JPH0640192B2 - Normalization method of photometric value in photo printing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for normalizing photometric value data of three primary colors in a color photographic printing apparatus.

(Technical background of the invention and its problems) When a gray image of an original film to be printed in three primary colors of RGB is measured by a color photographic printing apparatus, the RGB photometric values are the same as shown in FIG. It is neither the same as the exposure dose nor parallel to the exposure dose. This depends on the development process and the type of the photosensitive material. This is because it is only necessary to obtain an appropriate reproduced image by combining a negative film, which is the original film used for printing, with a photographic printing paper, which is the material to be printed, and the usage of the material differs depending on the type of material used. This is due to the fact that the manufacturing companies have different design concepts, and that they are also related to variations in development processing characteristics and the photometric filter characteristics of the original film. In this way, when the photometric values of the three primary colors do not have the same characteristics, the film densities and colors differ even for the same subject. For example, even a blue sky may have a density similar to gray cloudy sky, which causes a great inconvenience in color correction and determination of the exposure amount. In this way, depending on the type of sensitive material and the development process
The RGB sensitivity and gradation balance are different, and the determination in the density and color of the negative film and the control will be incorrect. It is necessary that the same subject has a constant density and color on the negative film regardless of the photosensitive material type and the developing process. For this reason, conventionally, the RGB photometric values are normalized as shown in FIG. 5, but there are drawbacks as described below.

For example, Japanese Unexamined Patent Publication No. 53-145620 discloses a hue extraction having a means for correcting sensitivity by adding a constant to blue, green and red density signals and a normalizing means for amplifying the density signal and performing γ correction. A device is disclosed. However, there is no description about the method for obtaining the sensitivity correction amount and the γ correction amount, and in practice, it is necessary to create standard negatives for various sensitive materials at appropriate intervals and obtain the correction amount using this standard negative. .
There is a drawback in that it is troublesome to determine the amount of correction and the amount of correction including what is used as the standard negative.
The photographic printing conditions are conditions determined based on the film sensitivity and the γ value, and have the same purpose as the film normalization. However, conventional printing conditions include characteristics of photographic printing papers and printers, so that it is difficult to determine the γ value of the film from the slope control value related to the γ value of the film. Further, it has been very troublesome to determine and manage the printing conditions in the past. Therefore, it is insufficient for the above-mentioned purpose.

Further, JP-A-56-30121 shows a method of successively correcting the deviation between the average value and the standard value of a large number of frames of the large area average transmission density (LATD). However, this method corrects the correction coefficient of the photometric value using the normalized average value of the densities, and does not obtain the correction coefficient of the photometric value.
In this method, since the correction is performed sequentially, the normalization condition is corrected very slowly, and there is a possibility that it will not converge. Further, no correction to the gradation is shown.

Further, Japanese Examined Patent Publication No. 50-10730 shows that a constant proportional to the average density of the reference negative film and the reciprocal of the gradation is used as a judgment formula for detecting the subject color ferria. However, this method is for investigating that there is no difference in RGB density between the reference negative and the printing negative, and is also inconvenient in that the reference negative must be used.

As described above, there has been a demand for a method of automatically determining the film characteristics (that is, density and gradation balance, etc.) that differ depending on the film type and the developing process, and controlling the exposure, but it has not been realized yet.

(Object of the Invention) The present invention has been made under the circumstances described above.
An object of the present invention is to provide a method capable of correctly and accurately normalizing RGB photometric values in a color photographic printing apparatus, and further, the printing apparatus automatically follows changes in the developing process. The object of the present invention is to provide a method of normalizing photometric values in a photographic printing apparatus, which counts as an operator when the quality cannot be guaranteed, always maintains high quality by exchanging a developing solution, and can be used by an inexperienced person.

(Summary of the Invention) According to the present invention, an exposure control characteristic value is obtained according to an original film type and a development process, an exposure amount is calculated from the exposure control characteristic value, and a printing condition is automatically determined. In the photo printing apparatus, the screen characteristic value density is determined for a plurality of original image films in advance by photometry of the three primary colors for each film / frame of the original film, and the screen characteristic value density is compared with preset density division values. The density of the screen characteristic values and the average value of the screen characteristic value densities for each classification group and stored in a predetermined memory; The method further comprises a step of calculating a correction coefficient of the primary color photometric value, and a step of normalizing the three primary color photometric values of the original image film by the correction coefficient when a new original image film is printed to generate a characteristic value for exposure control. Photo The present invention relates to a method for normalizing a photometric value in a printing apparatus.

(Embodiment of the Invention) FIG. 1 is a block diagram of an apparatus for realizing the method of the present invention, in which a color negative film as an original image film to be printed by a photodiode, an image sensor or the like is measured with three RGB primary colors. (1), the exposure control characteristic value (for example, average density, maximum density, minimum density, etc.) 6 is obtained from the density value obtained from the photometric data, and this characteristic value 6
Is used to calculate the exposure amount 7 according to a predetermined calculation formula, whereby the exposure control 8 of the photographic printing apparatus is performed. At the same time, the characteristic value of the screen (for example, the average density, the maximum density, the minimum density, the density histogram, the tint, etc.) of the screen 2 is obtained from the photometric data of the photometric 1, and the screen characteristic value 2 is stored in the memory 5. To do so. Then, the correction coefficient and the constant 4 are obtained from the data stored in the memory 5, and the correction 3 of the density value obtained from the photometry 1 is performed, and the exposure control characteristic value 6 is obtained according to the correction result. .

Here, when the density division value is 1, the screen characteristic value density average value is calculated and stored separately for two large and small classification groups, and the characteristic value 2 obtained from the photometric value by photometry 1 and the predetermined density division The values are compared, and the average value of a large number of frames having a characteristic value larger than the density division value is stored as A _j , and the average data of a large number of frames having a characteristic value smaller than the density division value is stored as B _j . j = 1, 2, 3 or R, G, B, and the correction coefficient 4 for normalizing the photometric data is obtained by A _j , B _j and the combination thereof. For example, let the photometric value be D _ij and the correction value be D ′.
_In the case of _ij , the gradation correction coefficient and the density balance correction coefficient are obtained by the combination of A _j and B _j . For example, when normalization is performed with G of the three-color photometric data as a reference, When normalizing the RGB photometric data with reference to a predetermined film characteristic curve, It can be calculated as In the above equation (1), K = B ₂ may be used, or B ₁ or A ₁₃ may be used as a reference. Further, S _j and G _j in the above equation (2) are reference values. After normalizing the slope with respect to D _ij in _Eqs. (1) and (2), B ₁ , B ₂ , B
You may make the correction by ₃ . Further, instead of D _i1 , D _i2 , and D _i3, a color difference value composed of a combination of those two colors or three colors can be obtained. As described above, the normalization method of the present invention is not limited to the equations (1) and (2). For example, a method of using a constant value given in advance as the gradation correction value in the equation (1) is also possible.

FIGS. 2 (A) to 2 (C) show how G and R are normalized by the equation (1) above with reference to G in the photometric data.
If the actual measured values are shown in FIG. 7A, first, the gain is corrected so that B ₁ = B ₂ by R ′ = RB ₁ and G ′ = GB ₂ (see the drawing (B )), And then γ-correction, R ″ ＝ (RB ₁ ) ・ {(A ₂ -B ₂ ) / (A ₁ -B ₁ )} + B ₂ , G ″
= G makes it more accurate and becomes as shown in Fig. 6 (C). By converting the density value using the normalization condition obtained for each film type, the same subject has the same density or the same color. As a result, the exposure amount calculation can be obtained under the same condition even if there is a film type or process variation. Therefore, only one type of exposure calculation software is required.

The exposure control characteristic value 6 is obtained by correcting the density value 3 obtained from the photometric data with the correction coefficient 4 obtained as described above. In this case, when the double-sided average density is used as the screen characteristic value and it is set as DL _j , Can be found at. In determining the printing conditions, when the film characteristic setting unit is separated and independent from the conventional method, the exposure can be controlled using the normalized density value in the present invention, and the printing conditions are automatically determined and managed. It becomes possible to do.

FIG. 3 shows another example of the present invention. The screen characteristic value is obtained after normalization 11 of the density value obtained from the photometry 10 is performed.
12 is obtained, the exposure amount 13 is determined according to the screen characteristic value 12, and the exposure control 14 is performed. put it here,
For normalization, the screen characteristic value 12 is used to perform conversion 15 to the screen characteristic value before normalization, the converted data is stored in the memory 16 to obtain the normalization coefficient / constant 17, and photometry is performed according to these values.
Normalized the 10 density values as described above, and converted data
I am trying to fix 15. In this case, in particular, the photometric value can be logarithmically converted to a density value and the density value can be normalized 11 at the same time.

(Modification of the Invention) The density division value described above may be two or more, and in the case of two,
Three average values of the characteristic values are obtained, and two sets of correction coefficients for the low density portion and the high density portion are obtained. Further, as shown in FIG. 6, divided values X _{1 to} X ₄ can be set, and overlapping concentration ranges can be set such as X ₂ or less, X ₁ to X ₄ , X ₃ or more. By defining a large number of density division values, the shape of the film characteristic curve can also be estimated. From the estimated shape of the characteristic curve of the film, the overexposure and the underexposure part can be properly exposed and controlled. The density division value may be a constant value given in advance, or may be the average value of the characteristic values obtained from the photometric data, and is set so that the number of data classified into larger and smaller than the division value is similar. It is good to be done. Furthermore, it is better to select and correct the data, for example, to remove abnormal values (low density, high density, data whose color balance is significantly out of range, etc.) or to set a possible limit. It is possible to converge to the accurate average value obtained by. Set the upper and lower limits for the number of accumulated data (number of frames), and when the upper limit is reached, restart the data averaging process from the beginning. On the other hand, until the lower limit is reached, the correction value is not used and the initial setting is performed. A value may be used, or an average value of all negatives including each negative type may be used as a correction value. The correction value may be obtained for each sensitive material type (common to various types or several types), and the data averaging process may be performed for each frame, for each order, for each order, by accumulating necessary data. Alternatively, the added value of the characteristic values may be stored instead of the average value, and the averaging process may be performed at the top of one order, when the printer channel is switched, or the like.

Although the normalization of the photometric value or the density value has been described above, the screen characteristic value or the exposure control characteristic value may of course be normalized. Further, the normalization condition can be used by converting the coordinate point of the characteristic value shown on the color coordinates into the rotation amount of the coordinate axis or the moving amount of the coordinate table. Since these methods do not convert individual photometric points, they are superior in processing speed.

The characteristic values used to calculate the average value are the average density of all or part of the screen, the weighted average value, the average density value of the selected points, the intermediate value between the maximum density and the minimum density, the average of the main part or the background part. It is possible to use the density value, etc., and to display the abnormalities and fluctuations of the development process and the photometric device by means of the average value or the normalization coefficient, and to output an alarm. It suffices to automatically correct the conditions. Furthermore, the difference in the printing conditions between the sensitive materials may be detected by utilizing the difference in the average value between the sensitive material types, and the automatic correction or the exposure control amount may be changed. Although the original film used in the present invention has been described with the negative film, it can be applied when other reversal film or printed photographic paper is used as the original image for printing, and further other copying materials (heat, magnetism, etc.) and images can be used. It can also be applied to display devices and the like.

(Effects of the Invention) As described above, according to the present invention, the standard negative is unnecessary,
Normalization can be set automatically for each film as the original film to be printed, and changes in the development process, film milk number, season, and photometric device can be automatically corrected, resulting in highly accurate exposure. Control becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram for realizing the method of the present invention, and FIG.
(A) ~ (C) is a diagram for explaining the normalization of the present invention, the third
FIG. 4 is a block diagram showing another example of the present invention, FIGS. 4 and 5 are diagrams for explaining conventional normalization, and FIG. 6 is a diagram for explaining how to determine density division values. 1, 10 ... Photometry, 2, 12 ... Screen characteristic value, 3, 11 ... Density value correction, 4 ... Correction coefficient, constant, 5, 16 ... Memory, 6 ... Exposure control characteristic value, 7 ... Exposure amount calculation, 8 ... Exposure control.

Claims (3)

[Claims] 1. A photographic printing apparatus in which an exposure control characteristic value is determined in accordance with an original film type and a development process, an exposure amount is calculated from the exposure control characteristic value, and a printing condition is automatically determined. , For a plurality of original image films, the screen characteristic value density is obtained by photometrically measuring the three primary colors for each film / frame of the original film, and the screen characteristic value density is compared with a preset density division value to determine the size of the density. And classifying each of the classification groups to obtain an average value of the screen characteristic value densities and storing the average value in the predetermined memory; The method further comprises a step of calculating a correction coefficient, and a step of normalizing the photometric values of the three primary colors of the original image film by the correction coefficient when a new original image film is printed, and generating a characteristic value for exposure control. Copy Normalization method of photometric value in printing apparatus. 2. A method for normalizing a photometric value in a photographic printing apparatus according to claim 1, wherein the photometric value is pixel data. 3. A method for normalizing a photometric value in a photographic printing apparatus according to claim 1, wherein the correction coefficient is a gain or a γ value.