JPS6321178B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a color original image classification method and a color correction method in which color original images photographed under tungsten light are detected and color correction is performed at the time of printing. It is empirically known that in a standard color original picture (for example, a color negative film), the three color light components of blue, green, and red are approximately equal (Evans' principle). Therefore, most color printers
Based on this Evans principle, each color
The LATD is measured and the printing exposure amount is controlled according to this measurement value. However, the LATD method described above can produce printed photographs with appropriate density and good color balance for standard color originals in which the three color light components are approximately equal; It is not possible to perform good color correction on colors that used to have a yellowish tinge. Therefore, in the past, the operator's visual perception was limited only to defective prints due to extreme color defects.
The reality is that color correction is performed by selecting a color key based on shape judgment. In view of the above circumstances, the present invention detects a color original photographed under tungsten light, performs predetermined color correction on this color original, and obtains a printed photograph with good color balance. The purpose of this invention is to provide a classification method and a color correction method for original images. Various characteristic values were investigated for a large number of color originals. As a result, the hue of the screen average density (LATD or the average value calculated from each point), the hue of the highest density point, the area ratio of points included in the color area on the defined two-dimensional color coordinates including skin color, and the average hue Then, by determining the area ratio of gray and yellow points, and using these characteristic values to see whether they fall within a predetermined range representing photography under tungsten light, it is possible to identify tungsten light from among a large number of color originals. We found that it is possible to accurately classify items that have a large impact. The specific colors include gray and yellow. These areas are predefined on the coordinates,
When a measurement point is included within this area, that point is determined to be of a specific color. Color originals taken under tungsten light are printed using a high correction that finishes the entire image in gray, or using a preset color key. The present invention will be explained in detail below. FIG. 1 shows an apparatus for carrying out the invention. The measurement unit 10 measures the amount of transmitted light or reflected light at each point on the entire screen of the color original image. The color original is scanned two-dimensionally with a flying spot scanner and measured at 560 measurement points. Specifically, a disk is used in which a large number of light transmitting holes are formed at different distances from the center and separated at a predetermined phase. This disk is rotated and the original color image is illuminated with spot light of 1 mm diameter or less that passes through each light transmission hole. The light that passes through the color original is separated into three colors, blue, green, and red, by a dichroic mirror, and then enters each photo. The output of this photomal is logarithmically transformed and then sampled by a sampling circuit. the result,
Blue density B, green density G, and red density R are each measured at 560 measurement points on the color original image. In addition, a rectangular opening is formed on the disk that can illuminate the entire surface of the color original.
This aperture allows LATD _W (density due to white light)
and LATD hue (LATD _B , LATD _G , LATD _R )
is measured. Note that the average value calculated from each point can be used instead of the hue of LATD _W and LATD. The three color densities at each point obtained by the measuring section 10 are:
The data is sent to the characteristic value calculation unit 11, where the area ratio and hue of a specific color, such as skin color, gray, yellow, etc. under tungsten light, the hue of the maximum density point, etc. are calculated. The characteristic values calculated by the characteristic value calculating section 11 are sent to the determining section 12 and compared with a reference value for distinguishing between those photographed under tungsten light and those not photographed. As a result of these comparisons, if a predetermined condition is satisfied, it is determined that the light source is tungsten light. Next, a determination conditional expression will be listed and explained. LATD _W is used to remove underexposed images from color originals. That is, an underexposed image cannot have an accurate hue due to the curvature of the characteristic curve of the photosensitive material. Therefore, if even such things are judged, erroneous judgments will occur, so underexposed ones are removed in advance. Since LATD _W represents the brightness of the entire screen, a color original image that is not underexposed satisfies the following conditions. LATD _W ≧U ₁ ...(1) Here, U ₁ is a reference value determined by experiment. When photographing under tungsten light, the LATD hue is often distributed within a certain range due to the color of the light source. With G-B as the vertical axis, R-
In two-dimensional coordinates with G on the horizontal axis, the hue of any point can be expressed by an angle θ with the horizontal axis as the starting line and a distance ρ from the origin. Therefore
When the hue of LATD is expressed by Lρ and Lθ, a color original photographed under tungsten light satisfies the following conditions. Lρ≧Lρ ₁ ∩Lθ ₁ ≦Lθ≦Lθ ₁ (2) Here, Lρ ₁ , Lθ ₁ , and Lθ ₂ are reference values determined by experiment. In color original images photographed under tungsten light, the point of maximum brightness (highest density on the color original image) is often the light source color. Therefore, by checking the hue at the highest density point, it is possible to know whether the light source is tungsten light. If the hue at the highest density point is DMθ, then the image under tungsten light satisfies the following conditions. DMθ ₁ ≦DMθ≦DMθ ₂ (3) Here, DMθ ₁ and DMθ ₂ are reference values determined by experiment. More than 80% of color original paintings have people as the main subject. The hue of this person's skin varies depending on the color of the light source. The skin-colored area under the tungsten light can be defined as an ellipse or an ellipsoid in two-dimensional or three-dimensional coordinates, or more simply, as a sector as shown in FIG. 3. When the hue of the measurement point is included in this ellipsoid or sector,
This point is determined to be the skin color under tungsten light. If tungsten light is the light source color, there should be a large number of measurement points that are judged as skin color under tungsten light, so you can distinguish between those under tungsten light and those without. can do. Also, under tungsten light, if the average hue of skin color under tungsten light (average hue of points determined to be skin color under tungsten light) is FTX (X = RG), this
FTX exists in a certain range. Therefore,
The light source color can be determined by examining the number and average hue of skin colors under tungsten light. However, since there are cases where the person is small or absent, it is better to set this judgment condition within a wide range. nST≧α ₁ ∩FTX≧FTX ₁ (4) where nST is the number of points determined to be skin color under tungsten light. Note that this number is used instead of the area ratio n/N.
That is, once the total number N (for example, 560) of measurement points is determined, the area ratio can be expressed by the number n. In addition, color originals under tungsten light are gray for the following reason: the achromatic parts (i.e., gray parts) of the subject shift in the direction of a specific hue due to the light source color; The number of objects is extremely small, i.e. nGray≦α ₂ ...(5) Also, when photographing objects with a lot of yellowish tinge, such as flowers and clothes,
When viewed with LATD, it is easy to be mistaken for judgment under tungsten light as defined by LATD. Therefore, these can be identified by the number of yellow colors. nY≦α ₃ ...(6) Here, nY is the number of points determined to be yellow,
α ₃ is a reference value determined by experiment. Furthermore, it can be said that the number of measurement points determined to be the skin color under daylight is smaller when measured under tungsten light. Therefore, if the skin color under daylight is taken into account, the detection accuracy will be further improved. Note that the skin color under daylight may be determined to be a similar color, so it is not actually zero. nSF≦α ₄ ...(7) Here, nSF is the number of measurement points determined to have skin color under daylight. The above conditional expressions (1) to (7) are enumerated as follows. LATD _W ≧U ₁ …(1) Lρ≧Lρ ₁ ∩Lθ ₁ ≦Lθ≦Lθ ₂ …(2) DMθ ₁ ≦DMθ≦DMθ ₂ …(3) nST≧α ₁ ∩FTX≧FTX ₁ … (4) nGray≦α ₂ …(5) nY≦α ₃ …(6) nSF≦α ₄ …(7) If all of these conditional expressions are satisfied, the light source is determined to be tungsten light. Ru. 25,000 color negative films shot in one year
The standard values were determined experimentally by examining the characteristic values of the pieces. Using these reference values, Equation (1)
~(7) becomes as follows. LATD _W ≧0.3 ……(1) Lρ≧0.2∩40゜≦Lθ≦100゜ ……(2) 4゜≦DMθ≦100゜ ……(3) nST≧10∩FTX≧0.30 ……(4) nGray ≦100 ...(5) nY≦100 ...(6) nSF≦100 ...(7) Using the above conditional expressions, color originals are classified into those under tungsten light and those under tungsten light. In this embodiment, even if images are taken under tungsten light, underexposed images are excluded, and a separate color correction is performed on these images. If it is determined that the photograph was taken under tungsten light, the high collection mode of the color correction key 13 is selected. If the color original classification device and the color printer 14 are connected online, the selected high collection correction key is used to print. For those that are offline, information on the selected correction key is recorded in the storage unit 15 such as paper tape or magnetic tape. FIG. 2 is a flowchart of the determination section 12.
In judgment L1, it is determined whether the condition of equation (1), that is, LATD _W is 0.3 or more. When the answer to judgment L1 is “YES”, judgment L2
It is determined whether Lρ≧0.2∩40°≦Lθ≦100° in equation (2) is satisfied. When the answer to judgment L2 is “YES”, judgment L3
It is determined whether the equation (3) of 4°≦DMθ≦100° is satisfied. When the answer to judgment L3 is “YES”, judgment L4
It is determined whether nST≧10∩FTX≧0.30 in equation (4) is satisfied. When the answer to judgment L4 is “YES”, judgment L5
It is determined whether nGray≦100 in equation (5) is satisfied. When the answer to judgment L5 is “YES”, judgment L6
It is determined whether nY≦100 in equation (6) is satisfied. When the answer to judgment L6 is “YES”, judgment L7
It is determined whether nSF≦100 in equation (7) is satisfied. When the answer to the above judgment L7 is "YES", all the conditions are satisfied, so the light source of the color original image is determined to be tungsten light, and the high collection mode is selected. If the answer to each of the judgments L1 to L7 is "NO", it is determined that the light source is not tungsten light, and the light source is sent to the next judgment step for other classification. The tungsten light objects were classified using the conditional expression of the present invention, and these objects were printed in high collection mode. The results are shown in Table 1. Here, correct correction refers to correction in the correct direction and good color balance.
Reverse correction refers to correction in the opposite direction, resulting in poor color balance.

[Table] In the conventional LATD method, color correction is not performed at all for 33 frames under tungsten light, but in the present invention, these are classified and color corrected, so 25 of them are color balanced. has improved. According to the present invention having the above configuration, objects photographed under tungsten light can be classified with high accuracy. And for these color originals,
Since color correction is performed using the high collection mode or a preset color key, printed photos with good color balance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an outline of an apparatus for carrying out the present invention, FIG. 2 is a flowchart of the determination section, and FIG. 3 is a fan-shaped representation of a skin-colored area in two-dimensional coordinates.

Claims (1)

[Claims] 1.Measure the blue, green, and red densities of many points on the screen of the color original picture, calculate the screen average density,
Regarding the color original image in which images whose screen average density is smaller than a predetermined value are excluded as underexposed,
Characteristic values include the hue of the screen average density, the hue of the highest density point, the area ratio of points included in the color area on the defined two-dimensional color coordinates, including the skin color under tungsten light, its average hue, and gray and yellow points. The area ratio of tungsten light is determined, and those taken under tungsten light are classified from among a large number of color originals based on whether or not these characteristic values are within a predetermined range representing photography under tungsten light. A classification method for color originals featuring the following.