JPS6321885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a photographic printing exposure control method in which an average value is calculated from the screen average density of a color photographic film within a certain range, and a predetermined standard value is corrected from this average value for printing. It is related to.

Most conventional color printers print using an integral neutral method. This integral neutrality method is based on Evans' principle that if you integrate the three color light components of the blue component (L _B ), green component (L _G ), and red component (L _R ) transmitted through color photographic film, the result will be approximately neutral. It is based on The density value determined from the amount of light transmitted through the film is called LATD (Large Area Average Transmission Density). LATD of three standards (standard value)
The exposure amount is determined so that the film is printed at a constant density, and the exposure amount of each film is corrected based on the difference from the standard value.

However, even when printing using this integral neutral method, the color balance is often not good. Possible causes of this include variations in the characteristic curves of color negative films, seasonal variations, and variations in color negative development processing. Therefore, it is desirable to be able to effectively correct such variations.

SUMMARY OF THE INVENTION In view of the above circumstances, it is an object of the present invention to provide a photographic printing exposure control method that corrects variations such as seasonal fluctuations and achieves good color balance.

In the present invention, the average values _B , _{G , and R} of the large-area average transmitted density of each group are calculated for each group by time or by a predetermined number _of frames.
, and only the deviation from a predetermined standard value is corrected. In other words, in the conventional integral neutral method, the standard value is always constant, and the exposure amount is determined based on this standard value so that a constant print density is achieved. This feature is characterized in that it can be corrected.

Specifically, the present invention calculates the standard exposure conditions using standard values of color photographic film, and corrects the exposure conditions based on the difference between the screen average density of the film frames to be printed and the standard values to obtain the photographic printing exposure. The control method is characterized in that an average value is calculated from the screen average density of a large number of color photographic films measured by a photoprinter every predetermined period or a predetermined number of frames, and this average value is sequentially used as the standard value. The present invention provides a photographic printing exposure control method.

The present invention will be explained below.

Figure 1 shows the average value of the large-area average transmitted density due to seasonal fluctuations, and was plotted by extracting 2,200 frames of color negative film every month and examining the average value. In this way, the hue of the subject and the color temperature of sunlight change depending on the season, and the average value changes accordingly. Therefore, if a certain standard value is determined and printed, seasonal changes in color will be ignored, resulting in poor color balance.

Therefore, if the standard value is A as shown in FIG. 2, and the average value for a certain month is B, the standard value is changed to B and exposure is performed. Specifically, the amount of deviation between the standard value A and the average value B may be determined, and the exposure conditions may be corrected by this amount of deviation.

In addition to seasonal fluctuations, variations in developing conditions,
There are variations in the characteristic curve, etc. Therefore, every certain period or every certain number of frames (for example, 1000~
10,000 frames) It is desirable to calculate the average value.

Changing the exposure conditions can be done, for example, by changing the R-
When G=0.02 and G-B=0.09 are set as standards, it can be seen that the average LATD value from August to December is lower in blue density than in May, resulting in a yellowish print. In order to make the average value of LATD from August to December the standard value, the exposure conditions are corrected so that the amount of blue exposure is reduced (minus yellow) by the deviation from the average value for May. Similarly, the exposure amount of red in January and February is corrected to be smaller.

In addition, the color has a standardization means that standardizes the shape of the characteristic curve, which differs depending on the type of color negative film, into a constant shape so that the density on the film of the same subject is the same even if the film type is different. Printer (for example, Japanese Patent Application Laid-Open No. 53-145620
No.). The average value of the screen average density of the density values obtained by standardization in the standardizing means of this printer is determined for a large number of films, and the sensitivity value or γ value is corrected by the deviation from the standard value. In other words, a standard value is determined, and the deviation between the standard value and the normalized average value is repeatedly calculated so that when a signal corresponding to the average value is input to the standardization means, a signal corresponding to the standard value is output. Fix it. These standard values are provided by the print manufacturer or determined by each photofinishing laboratory using a condition setting film.

As a means of standardization, the applicant
The circuit proposed in the patent application dated 18th (Japanese Patent Application No. 76626/1982) can be suitably used.

As described above, the present invention examines the average value of the screen average density every predetermined period or every predetermined number of frames, and corrects the exposure conditions or normalization conditions by the amount of deviation between this average value and the standard value, thereby reducing seasonal fluctuations. Alternatively, since the printing is performed taking into account variations in development conditions, it is possible to always maintain an appropriate print color balance and improve the accuracy of color correction.

[Brief explanation of the drawing]

FIG. 1 is a graph showing seasonal variations in large area average permeation concentration, and FIG. 2 is a graph showing the principle of the present invention.

Claims (1)

[Scope of Claims] 1. Photographic printing exposure control determined by determining standard exposure conditions using standard values of color photographic film and correcting the exposure conditions based on the difference between the screen average density of film frames to be printed and the standard values. The method is characterized in that the average value is calculated from the screen average density of a large number of color photographic films measured by a photoprinter at a predetermined period or every predetermined number of frames, and this average value is sequentially used as the standard value. Photographic printing exposure control method. 2. The photographic printing exposure control method according to claim 1, wherein the standard exposure condition is modified based on a deviation value between the standard value and the average value. 3. Modifying the standardization conditions of the standardization means based on the deviation value between the standard value and the average value, and determining the printing exposure amount using the density normalized by the standardization means for the photometric density of the film screen. A photographic printing exposure control method according to claim 1, characterized in that: