conditions 
(D.sub.1 +D.sub.2 +U.sub.ij) is kept at a constant value. The latter is 
simple. The printing conditions may be set or controlled thereafter in 
different methods. Alternatively, the values D.sub.1, D.sub.2, U.sub.ij or 
U may be measured or controlled either in combination or separately. The 
average density value U.sub.ij may be the average value of the densities 
observed up to the day before or the average of the densities of a given 
period of time. Furthermore, the average density value U.sub.ij may be 
prepared by processing plural raw data with smoothing or interpolating. 
It is possible to monitor the negative film development processing simply 
by monitoring the average density value U.sub.ij. As the printing with the 
color compensation filters 2 alone corresponds to a negative film without 
contrast, and there may be a slight difference in characteristic outputs 
particularly in the non-linear section, it is desirable to seek the 
relationship between the average density and the average density of 
essential sections from a large number of negative films photographed by 
users in advance so as to be able to correct the above mentioned method. 
The correction value may take the gradation of each photographic paper 
into account. 
According to this invention, the above correction amount D.sub.2 is 
corrected based upon the degree of difference between the intended density 
and the measured density value of a particular photographic paper 8A which 
has been actually printed in order to perform optimal control over the 
printing operation. More specifically, color compensation filters 2 
(and/or cut filters 5) are driven under the printing conditions set at the 
above mentioned Step S10 (Step S20), and the photographic paper 8 is 
exposed at the printing section (Step S21) and processed for development, 
etc. at the processing section 10 (Step S22). Frames of the paper 8A on 
which images have been printed are detected (Step S23) by simply detecting 
the passage of the photographic paper 8, by detecting the passage of a 
predetermined duration of time from the printing operation (e.g. 10 
minutes), or by detecting that a predetermined length of paper has been 
transferred from the printing section (e.g. 2 m). The position for this 
detection is aligned with the position of the light source 31 in FIG. 1. 
The light from the light source 31 is reflected from the printed 
photographic paper 8A to be inputted in the photosensors 33 via a color 
separation filter 32 and the detection signals for BGR are respectively 
amplified by the amplifiers 34 to be inputted into logarithmic converters 
35. In this manner, the printing density values RD of the paper 8A which 
has been printed can be respectively obtained for three colors (Step S24). 
This photographic measurement may be conducted after the paper is cut. 
Thus obtained printing density value RD is compared with the intended 
density by the computing unit 30 and whether or not the difference 
therebetween remains within a permissible range (Steps S25 and S26) is 
judged. If the difference remains in the permissible scope, then the 
process proceeds to the above mentioned step S3 for repeatedly conducting 
printing and processing (Steps S3 through S8). The permissible difference 
is, for instance, .+-.0.03. If the difference is outside the range, on the 
other hand, a correction amount .DELTA.E required for the particular 
difference is calculated (Step S27) and the printing condition D.sub.2 
which has been stored at Step S10 is corrected to (D.sub.2 +.DELTA.E). An 
alarm may be outputted by means of a lamp and so on. The above formula (1) 
becomes 
EQU U+D.sub.3 =D.sub.1 +(D.sub.2 +.DELTA.E)+U.sub.ij (3) 
The control amount D.sub.3 will be 
EQU D.sub.3 =D.sub.1 +D.sub.2 +.DELTA.E+U.sub.ij -U (4) 
With the above formulae, the exposure amount determined at the above step 
S4 is corrected to modify subsequent printing process. In this manner, the 
density of printing is constantly adjusted to be the intended value. The 
steps S10 through S12 and S20 through S27 in FIG. 3 show the procedure of 
setting and controlling of printing conditions while the steps S1 through 
S8 and S10 the procedure of printing of users' negative films. As 
mentioned above, this invention enables to achieve fully automated process 
for setting and controlling conditions as it completely eliminates the 
variable factors which conventionally affect the amount of the light in 
printing such as fluctuations in negative film development process, 
printers and paper development process, without using the measurement of 
users' negative film density and negative films. This invention comprises 
steps of irradiating photographic paper with the light in an amount 
equivalent to the users' average negative film, correcting the light 
source for printing, monitoring the modification of the process after the 
development of paper and correcting the exposure conditions. 
Although the values D.sub.1, D.sub.2, D.sub.3, U.sub.ij and U are described 
as density values in the foregoing statement, it is possible to calculate 
and control them in terms of the amount of transmitted light or the filter 
position. 
Printing conditions may be set in a manner similar to the above even in the 
photographic printer of a three color luminance-change type with three 
light sources of RGB which is adapted to print by varying the luminance of 
three colors so far as the negative films can be precisely measured and 
exposure on the photographic paper is accurately controlled. It is 
desirable in this case that the filters of RGB used as light sources are 
bandpass filters. If conditions require broad filters as the amount of 
light is not sufficient, it is necessary to determine correction value by 
using the spectral sensitivity of the paper at a given amount of light and 
the spectral sensitivity of the photosensors in advance. If this invention 
method is applied to photographic printers of a white-light subtractive 
type wherein the amount of RGB light is controlled timewise by cut 
filters, it is necessary to obtain the amount of RGB light illuminated 
onto the photographic paper taking into account irregular absorption by 
the cut filters as well as reciprocity law failure. This involves 
complicated operations. In the case where the photosensor can measure the 
light through cut filters of YMC, it is possible to set conditions in the 
manner similar to the above. Although the density of the printed paper is 
measured with reflected light in the above description, it may be measured 
with transmitted light. 
As this invention method obtains and sets the printing conditions from the 
users' average value, it is possible to include the difference in 
development fluctuations, climate, season in a set value. Since this 
invention method feeds the light in an amount equivalent to the users' 
average value to the photographic paper without using negative films to 
keep the density at a given balance, it can be controlled to eliminate 
density variations or color fading. This invention method also eliminates 
complicated operation in setting conditions for each time to thereby 
facilitate photographic printing of a large number of negative films 
constantly under a predetermined conditions. 
Since it is not necessary to prepare nor use reference negative films, the 
photographic printing operation can be performed at a higher efficiency. 
As this invention method enables automatic setting of printing conditions 
as well as automatic control thereof, the steps which conventionally 
required skilled manual labor can be automated fully to enhance the 
efficiency to a remarkable degree. 
It should be understood that many modifications and adaptations of the 
invention will become apparent to those skilled in the art and it is 
intended to encompass such obvious modifications and changes in the scope 
of the claims appended hereto.