CN115147345A - Method and system for calculating image color difference - Google Patents

Abstract

The invention provides a method and a system for calculating image chromatic aberration, and relates to the technical field of printed image chromatic aberration processing. The method for calculating the image color difference comprises the following steps: acquiring a target image and a printing image of the target image; performing color space conversion on the target image to obtain at least one first primary color image, and performing color space conversion on the printing image to obtain at least one second primary color image; a first primary color image corresponds to a second primary color image; the first primary color image and the second primary color image are both images in a printing color mode; calculating the color coverage rate of each first primary color image and the color coverage rate of each second primary color image; and comparing the color coverage rate of the first primary color image with the corresponding color coverage rate of the second primary color image to obtain the color difference value of each second primary color image. The invention can realize the requirement of quantitatively describing the color difference of the image.

Description

Method and system for calculating image color difference

Technical Field

The invention relates to the technical field of printed image color difference processing, in particular to a method and a system for calculating image color difference.

Background

In the printing industry, especially in the printing production process of a single-sheet offset press, because the problem of color difference between two images cannot be quantified, the production process of manually viewing a sample is used up to now, a printing machine operator finds the color difference between a printed product and the sample by observing the sample by naked eyes, then manually adjusts the given amount of CMYK four-color ink of the printing machine, so as to change the color of the printed product, performs the color comparison of the printed product and the sample by naked eyes after printing hundreds of printed products in a trial way, performs the manual adjustment if the color difference exists, then performs the trial printing of hundreds of printed products, and repeats the process in the production process of a single printed product repeatedly for many times, thereby wasting time and paper, and the higher the requirement on the color accuracy of the printed product is, and the longer the manual adjustment process is, the more the wasted paper is needed.

As is well known, the traditional method of evaluating the difference between two colors is to use a spectrocolorimeter, which is illuminated by a built-in standard light source onto the color patch to be measured, records the reflected light spectrum and converts the spectral signal into an absolute color Lab value. The color difference value of the two color blocks is obtained by calculating the absolute distance between the Lab values of the two color blocks in a color space, and the method is a method for measuring the color difference between the two colors commonly used in the industry at present.

Although accurate absolute color difference values can be obtained using a spectrocolorimeter, the disadvantages of this approach are also apparent. One is that the price of the equipment is expensive, and the market price is about 5 ten thousand RMB; secondly, the area requirement of the color block of the measuring object is large, the size and the diameter of the color block of the measured color are generally required to be more than 3mm, the color difference of the color block with the large area is only limited by using the spectrometer for measuring the color, and the color difference of images such as photos and the like is not well realized at present.

Because the size of each pixel in the image is only micrometer level, and the color of each pixel is different, at present, human eyes are usually adopted to observe whether two pictures with the same content have obvious chromatic aberration, but no instrument is used for measuring and obtaining the datamation chromatic aberration description. Therefore, the existing image color difference calculation method cannot quantitatively describe the image color difference.

Disclosure of Invention

The invention aims to provide a method and a system for calculating image color difference so as to meet the requirement of quantitatively describing the image color difference.

In order to achieve the purpose, the invention provides the following scheme:

a method of calculating image color differences, the method comprising:

acquiring a target image and a printing image of the target image;

performing color space conversion on the target image to obtain at least one first primary color image, and performing color space conversion on the printing image to obtain at least one second primary color image; one said first primary color image corresponding to one said second primary color image; the first primary color image and the second primary color image are both images in a printing color mode;

calculating the color coverage rate of each first primary color image and the color coverage rate of each second primary color image;

and comparing the color coverage rate of the first primary color image with the corresponding color coverage rate of the second primary color image to obtain the color difference value of each second primary color image.

Specifically, after the comparing the color coverage of the first primary color image with the color coverage of the corresponding second primary color image to obtain the color difference value of each second primary color image, the method further includes:

and correcting the corresponding second primary color image according to the color difference value.

Specifically, before the performing color space conversion on the target image to obtain at least one first primary color image, and performing color space conversion on the print image to obtain at least one second primary color image, the method further includes:

adjusting the resolution of the target image and the resolution of the printed image to a set resolution value.

Specifically, the calculating the color coverage of each first primary color image and the color coverage of each second primary color image specifically includes:

for any one of the first primary color images, dividing the first primary color image into a plurality of first primary color regions, calculating the color value of each first primary color region, and determining the average value of the color values of all the first primary color regions as the color coverage of the first primary color image;

for any one of the second primary color images, dividing the second primary color image into a plurality of second primary color regions, calculating the color value of each second primary color region, and determining the average value of the color values of all the second primary color regions as the color coverage of the second primary color image.

Specifically, the comparing the color coverage of the first primary color image with the color coverage of the corresponding second primary color image to obtain the color difference value of each second primary color image specifically includes:

and the color coverage rate of the first primary color image is different from the color coverage rate of the corresponding second primary color image, so that the color difference value of each second primary color image is obtained.

A system for calculating image color differences, comprising:

the image acquisition module is used for acquiring a target image and a printing image of the target image;

the image conversion module is used for performing color space conversion on the target image to obtain at least one first primary color image, and performing color space conversion on the printing image to obtain at least one second primary color image; one said first primary color image corresponding to one said second primary color image; the first primary color image and the second primary color image are both images in a printed color mode;

the color coverage rate calculation module is used for calculating the color coverage rate of each first primary color image and the color coverage rate of each second primary color image;

and the color difference calculating module is used for comparing the color coverage rate of the first primary color image with the color coverage rate of the corresponding second primary color image to obtain the color difference value of each second primary color image.

Specifically, the method further comprises the following steps:

and the image correction module is used for correcting the corresponding second primary color image according to the color difference value.

Specifically, the method further comprises the following steps:

and the resolution adjusting module is used for adjusting the resolution of the target image and the resolution of the printing image to a set resolution value.

Specifically, the color coverage calculation module includes:

the first calculation sub-module is used for dividing the first primary color image into a plurality of first primary color areas for any one first primary color image, calculating the color value of each first primary color area, and determining the average value of the color values of all the first primary color areas as the color coverage rate of the first primary color image;

and the second calculation submodule is used for dividing the second primary color image into a plurality of second primary color areas for any one second primary color image, calculating the color value of each second primary color area, and determining the average value of the color values of all the second primary color areas as the color coverage rate of the second primary color image.

Specifically, the color difference calculation module specifically includes:

and the third calculating submodule is used for subtracting the color coverage rate of the first primary color image from the corresponding color coverage rate of the second primary color image to obtain the color difference value of each second primary color image.

According to the specific embodiment provided by the invention, the invention discloses the following technical effects:

according to the method and the system for calculating the image color difference, provided by the embodiment of the invention, the target image and the printing image of the target image are obtained, then the color space conversion is respectively carried out on the target image and the printing image, the target image and the printing image are converted into the printing color mode, then the color coverage rate is calculated and compared to obtain the color difference value, so that the color difference between the printing image and the target image is determined, and the requirement of quantitatively describing the image color difference is realized.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required in the embodiments will be briefly described below, and it is obvious that the drawings in the following description are only some embodiments of the present invention, and it is obvious for those skilled in the art that other drawings can be obtained according to these drawings without creative efforts.

FIG. 1 is a flowchart of a method for calculating chromatic aberration of an image according to an embodiment of the present invention;

FIG. 2 is a diagram of a specific implementation process of a method for calculating image color difference according to an embodiment of the present invention;

fig. 3 is a structural diagram of a system for calculating chromatic aberration of an image according to an embodiment of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

The invention aims to provide a method and a system for calculating image color difference.

In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in further detail below.

As shown in fig. 1, the method for calculating the image color difference of the present embodiment includes:

step 100: a target image and a print image of the target image are acquired. In particular, a digital camera or scanner may be used to capture images that need to be compared (e.g., the target image and a printed image of the target image).

Step 200: and performing color space conversion on the target image to obtain at least one first primary color image, and performing color space conversion on the printed image to obtain at least one second primary color image.

Performing color space conversion on the target image for color separation, wherein the color space conversion uses an International Color Consortium (ICC) color profile for color separation to obtain at least one first primary color image; similarly, performing color space conversion on the printed image to obtain at least one second primary color image; a first primary color image corresponds to a second primary color image; the first primary color image and the second primary color image are both images in a printed color mode.

Image conversion color space, i.e. the color space conversion of an image, usually RGB to CMYK, in a printing Color Mode (CMYK), all colors of the image are decomposed into four primary colors cyan (C), magenta (M), yellow (Y) and black (K); here, color space conversion is performed to perform color separation by using the color profile ICC, and in the process of color separation of two contrast images, that is, a target image and a print image of the target image, it is necessary to keep the two contrast images separated by using the same color profile.

Step 300: the color coverage of each first primary color image and the color coverage of each second primary color image are calculated.

Step 400: and comparing the color coverage rate of the first primary color image with the corresponding color coverage rate of the second primary color image to obtain the color difference value of each second primary color image.

In one embodiment, as shown in fig. 2, step 600 is further included after comparing the color coverage of the first primary color image and the corresponding color coverage of the second primary color image in step 400 to obtain the color difference value of each second primary color image.

Step 600: correcting the corresponding second primary color image according to the color difference value; and image correction is carried out according to the color difference value, and the color difference value of each primary color is corrected respectively based on the color difference value between the primary colors, so that the colors of the two images are consistent.

In one embodiment, as shown in FIG. 2, at step 200: step 500 is also included before color space converting the target image to obtain at least one first primary color image and color space converting the print image to obtain at least one second primary color image.

Step 500: the resolution of the target image and the resolution of the printed image are adjusted to set resolution values. That is, the captured digital image, i.e., the target image and the print image of the target image, are adjusted in resolution in the computer, where 72dpi is available, a moderate resolution to achieve a balance between accuracy and processing speed.

The image is bitmap, the pixel size of the image depends on the image accuracy, and a 72dpi image, with 72 pixels distributed over an inch length, then 5184 pixels (pixels) in a1 square inch area, each pixel (pixels) having a respective CYMK value (this value represents the color depth, ranging from 0-100 to represent the shade and shade tone variation of the primary color, 0 represents the absence of the primary color, and 100 represents the deepest of the primary color). If the CMYK color values of the same pixel (pixels) of the two pictures are the same, the color of this pixel is assumed to be the same. Of course, the color values of all the pixel points of the two images cannot be compared, and even if the color values of a certain pixel point in the image are different, the difference of the colors in the visual sense of the whole image cannot be judged.

In order to approximate the judgment of color difference of the image by visual sense, for example, the judgment of the image color by human eyes is based on the whole image range, namely, the judgment of the whole area of the image, and the human eyes cannot judge the color value of the pixel color. Even if a computer is used to perform pixel-level comparison between two pictures, the positioning accuracy of the images is a big problem, and the positioning difference between two identical pixels, for example, 4000dpi and 3000dpi, is several micrometers, so that the two identical pixels are no longer positioned in the same space, and the pixel comparison becomes meaningless. Therefore, the area concept needs to be introduced here: respectively calculating total color values sum (C), sum (M), sum (Y) and sum (K) of color values of pixel points of the whole image according to four primary colors CYMK;

where m and n are the width and height of the image pixels (pixels), respectively, and sum (C) represents the sum of all cyan color values in one image; sum (M) represents the sum of the product color values; sum (Y) represents the sum of the yellow color values; sum (k) represents the sum of all black values in the image. And converting the total pixel value of each primary color into a primary color area ratio P on the image area:

P(C)＝sum(C)/m*n；

P(M)＝sum(M)/m*n；

P(Y)＝sum(Y)/m*n；

P(K)＝sum(K)/m*n；

based on the area ratios, it can be determined that if the picture area ratios P (C), P (M), P (Y), and P (K) of two identical image contents are the same, the two images are identical in color and have no color difference. If the area ratio is different, the image has colors, and the larger the difference is, the larger the color difference is.

The comparison of the pixel total color values within the total area to the size of the color value area ratio per unit area is because, however, the comparison of the total color values of the total pixel primaries is not comparable: different total color values of images may differ by several times or several tens of times, and the difference of the total color values of a certain primary color may be known to have a color difference, but the size of the color difference corresponding to the difference is not comparable, for example, the total color value 10000 of C color of an A1 image, 10100 of C color of an A2 image, 100 of A1 and A2 color values, 100000 of C color of another B1 image, 100100 of C color value of a B2 image, and 100 of B1 and B2 total color values, obviously, the actual size of the color difference of two images, which are both 100 of color values, may differ by 10 times. Therefore, in the above process, the total color value of each primary color of the total pixels under the total area is converted into the primary color coverage area ratio P, and the value of P can be seen from the formula to be in the range of 0-100, so that the color difference described by the coverage ratio difference is more universal and comparable.

In one embodiment, as shown in FIG. 2, step 300: calculating the color coverage rate of each first primary color image and the color coverage rate of each second primary color image, which specifically comprises the following steps: for any one of the first primary color images, the first primary color image is divided into a plurality of first primary color regions, that is, step 301: and dividing an image area. Then, step 302 is performed: calculating the regional color value, namely calculating the color value of each first primary color region; then, step 303 is performed: calculating the color coverage rate, namely determining the average value of the color values of all the first primary color areas as the color coverage rate of the first primary color image; taking four first primary color images as an example, calculating the color value of each first primary color region specifically includes the following steps:

m(f)＝m/f

wherein m (f) is the image width of each region, m is the width of the image to be compared, n is the height of the image to be compared, f is the number of regions for dividing the image to be compared, i is any pixel point on the region image width, j is any pixel point on the region image height, and sum () is the sum of color values corresponding to each primary color of each region;

the calculating the color coverage of the first primary color image specifically comprises:

P(f)＝sum(f)/m(f)*n；

wherein P (f) is the color value coverage of each primary color in each partition.

In addition, for any one of the second primary color images, the second primary color image is divided into a plurality of second primary color regions, the color value of each second primary color region is calculated, and the average value of the color values of all the second primary color regions is determined as the color coverage of the second primary color image. The specific operation steps of the process and the operation of calculating the color value of each first primary color region are the same as the operation steps of calculating the color coverage of the first primary color image, and a repeated description thereof will not be provided.

In one embodiment, as shown in FIG. 2, step 400: comparing the color coverage rate of the first primary color image with the color coverage rate of the corresponding second primary color image to obtain the color difference value of each second primary color image specifically comprises: and the color coverage rate of the first primary color image is different from the color coverage rate of the corresponding second primary color image, so that the color difference value of each second primary color image is obtained. That is, two images a and B, i.e., the target image and the printed image of the target image, are subtracted from each other to obtain the color value coverage ratio P (f) of each partition, and the obtained difference is the color difference value between the two images based on the primary colors, and then step 600 is performed: and correcting the image according to the color difference value, and correcting the color difference value of each partition of each primary color to enable the colors of the two images to be consistent.

In practical application, for example, two photos can be seen by naked eyes that two pictures with the same content have obvious color difference, but no instrument is used for measuring and obtaining data color difference description, the requirement of comparing the color difference between the two pictures with the same content is necessary in reality, and in the traditional printing field, at present, a data image color difference description mode still does not exist, so that the problem is solved, the production process of a printing machine can be automatically controlled in a closed loop mode, and a method for quantitatively describing the image color difference is firstly solved. The invention provides a digital image color difference comparison method, a quantitative calculation method for image color difference and a product adopting the quantitative image color description method for automatic closed-loop control of printer color. Specific method implementation steps can also be shown as follows, but the implementation sequence is not limited to the steps, and the following step sequence is only used for reference.

The method comprises the following steps: the images to be compared can be acquired by a digital camera or a scanner.

Step two: the acquired digital images are adjusted in resolution in the computer, here 72dpi, a moderate resolution, to obtain a balance in accuracy and processing speed.

Step three: the resolution-adjusted image is converted into a color space, usually RGB to CMYK, where a color profile ICC color separation is used, and two contrast images must be kept separated by the same color profile during the two contrast images.

Step four: and dividing image regions, wherein in order to avoid errors caused by different local image area rates, the image needing to be compared can be divided into f regions to obtain 1-f regions.

Step five: the area coverage of the pixel color values is calculated by primary color and by region. And then subtracting the color value coverage rate P (f) obtained by each base color and each subarea obtained by the two images, wherein the obtained difference is the color difference value between the two images based on the base colors, and the color difference value of each subarea of each base color is respectively corrected to enable the colors of the two images to be consistent.

Based on the method for calculating the image color difference provided by the invention, the method can be used in the color closed-loop control of the traditional sheet-fed offset press, the reference sample sheet for printing reference, namely the target image is taken as a target value, and the image product actually printed by the press is taken as a result value.

In the traditional printing process, a feedback system is that human eyes collect a result value, the result value is compared with a target value and then a printer system is adjusted through a human brain, and the result value is the same as the target value after being repeated for several times. Digital cameras can be used for digital acquisition of the target values and the result values; the feedback system and the comparison process both adopt the technical method as follows: and (3) storing the collected image in a color separation and partition manner, contrasting the color value coverage rate according to the primary colors according to the areas to obtain the color difference of the color value coverage rate, and correcting the size of the printing ink of the printing machine.

As shown in fig. 3, the present invention further provides a system for calculating chromatic aberration of an image, the system comprising: an image acquisition module 201, an image conversion module 203, a color coverage calculation module 204 and a color difference calculation module 205.

The image acquisition module 201 is configured to acquire a target image and a print image of the target image, and acquire an image to be compared by using a digital camera or a scanner; the image conversion module 203 is configured to perform color space conversion on the target image to obtain at least one first primary color image, and perform color space conversion on the print image to obtain at least one second primary color image; a first primary color image corresponds to a second primary color image; the first primary color image and the second primary color image are both images in a printing color mode; the color coverage ratio calculating module 204 is used for calculating the color coverage ratio of each first primary color image and the color coverage ratio of each second primary color image; the color difference calculating module 205 is configured to compare the color coverage of the first primary color image with the color coverage of the corresponding second primary color image, so as to obtain a color difference value of each second primary color image.

In one embodiment, as shown in fig. 3, the system further comprises: an image modification module 206; the image correction module 206 is configured to correct the corresponding second primary color image according to the color difference value.

In one embodiment, as shown in fig. 3, the system further comprises: a resolution adjustment module 202; the resolution adjustment module 202 is configured to adjust the resolution of the target image and the resolution of the print image to a set resolution value to achieve a balance between accuracy and processing speed.

In one embodiment, as shown in fig. 3, the color coverage calculation module 204 includes: a first calculation submodule 209 and a second calculation submodule 207; the first calculating submodule 209 is configured to, for any one of the first primary color images, divide the first primary color image into a plurality of first primary color regions, calculate color values of the first primary color regions, and determine an average value of the color values of all the first primary color regions as a color coverage of the first primary color image; the second calculating submodule 207 is configured to, for any one of the second primary color images, divide the second primary color image into a plurality of second primary color regions, calculate color values of the respective second primary color regions, and determine an average value of the color values of all the second primary color regions as a color coverage of the second primary color image.

In an embodiment, as shown in fig. 3, the color difference calculation module 205 specifically includes a third calculation sub-module 208; the third calculating sub-module 208 is configured to perform a difference between the color coverage of the first primary color image and the color coverage of the corresponding second primary color image, so as to obtain a color difference value of each second primary color image.

In the prior art, a printing machine based on closed-loop color adjustment controlled by a computer exists, but the color difference comparison modes of the implementation modes are different. In addition, a method for judging image color difference based on image pixel color does not exist at present.

The current single-sheet offset printing machines all adopt a scheme of manually adjusting colors, namely, human eyes distinguish the color difference between a sample sheet and a printed matter, human brains judge the color difference of each area of each primary color, and then the given amount of ink of each area of each primary color of the printing machines is manually corrected to continuously correct the difference of the color difference between the printed product and the sample manuscript. Undoubtedly, the efficiency of the process depends on the level of judging the color difference by operators, the time for operators with rich experience is short, the quality is good, the quality and the production efficiency of products completely depend on the level of the operators, and the personnel dependence is extremely high.

The invention can make the color correction of the whole printing machine independent of human, once the quantitative judgment method of color difference is provided, the quantized value of color difference can be used for manufacturing the product described above by using a computer calculation mode according to the quantized value, so that the color correction of the printing machine can be automated, the dependence of human is eliminated, and the production efficiency and the product quality can be greatly improved.

The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other. For the system disclosed by the embodiment, the description is relatively simple because the system corresponds to the method disclosed by the embodiment, and the relevant points can be referred to the method part for description.

The principle and the embodiment of the present invention are explained by applying specific examples, and the above description of the embodiments is only used to help understanding the method and the core idea of the present invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, the specific embodiments and the application range may be changed. In view of the above, the present disclosure should not be construed as limiting the invention.

Claims (10)

1. A method of calculating image color differences, the method comprising:

acquiring a target image and a printing image of the target image;

performing color space conversion on the target image to obtain at least one first primary color image, and performing color space conversion on the printing image to obtain at least one second primary color image; one said first primary color image corresponding to one said second primary color image; the first primary color image and the second primary color image are both images in a printed color mode;

calculating the color coverage rate of each first primary color image and the color coverage rate of each second primary color image;

and comparing the color coverage rate of the first primary color image with the corresponding color coverage rate of the second primary color image to obtain the color difference value of each second primary color image.

2. The method according to claim 1, further comprising, after comparing the color coverage of the first primary color image with the color coverage of the corresponding second primary color image to obtain the color difference value of each second primary color image:

and correcting the corresponding second primary color image according to the color difference value.

3. The method of claim 1, wherein before the color-space converting the target image to obtain at least one first primary color image and the color-space converting the print image to obtain at least one second primary color image, the method further comprises:

adjusting the resolution of the target image and the resolution of the printed image to a set resolution value.

4. The method according to claim 1, wherein the calculating the color coverage of each of the first primary color images and the color coverage of each of the second primary color images specifically comprises:

for any one first primary color image, dividing the first primary color image into a plurality of first primary color areas, calculating the color value of each first primary color area, and determining the average value of the color values of all the first primary color areas as the color coverage rate of the first primary color image;

for any one second primary color image, dividing the second primary color image into a plurality of second primary color areas, calculating the color value of each second primary color area, and determining the average value of the color values of all the second primary color areas as the color coverage rate of the second primary color image.

5. The method according to claim 1, wherein the comparing the color coverage of the first primary color image with the color coverage of the corresponding second primary color image to obtain the color difference value of each second primary color image comprises:

and the color coverage rate of the first primary color image is different from the color coverage rate of the corresponding second primary color image, so that the color difference value of each second primary color image is obtained.

6. A system for calculating image color differences, comprising:

the image acquisition module is used for acquiring a target image and a printing image of the target image;

the image conversion module is used for performing color space conversion on the target image to obtain at least one first primary color image, and performing color space conversion on the printing image to obtain at least one second primary color image; one said first primary color image corresponding to one said second primary color image; the first primary color image and the second primary color image are both images in a printed color mode;

the color coverage rate calculation module is used for calculating the color coverage rate of each first primary color image and the color coverage rate of each second primary color image;

and the color difference calculating module is used for comparing the color coverage rate of the first primary color image with the color coverage rate of the corresponding second primary color image to obtain the color difference value of each second primary color image.

7. The system for calculating chromatic aberration of an image according to claim 6, further comprising:

and the image correction module is used for correcting the corresponding second primary color image according to the color difference value.

8. The system for calculating chromatic aberration of an image according to claim 6, further comprising:

and the resolution adjusting module is used for adjusting the resolution of the target image and the resolution of the printing image to a set resolution value.

9. The system of claim 6, wherein the color coverage calculation module comprises:

the first calculation sub-module is used for dividing the first primary color image into a plurality of first primary color areas for any one first primary color image, calculating the color value of each first primary color area, and determining the average value of the color values of all the first primary color areas as the color coverage rate of the first primary color image;

and the second calculation submodule is used for dividing the second primary color image into a plurality of second primary color areas for any one second primary color image, calculating the color value of each second primary color area, and determining the average value of the color values of all the second primary color areas as the color coverage rate of the second primary color image.

10. The system for calculating an image color difference according to claim 6, wherein the color difference calculating module specifically comprises:

and the third calculating submodule is used for subtracting the color coverage rate of the first primary color image from the corresponding color coverage rate of the second primary color image to obtain the color difference value of each second primary color image.

Images