JPS6261132B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for classifying color originals and a method for color correction, in which a color image that causes color fade is detected from among color originals, and color correction is performed on the color original at the time of printing. It is empirically known that in a standard color original picture, the blue, green, and red components of the light transmitted through the entire screen are approximately equal (Evans' principle). Therefore, most color printers measure large-area transmission density for each color, and perform color correction by controlling the amount of printing light in accordance with this measured value. With this LATD color printer, for standard color originals with almost equal three color components,
Printed photographs with appropriate density and good color balance can be obtained. However, it is not possible to produce a printed photograph with good color balance from a color original image with unbalanced color balance. Therefore, the reality is that only for those items that are defective in printing, the operator selects a color key based on visual and shape judgment and reprints them. Additionally, a method has been proposed in which the hue of the large area average transmission density (LATD) is examined to detect the occurrence of color areas. However, this method of LATD, which makes judgments based only on the hue, is not accurate because false judgments occur. For example, if we take yellow as an example, there are two cases: a case where the screen is purely yellow, and a case where there are approximately half red and half green, resulting in a total yellow screen.
Judging only by the hue of LATD, both are yellow and their hues match. The former does not produce color areas;
Since the latter causes a collarf area,
It is necessary to distinguish between the two, but it cannot be done only by the hue of LATD. The present invention provides a color original image classification method and color correction method that accurately detects those that cause color areas from color original images, and performs color correction on the color original images to improve color balance. The purpose is to The classification method of the present invention measures the blue, green, and red densities of the entire screen of a color original image and many points in the screen, and calculates characteristic values on two-dimensional color coordinates created by the combination of blue, green, and red densities. The color indicated by the measured overall screen average density is determined by the angle and the distance from the center coordinates, and the area ratio of each color of red, green, yellow, and blue in the screen is calculated, and the screen average density is determined to be a predetermined value. Regarding the color original image in which images smaller than the above are excluded as underexposed, the distance to the angle and the area ratio of the color corresponding to the angle are larger than a predetermined value, and the color area is generated. This feature is characterized in that it is classified as something that does not occur. Therefore, since we use the difference in the area ratio of two colors, we can distinguish between those that tend to produce color areas and those that do not, for example, those that are a mixture of red and green to form a yellow hue, and those that are pure yellow. can be accurately identified. Here I will explain why I chose red, green, yellow, and blue as specific colors. Color areas often occur when the color is highly concentrated and occupies a relatively large area. As a result of examining about 30,000 frames, it was found that red is most commonly used in artificial colors (clothing, shrines, chicks, etc.), flowers, etc., and is most likely to cause color fade. Green is overwhelmingly the leaves of plants, lawns, etc., and there are many subjects to photograph. Blue is often seen in the sea, sky, and artificial colors (clothing, etc.), and yellow is often seen in artificial colors (clothing, etc.), flowers, and gold at weddings. If you want to make it even more detailed, add magenta. In other words, azaleas in early spring correspond to these. Therefore, it has been found that if color correction is performed for these specific colors, most color area corrections can be covered. A preset color key or lower word correction is applied to the color original image in which color areas occur, and color correction is performed. Embodiments of the present invention will be described in detail below with reference to the drawings. FIG. 1 schematically shows an apparatus for carrying out the present invention. The measurement unit 10 measures the amount of transmitted light over the entire color original image and at each point. Measuring section 10
is equipped with a flying spot scanner that scans color originals two-dimensionally and measures the amount of transmitted light at 560 measurement points. Specifically, a disk is used in which a large number of light transmitting holes at different distances from the center are separated with a predetermined phase, and by rotating this disk, light of 1 mmφ or less is passed through each light transmitting hole. A color original is scanned using a spot light. 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. As a result, blue density B, green density G, and red density R are measured at 560 measurement points on the color original image. In addition, a rectangular opening is formed in the disc that can illuminate the entire surface of the color original image, and this opening allows LATD _W and its hue (LATD _B ,
LATD _G , LATD _R ) are measured. Furthermore, this
Instead of LATD, an average value obtained from the measured values at each point may be used. Blue density B at each point obtained by the measurement unit 10,
The green density G, red density R, LATD _W , and the hue of LATD are sent to a characteristic value calculating section 11, where characteristic values such as area ratio of a specific color are calculated. These characteristic values are sent to the determination unit 12 and compared with reference values for distinguishing between those in which color rays occur and those in which they do not. Next, a conditional expression for distinguishing between cases in which color areas occur and cases in which color areas do not occur will be explained. The LATD _W is used to remove underexposed images from the color original image. That is, an underexposed image cannot have an accurate hue due to the curvature of the characteristic curve of the photosensitive material. Therefore, if such things are judged, erroneous judgments will occur, so the 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. In the case of red faeria, the hue of LATD becomes biased due to the influence of red. 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 the angle θ with the horizontal axis as the starting line and the distance ρ from the origin. Using these ρ and θ, the hue of LATD is expressed as Lρ and Lθ,
In the case of the R area, the following conditional expression is satisfied. Lρ≧Lρ ₁ ∩Lθ _r ≦Lθ≦Lθ ₂ (2) Here, Lρ ₁ , Lθ ₁ , and Lθ ₂ are reference values determined through experiments. In addition, in the case of a red area, the area ratio of red is considerably large, and there is a difference between the area ratio of blue (in this case, it includes a considerable cyan area, so it is possible to represent blue as a complementary color). . Therefore, the following conditional expression is satisfied. n _RB = n _1R - n _2B ≧ α (3) where α is a reference value determined by experiment. It is also possible to make a determination based on a single area ratio without using the difference in area ratio with a complementary color, although the accuracy is lower. The area ratio is expressed as n/N, where N is the total number of measurement points and n is the number of points determined to be a specific color. Therefore, if N is constant (for example, 560), the number n can be used instead. The above formula (3) uses the number n, and n _1R
represents the number of red dots, and n _2B represents the number of blue dots. Certain colors such as red and blue are two-dimensional or three-dimensional.
The area is defined in terms of dimensional coordinates, and when a measurement point is included in this area, that point is determined to be of a specific color. 25,000 color negative films shot in one year
We investigated the characteristic values of the pieces and determined the standard values experimentally. Using this standard value, the above formula (1) ~
(3) becomes as follows. LATD≧0.3 …(1) Lρ≧0.2 330゜≦Lθ≦65゜ …(2) n _RB ≧30 …(3) Since the value of n _RB represents the size of the red area, this It is desirable to perform color correction by selecting a color key depending on the value. Table 1 shows the relationship between _nRB and color key.

[Table] Furthermore, in the case of the G area, the same conditional expression as the above R area holds true. That is, LATD≧0.3 …(4) Lρ≧0.2∩100゜≦Lθ≦150゜ …(5) n _G ≧100 …(6) For B area, LATD≧0.3 …(7) Lρ≧0.2∩ 200゜≦Lθ≦250゜ ...(8) n _BY =n _B -n _Y =150 ...(9) For Y area, LATD≧0.3 ...(10) Lρ≧0.2∩65゜≦Lθ≦85゜...(11) n _YB = n _Y - n _B = 150 ...(12) Based on the above equations (1) to (12), color originals are classified into those that cause color fade and those that do not. be done. However, it is not necessary to adopt all of them depending on their importance. For a color original image that is determined to have a color area, the color key of the color supplement key 13 or the lower word collection mode is selected. In these color correction keys or lower correction modes, a predetermined amount of color correction is determined depending on the type and degree of the color area. Color original image classification device and color printer 14
If it is connected online, it will be printed in the selected color key or lower word collection mode. For those that are offline, information on the selected color correction key is stored in the storage unit 15 such as magnetic tape or paper tape. FIG. 2 shows a flowchart of the determination section for classifying red color areas. At judgment L1, equation (1)
A determination is made as to whether LATD _W is greater than or equal to 0.3. When the answer to this judgment L1 is "YES", it is determined in judgment L2 whether or not the expression (2), Lρ≧0.2∩330°≦Lθ≦65°, is satisfied. When the answer to judgment L2 is “YES”, judgment L3
It is determined whether n _RB ≧30 in equation (3) is satisfied. When the answer to this judgment L3 is YES, it is determined that the color original image causes a color area (red area). If the answer to judgments L1 to L3 is "NO", it is determined that the color field does not occur and is sent to the next judgment step for other classification. The present invention having the above configuration uses, in addition to the LATD hue, the difference in area ratio between a specific color (red, blue, green, yellow) and its complementary color as a characteristic value. It is possible to accurately distinguish between those that occur and those that do not. In addition, since a color original image determined to have a color area is printed using a lower word collection or a preset color key, a printed photograph with good color balance can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus for carrying out the present invention;
FIG. 2 is a flowchart of the determination section that determines the R area.

Claims (1)

[Claims] 1 Measure the blue, green, and red densities of the entire screen of the color original image and many points on the screen, and
On the two-dimensional color coordinates created by the combination of red densities, the color indicated by the measured overall screen average density is determined by the angle and distance from the center coordinate as a characteristic value, and each color of red, green, yellow, and blue is calculated as a characteristic value. The distance to the angle and the area ratio of the color corresponding to the angle are predetermined values for the color original image in which the area ratio in the screen is calculated and images whose screen average density is smaller than a predetermined value are excluded as underexposed. A method for classifying color originals, characterized in that originals larger than the original size are classified as ones with a color area and those without a color area.