JP2520020B2 - Exposure amount determination method for image copying apparatus - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of determining an exposure amount of an image copying apparatus, and more particularly to an automatic photo printing apparatus (automatic printer for printing an image from a color photograph such as a color film onto a color paper). ) The method for determining the exposure amount for photographic printing for determining the exposure amount.

[Problems to be Solved by Prior Art and Invention]

The color negative is B (blue), G (green), R for the entire screen.
It is known empirically that the (red) three-color light is transmitted, but the transmission ratios of these three color components are generally substantially equal or constant. Therefore, in the automatic printer, the printing light amount (exposure amount) is determined based on the following formula.

logFj = Kj + Dj (1) where logF is the logarithm of the amount of printing light, K is a constant, D is the integrated negative transmission density (LATD) measured by the photometric system, and j is B,
The color light is either C or R.

However, if the amount of printing light is controlled by the automatic printer based on the above formula (1), the print from the under-exposed negative has a higher overall density than the print from the proper negative, and the print from the over-exposed negative has a higher density. Will be lower. For this reason, a slope control circuit is provided to
The exposure amount is determined by correcting Dj. on the other hand,
Even in automatic printers equipped with a slope control circuit as described above, negatives that have changed significantly over time, negatives (different types of light source negatives) taken with light sources (fluorescent lamps, tungsten lamps, etc.) that are significantly different from daylight, and color areas With a negative or the like having a defect, defective print with an incorrect color balance is likely to occur. Further, film manufacturers (films of different types) having different sensitivities (different film types) have different sensitivities, densities, etc. of the three photosensitive layers, so that good prints cannot be produced under the same printing conditions. For this reason, Dj in the equation (1) is corrected (color correction), and the exposure amount is determined by changing the slope control circuit value in a different type film. At this time, overcorrection is referred to as high correction, and undercorrection is referred to as lowward correction. The accuracy of B deteriorates.

However, in recent years, high-sensitivity films, films with different applications, new films with various improvements, and the like have been released from each manufacturer every year, and the number of films has become very large, and now there are dozens of films. However, since the printing exposure conditions for each film type do not necessarily match, it is necessary to determine the printing exposure conditions for each film type. Takes time. For this reason, the following technique has been proposed in which an appropriate printing exposure condition for each film type is automatically determined from one standard printing exposure condition.

Japanese Examined Patent Publication No. 56-15492 compares the ratio of the color densities of the photometric values of each image point B / G, G / R, R / B to a fixed value, and one of the three primary colors is It is disclosed that a large photometric value is not used for determining the exposure amount, by examining whether or not it is large with respect to the primary colors. Further, JP-A-51-94927 discloses that
There is disclosed a technique of determining an exposure amount by a photometric value obtained by removing a photometric value deviated by a certain amount from a reference value of a standard image of each film type. Since these techniques need to give a comparison value or reference value specific to the film type, it is necessary to input data indicating the film type and to create and store the comparison value or reference value for each film type. There is a drawback.

In order to solve this drawback, Japanese Patent Application No. 63-245810 discloses that a large number of image densities are stored for each film type in correspondence with the code indicating the film type stored in the film, and the stored data The reference value for each is obtained, the code is read to determine the film type of the film to be printed, and the film is selected from the reference values and printed from the photometric value of the film to be printed and the standard printing exposure conditions. It is disclosed to determine the exposure dose of the film to be exposed. According to this method, the reference value can be automatically obtained, but it cannot be applied to a film type that does not have information such as a code indicating the film type (for example, 110 film, brownie film, disc film, etc.). There are drawbacks.

As a method to determine the exposure amount for printing without using the information on the film type, a method for selecting the exposure value by selecting the exposure value using a curve showing the color balance characteristics obtained from the exposure value each time the original copy in the film is copied. Is known (Japanese Patent Application No. 55-46741). However, the color balance characteristic curve is obtained from the test-exposed portion burned into the film, which is quite difficult in practice.

The technique disclosed in Japanese Patent Laid-Open No. 54-110829 obtains the exposure amount from a large number of photometric values of one film image, and it is necessary to finish the photometric measurement of one film before printing. is there. Therefore, as in the technique described in JP-A-59-220761, the photometric unit and the exposure unit are separated from each other, or in the same place as in the technique described in JP-A-61-91648. In an apparatus having a printing section and a printing section, it is necessary to carry the film once conveyed for photometry and printing in the opposite direction, and it is difficult to increase the speed. Further, there is a drawback that the film is easily scratched because the number of times the film is conveyed increases.

Further, in JP-A-59-220760, the lowest density point including the mask density in the original image of the film strip or its periphery is obtained, and the neutral density of the measurement point with respect to the lowest density point is increased. The limit value of the chromaticity at the measurement point is enlarged, and the value for the lowest density of each measurement value obtained by scanning the copy original image for the three primary colors is compared with the limit value, and photometry not exceeding the limit value. Selecting points is disclosed. This technique relies on the fact that the measurement point with the lowest density of the film strip including the negative and its periphery or the original image is close to the mask density, and therefore the chromaticity of each image is not large.

However, this method has the following drawbacks. That is, the film characteristics (three-color sensitivity balance, three-color gradation balance, linearity of characteristic curve, etc.) cannot be known from the mask density. Therefore, although a method for obtaining the limit of the measurement point with respect to the lowest density point is set in advance, it is insufficient for the influence of the film type, the negative developing performance variation, the difference in the photometric device, and the like. Therefore, the color balance characteristic curve described above is calculated for the value (photometric value) of the selected photometric point. However, for this reason, the drawbacks described in JP-A No. 54-110829 are still unsolved.

The present invention has been made to solve the above problems, and high-speed printing processing is possible without the need for information indicating the film type when printing various films under the standard film type printing exposure conditions. It is an object of the present invention to provide a method for determining an exposure amount of a simple image copying apparatus.

[Means for solving the problem]

In order to achieve the above-mentioned object, the present invention obtains three-color photometric data by dividing a color film on which an image is recorded into a large number of pieces to perform photometry, and measures the low-density area in the color film including the image recording section. The three-color corrected photometric data is obtained by correcting the three-color corrected photometric data by data, and the three-color standardized data is obtained by converting the three-color corrected photometric data according to a predetermined conversion condition and normalizing the data. , Comparing the three-color standardized data with a reference value to classify the three-color standardized data, select the three-color photometric data according to the classification of the three-color standardized data, and select the selected three-color photometric data. The exposure amount is determined based on the average value.

Further, it is possible to classify the three-color standardized data by deciding which one of the areas divided into a plurality of predetermined two-dimensional or three-dimensional coordinates the three-color standardized data belongs to.

The low-density area photometric data is the minimum density data in the image recording area of the color film, the minimum density data other than the image recording area of the color film, and the minimum density data of the area across the adjacent images recorded in the color film. be able to.

[Action]

Hereinafter, the operation of the present invention will be described. FIG. 2 shows A, B, C,
The standard photographic subject is photographed by sequentially changing the exposure amount using a D4 type negative film, and the average density obtained by photometrically measuring those film images is shown by the horizontal axis being RG and the vertical axis being GB. It is shown on the color coordinates. FIG. 3 shows the image densities obtained by subtracting the film mask densities from the respective average densities of FIG. 2 on the color coordinates. As can be seen from FIG. 3, the densities of the image parts of the respective films obtained by subtracting the mask densities from the average densities are substantially similar except for the high densities of the film C.
FIG. 4 shows a large number of images (about
The average density of 100 frames) is divided into four density levels and shown on the color coordinates. The upper end of the broken line shows the mask density. Three of the four films are very different. FIG. 5 shows the densities obtained by subtracting the mask densities from the respective average densities and the average values of the densities of the four films on the color coordinates. Similar to FIG. 3, the densities of the film image areas are substantially similar. There is.

However, there has been no such agreement in negative films until recent years. In most cases, it is used in combination with a negative film and paper produced by only one or a very small number of manufacturers, and it suffices if a good photographic print can be obtained with that combination. Other combinations were not fully considered. However, as a result of the widespread use of various films worldwide in recent years, there have been enormous cases of combinations of various negative films and various color papers. In order to be able to use any combination, it is necessary that the characteristics of the gradation balance of each film are similar. The results of FIGS. 2 and 4 show that the gradation balance characteristics of various films are similar.

However, since the characteristics of the coloring material used in each film are not the same and the technology for designing the photosensitive material is not the same, the mask density does not match each film type.

6 and 7 show the values obtained by subtracting the photometric data of the low density area of the image portion of the film from the average density instead of the mask density on the same color coordinates as in FIGS. 3 and 5. . In the important density range of the four types of films, there is a better agreement than when the mask density is subtracted.

Therefore, the average density value of one film obtained by subtracting the photometric data of the low density portion including the mask density from the photometric value can be used as the characteristic of the image portion of each film. Further, the average value of a plurality of the above-mentioned average density values can be used for various films.

As described above, the mask density or a low density close to it, that is, the data obtained by subtracting the minimum density data other than the color film image recording area or the minimum density data of the color film image recording area from the average density is irrespective of the film type. The three color photometric data are similar. Therefore, in the present invention, the photometric data of the low density portion in the color film including the image recording portion is subtracted from the three-color photometric data obtained by dividing the color film on which the image is recorded into a large number and measuring the photometric value. The three-color corrected photometric data is obtained by correcting the color photometric data with the low-density area photometric data. The three-color corrected photometric data is converted into three-color standardized data by being standardized in accordance with a predetermined conversion condition. The three-color standardized data is classified by being compared with a reference value, the three-color photometric data is selected according to this classification, and the exposure amount is determined based on the average value of the selected three-color photometric data.

Since the mask densities do not match for each film type as described regarding the mask densities, the low-density portion photometric data should be determined for each type of color film.

〔The invention's effect〕

As described above, according to the present invention, the exposure amount is determined using the three-color corrected photometric data obtained by correcting the three-color photometric data obtained by photometrically measuring the color film with the low-density area photometric data in the color film. However, since the three-color corrected photometric data is approximate regardless of the film type, it is possible to determine the exposure amount of each film by the reference film type exposure amount without using the film type information. The effect is obtained.

Further, the photometric data of the low density portion in the color film can be obtained without photometrically measuring one film, so that there is an effect that a high-speed printing process can be performed.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 8 shows a schematic diagram of an automatic printer in which the present invention can be implemented. A lamp house 10 having a mirror box 18 and a halogen lamp is arranged below the color negative film 20 loaded in the negative carrier and conveyed to the printing unit. A dimming filter 60 is arranged between the mirror box 18 and the lamp house 10. As is well known, the light control filter 60 is composed of three filters, a Y (yellow) film, an M (magenta) film and a C (cyan) filter.

Above the negative film 20, a lens 22, a black shutter 24, and a color paper 26 are arranged in order, and the light rays emitted from the lamp house 10 and transmitted through the dimming filter 60, the mirror box 18, and the negative film 20 are lens 22. To form an image on the color paper 26.

A photometer 28 in a direction tilted with respect to the optical axis of the imaging optical system and at a position where the image density of the negative film 20 can be measured.
Is arranged. The photometer 28 is composed of a two-dimensional image sensor, a line sensor, etc., and as shown in FIG. 9, the negative image is surface-divided into a large number of pixels Sn and photometry is performed along the scanning line SL. In this case, photometry of each pixel is performed for B, G, and R3 primary colors.

The photometer 28 is connected to an arithmetic circuit 30 composed of a microcomputer or the like for calculating the exposure amount for printing. The arithmetic circuit 30 includes a memory 34 for storing data and an arithmetic circuit.
An exposure amount control circuit for controlling the printing exposure amount by controlling the dimming filter 60 based on the exposure amount calculated in 30.
42 is connected.

Next, the exposure amount calculation routine by the calculation circuit 30 will be described with reference to FIG. In step 100, the three-color photometric data measured by the photometer 28 is acquired, and in step 101, it is determined whether or not the photometry at the initial stage of printing, that is, the photometry of the start image frame or the number of frames (up to about 6 frames) from the print image frame. , For photometry in the early stage of printing, proceed to step 102,
If the photometry is not in the initial stage of printing, the process proceeds to step 104. In step 102, using the average mask densities stored in advance in the memory 34, the photometric data MI of the three low-density areas is calculated as follows.
N (R), MIN (G), MIN (B) are calculated and stored in the memory 34. The average mask density is obtained by averaging the mask density or average minimum density of various films. A value larger than the average mask density by a predetermined value α (for example, a value of 0 to 0.6) is compared with the lowest density value of the three-color photometric data or the average value of the three-color photometric data, and (average mask density + α)> (three In the case of the lowest density value of the color photometric data or the average value of the three-color photometric data), the lowest density value of the three-color photometric data or the average value of the three-color photometric data is used as the low-density portion photometric data. On the other hand, when (average mask density + α) <(lowest density value of three-color photometric data or average value of three-color photometric data), a value larger by a predetermined value α than the average mask density is used as low-density portion photometric data.

As shown in FIG. 10, the photometric area 32 of the photometer 28
The lowest density value of the three-color photometric data when the photometry is carried out in the state of straddling the image frames 20A and 20B may be the low-density portion photometric data. Further, the mask density, which is the low-density portion photometric data for each film type, is stored in advance in the memory 34, and the film type is determined by detecting a so-called DX code indicating the film type, and the low density is determined for each film type. Part photometric data may be defined.

Since low-density area photometric data is determined as described above,
This low-density portion photometric data may be the lowest density data of the image recording portion of the color film or the lowest density data (mask density) other than the image recording portion of the color film. This low-density portion photometric data is determined by photometry of the printing start image frame or several frames (up to about 6 frames) from the printing start image frame, so that the printing process speed can be increased.

In the next step 104, the three-color corrected photometric data R, G, B are calculated by subtracting the low-density area photometric data MIN (R), MIN (G), MIN (B) from each of the three-color photometric data. . As described above, the corrected photometric data has similar characteristics regardless of the film type.

In the next step 106, the corrected photometric data R and B are added to the 11th
The three-color standardized photometric data is calculated by converting to the density of G and standardizing (normalizing) using the standardization table shown in the figure. In this standardization, the film density and gradation balance differ depending on the film type and development process, so that when shooting the same subject, the image density and color will differ depending on the film type and development process. With respect to the same subject, this is a process for making the density and color constant on the negative film regardless of the film type and the developing process. Further, this standardization table is used for the photometric data G selected in step 110 described below and stored in the memory.
Is created on the basis of a curve showing the relationship between the average value of the photometric data R and the average value of the photometric data R, and a curve showing the relationship between the average value of the photometric data G and the average value of the photometric data B. The corrected using the normalization table photometric data R, while B is converted to the concentration of G, as shown in FIG. 11, for example, the average value ₃ of the correction photometric data R ₂ to R ₃ is G ₂ and is converted to an average value ₃ and G _3, the average value ₃ of the correction photometric data of B ₂ .about.B ₃ is also similarly converted into the average value _3. At this time, the corrected photometric data G is used as it is without conversion. As this standardization method, in addition to the above, JP-A-56-1039 and JP-A-62-1441
The method described in Japanese Patent No. 58 can be used.

By standardizing the corrected photometric data, the same color coordinates can be used even if the film density and film type are different, and the origin of the coordinates can be set to an arbitrary color. Assuming that the average value of the photometric data of a large number of films is gray, the standardized data of the gray subject will be the same for all three colors. Actually, the average value of the photometric data of a large number of films is slightly different from that of gray, so that the amount corresponding to the difference is corrected. The above-described standardization processing is for normalizing the sensitivity balance and the gradation balance of the film, but is not limited to this. For example, it may simply be standardized to one of the above.

Next, in step 108, as shown in FIG. 12, the difference R−G between the standardized data R and G is taken as the horizontal axis, and the standardized data G,
The difference G-B and B defined on the color coordinates of the vertical axis, the color region A _a, three color normalized data in any color region in the color region A _a non-color area A _b belongs including the origin The three-color standardized data is classified by determining whether or not. The three-color standardized data will be classified at the boundary between the color area A _a and the color area A _b . Therefore, the three-color standardized data belongs to the area where the color difference from the reference value (origin) is small. And data belonging to a region having a large color difference from the reference value.

The following table shows an example of color areas, three-color standardized data classified for each color area, and three-color photometric data corresponding to the three-color standardized data.

In the above description, the three-color standardized data is classified using the color coordinates with GB and RG as the axes, but one of the three primary colors is classified.
Color or two colors or more combination _{(e.g., D x -D y, D x} / D y,
_{D x / (D x + D} y + D z), D x + D y + D z, D x -K, D x / K , etc., provided that, x, y, z are each R, C, different one color B Where K is a constant. ) As the axis, that is, a coordinate axis having a color difference or color ratio other than the above as the axis can be used as the two-dimensional or three-dimensional color coordinate. Further, a plurality of color areas can be set according to the distance from the reference value. As the reference value, the origin of the color coordinates used, the value relating to the specific color of the original image, the value obtained from the average value of many images, the minimum value of the photometric data, the value obtained from the photometric data of the specific image, A fixed constant value or the like can be adopted. Further, the reference value may be a value given by a functional expression or a table. In this case, for example, a functional expression or a table value in which the reference value changes depending on the image density may be used. As the specific color of the original image, a neutral color, a skin color, or a color obtained from the average value of many images can be used.

Further, as the color area, a color area having an irregular distance from the origin, which is provided on the coordinate having the neutral color as the origin as shown in FIG. 13, may be used.

In step 110, the color area A with a small color difference from the reference value
_The three-color photometric data corresponding to the three-color standardized data belonging to a is selected and stored in the memory 34, and the three-color photometric data selected in step 112 are averaged to obtain the first image data MD _a.
Is calculated. When the three-color standardized data are classified by the coordinates with the color ratio as the axis, the three-color photometric data corresponding to the three-color standardized data belonging to the color area with the smaller color ratio from the reference value is selected, and the three-color photometric data are selected. First to average color photometric data
The image data MD _a of will be calculated.

In the next step 114, the second image data MD _c corresponding to a specific color (for example, a neutral color, a color having a certain color difference or a color ratio larger than the neutral color) is calculated. The second image data MD _c may use a three-color photometric data corresponding to the origin of the color coordinates shown in FIG. 12. The three color photometric data, 'When _c (G), the MD' the G density of the first image data MD _a MD is inversely transformed using a standardized table showing the _c (G) in FIG. 11 Therefore, the R concentration MD ′ _c (R),
The B concentration MD ′ _c (B) is _calculated (FIG. 14), and R, G, and B concentrations MD ′ _c (R), MD ′ are obtained as shown in the following equation (2).
_c (G), density MD ′ _c (B)
It is obtained by adding MIN (R), MIN (G), and MIN (B).

_{MD c (R) = MD '} c (R) + MIN (R) MD c (G) = MD' c (G) + MIN (G) MD c (B) = MD 'c (B) + MIN (B) ... ( 2) Then, in step 116, the exposure control value D _j of the print negative is obtained according to the following equation (3), and in step 118 the exposure amount E _j is calculated according to the following equation (4). The subscript j indicates R, G and B.

_{D j = K a · MD a} + K c MD c ... (3) logE j = C j · S j (D j -D joN) + F j + d j ... (4) However, K _a, K _c performs weighting Coefficient for K _a + K _c
≈ a constant value (for example, 1.0), C _j is a color collection coefficient (≈ 1.0), and S _j is a slope control coefficient (=
0.5 to 2.0), D _joN is the exposure control value of the reference image of the reference film type, F _j is a constant determined by the color paper and color printer, and d _j is the exposure correction amount based on the image content.

The weighting coefficient K _a, K _c may be modified as follows according to the purpose described in the following (1) to (3).

(1) setting an exposure condition when _{K a = 0.7~1.2 (0.9) K} c = 0.5~0.0 (0.1) (2) Maniyuaru printed when _{K a = 0.3~0.9 (0.7) K} c = 0.7~0.1 (0.3) ( 3) However when automatic printing _{K a = 0.7~1.2 (1.0) K} c = 0.5~0.0 (0.0), numbers in () is the desired value.

In addition, when setting the exposure conditions and at the time of manual printing, it is preferable to expand the range of the color area A _a or stop the selection of the photometric data and use all the three-color photometric data. This is the correction of the film type as the coefficient K _c increases,
Worse correction of an artificial light source becomes favorable correction of color off area, becomes opposite to the above-described in accordance with the coefficient K _a is increased,
By selecting photometric data, even if the coefficient K _a is large, color area correction, film type correction, and artificial light source correction are good, while color area correction and light source correction are performed when setting exposure conditions and during manual printing. This is because the effect of selecting the photometric data is weakened and stabilized by eliminating the need for the like.

By the way, as can be understood from FIGS. 3, 5, 6, and 7, the color balance between R and G is substantially constant depending on the density, and G and B are such that the B density relative to the G density increases as the density increases. Is getting higher. Therefore, in this case, it is necessary to know how much the photometric data is different from the photometric data of the low density portion such as the mask density. When the color balance is allowed to fluctuate by ± 0.05 (the image density of the gray subject changes depending on the photographic light source, camera, film changes over time, characteristics between lots, etc., so the standardized curve also has a fluctuation range. Error is ± 0.05), concentration (eg G
Concentration) error of ± 0.3 is acceptable. That is, if the error in the image density of the photometric data is within ± 0.3, the color balance can be predicted within ± 0.05. As a result, it suffices if the low-density portion photometric data is within ± 0.3 with respect to the mask density or the mask density + α.

In the present invention, the photometric data is standardized and a fixed predetermined comparison reference value is determined without determining the comparison reference value for the photometric data for each film strip. Since this standardization condition can be obtained from a large number of image data of one film strip or more, it is possible to obtain the standardization condition with high accuracy. As a result, highly accurate exposure control becomes possible.

Although the second image data is determined from the origin of the coordinates in FIG. 12 above, the second image data is determined from the average value of the three-color photometric data of the photometric points included in the neutral area indicated by the diagonal lines in FIG.
Image data may be determined.

It is also possible to use a data MD _'c represented by the following formula in place of the second image data MD _c.

MD ′ _c = MD _c −K _j (5) However, K _j is _a correction value that does not change the print color even if the values of _Ka and K _c are changed, and MD ′ _c is the value of each film. No color change occurs when equal to the average photometric data of the seed. Further, K _j may be changed depending on the concentration.

When the low-density area photometric data is larger than a predetermined value (in the case of an overexposure film), whether the low-density area photometric data is corrected by a predetermined method without using the low-density area photometric data. When the predetermined value is used as the low-density portion photometric data, for example, MIN '(j) = KX _j MIN (j) (6) (where KX _j is a coefficient of KX _j <1.0). It may be corrected, and the determined low-density area data of various films can be used as the determined value. The present invention can also be applied to image display devices such as digital color printers and CRTs.

[Brief description of drawings]

FIG. 1 is a flow chart showing an exposure amount calculation routine of an embodiment of the present invention, and FIG. 2 is a film image obtained by photographing a standard subject even if the exposure amount is sequentially changed with A, B, C and D4 negative films. The average density obtained by photometry is plotted on the color coordinates, FIG. 3 is the diagram showing the image density obtained by subtracting the mask density from each average density of FIG. 2 on the color coordinates, and FIG. 4 is the above. A diagram showing a large number of average densities of four types of negative films divided into four density levels and shown on the color coordinates, and FIG. 5 shows densities obtained by subtracting mask densities from the respective average values on the color coordinates. FIG. 6, FIG. 6 and FIG. 7 are diagrams showing the values obtained by subtracting the low-density portion photometric data from the average density on the same color coordinates as in FIGS. 3 and 5, and FIG. 8 is the present invention. Fig. 9 is a schematic diagram of an auto color printer to which is applied, Fig. 9 is a diagram showing the state of photometry by surface division, and Fig. 10 is A diagram showing the state of photometry of mask density, Fig. 11 is a diagram showing a standardization curve, Fig. 12 is a diagram showing color coordinates for classifying three-color standardized data, and Fig. 13 is three-color standardized. FIG. 14 is a diagram showing another color coordinate for classifying the data, and FIG. 14 is a diagram for explaining how to obtain the second image data. 26 …… color paper, 28 …… photometer, 60 …… dimming filter.

Claims (6)

(57) [Claims] 1. A three-color photometric data is obtained by dividing a color film on which an image is recorded into a large number of pieces to perform photometry,
The three-color corrected photometric data is obtained by correcting the three-color photometric data with the low-density photometric data in the color film including the image recording unit, and the three-color corrected photometric data is converted according to predetermined conversion conditions. Then, the three-color standardized data is obtained by normalizing the three-color standardized data, and the three-color standardized data is compared with a reference value to classify the three-color standardized data. An exposure amount determining method for an image copying apparatus, which selects color photometric data and determines the exposure amount based on an average value of the selected three-color photometric data. 2. The exposure amount determining method for an image copying apparatus according to claim 1, wherein the low-density portion photometric data is determined for each type of color film. 3. The three-color standardized data is classified by determining which one of a plurality of areas on a predetermined two-dimensional or three-dimensional coordinate the three-color standardized data belongs to. An exposure amount determining method for an image copying apparatus according to item (1) or (2). 4. The exposure amount determining method for an image copying apparatus according to claim 1, wherein the low-density portion photometric data is minimum density data of an image recording portion of a color film. 5. The exposure amount determining method for an image copying apparatus according to claim 1, wherein the low-density area photometric data is minimum density data other than that of an image recording area of a color film. . 6. The image according to claim 1, wherein the low-density area photometric data is minimum density data of an area recorded on a color film and straddling adjacent images. Exposure amount determination method for copying machine.