CN109886902B - Printing plate making color separation method of black and white image based on three-color black - Google Patents
Printing plate making color separation method of black and white image based on three-color black Download PDFInfo
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- CN109886902B CN109886902B CN201910054924.2A CN201910054924A CN109886902B CN 109886902 B CN109886902 B CN 109886902B CN 201910054924 A CN201910054924 A CN 201910054924A CN 109886902 B CN109886902 B CN 109886902B
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Abstract
The invention discloses a printing plate making color separation method based on a black-and-white image of three-color black, which comprises the steps of firstly converting the image into a gray image; thirdly, carrying out third-time tone adjustment on the obtained gray level image to obtain three color separation black images; then fusing the obtained three different color separation black images; and finally, carrying out plate making and printing on the fused image, wherein the invention adopts a three-time monochromatic black printing method with different dosage, and realizes the improvement of black and white picture effect by setting three black plates with different gradation levels and mutually overlapping.
Description
Technical Field
The invention belongs to the technical field of printing, and relates to a printing plate making color separation method based on a black-and-white image of three-color black.
Background
Black and white images are more and more popular with photographers because of their unique infectivity and their elegant, pure, and fine layering. At the same time, photographers have a need to print black and white photographic works.
There are generally two methods of printing black and white images: the process method is simple and low in cost, but the density of the black ink is about 1.6, the level reappearance is not good, and the intention of a photographer cannot be accurately reflected; the other is a black-and-white image printed in four colors, namely, the black (C), the magenta (M), the yellow (Y) and the black (K) are overprinted, the printing mode can improve the printing contrast and increase the image level, but because human eyes are most sensitive to achromatic gray, the C, Y and M printing ink slightly deviates in the printing process, color cast occurs, the visual effect is large, and the overprinting difficulty is large.
Therefore, a new printing process is required to perform high-level, high-efficiency, and simple printing of black-and-white images.
Disclosure of Invention
The invention aims to provide a printing plate making and color separation method of a black-and-white image based on three-color black, which solves the problem of the existing printing technology that the black and white color is not pure.
The invention adopts the technical scheme that a three-color black-based printing plate making and color separation method for black and white images comprises the following specific steps:
step 1, converting an image into a gray image;
step 2, carrying out third-time tone adjustment on the gray level image obtained in the step 1 to obtain three color separation black images;
step 3, fusing the three different color separation black images obtained in the step 2;
and 4, carrying out plate making and printing on the image fused in the step 3.
The invention is also characterized in that:
wherein the step 1 specifically comprises the following steps: carrying out gray level conversion on the image according to the formula (1) to obtain a gray level image:
Gray＝(0.2973·R 2.2 +0.6274·G 2.2 +0.0753·B 2.2 ) 1/2.2 (1)
wherein, R, G, B represent the value of each channel of the color image; gray represents the pixel value of the converted Gray level image;
wherein the step 2 specifically comprises:
step 2.1, carrying out tone adjustment on the gray level image obtained in the step 1 through an equation (2) to obtain a first color separation black domain image:
wherein x represents a pixel value of a gray-scale image, y represents a pixel value of a transformed image, x 1 、y 2 Coordinates of points, x, representing the curve of the first dichroic black 1 In the range of 5% to 30%, y 2 The range of (A) is 70-100%;
step 2.2, adjusting the tone of the image obtained in the step 1 again through the formula (2) to obtain a second dichroic black area image:
wherein x 1 In the range of 60% to 85%, y 2 The range of (1) is 20-40%;
step 2.3, performing tone adjustment on the gray level image obtained in the step 1 through a formula (3) to obtain a third color separation black area image:
wherein x is 1 、y 1 、x 2 、y 2 Coordinates of points representing the third color separation black curve, wherein x 1 In the range of 0% to 15%, y 1 In the range of 10% to 30%, x 2 In the range of 85% to 100%, y 2 And y 1 The same is true.
And 3, fusing the first, second and third black color separation images through drawing software to obtain a fused three-color black image.
The beneficial effects of the invention are:
the printing plate making and color separation method based on the black-white image of the three-color black can ensure that the black is more accurate and pure, has no color mixing and color cast, avoids the problem of the unreal black-white color caused by the traditional printing, maintains the details of the image, has richer layers and more stable printing quality; in general, the black-and-white image effect is improved, and the expressive force of the black-and-white image is improved.
Drawings
FIG. 1 is a first and second black tone adjustment curves of a method for separating a black-and-white image from a three-color black-based plate for plate-making according to the present invention;
FIG. 2 is a third black tone adjustment curve of the present invention for a black-and-white image-based method for platemaking and color separation;
FIG. 3 is a black and white manuscript image to be printed in the plate-making and color-separating method for printing black and white images based on three-color black of the present invention;
FIG. 4 is a comparison chart of the black and white image effect of conventional monochrome black printing in a plate-making and color-separation method for a monochrome image based on three-color black according to the present invention;
fig. 5 is a black-and-white image effect diagram of the three-color black printing of the printing plate making color separation method based on the three-color black-and-white image of the present invention.
Detailed Description
The invention is described in detail below with reference to the drawings and the detailed description.
The invention provides a printing plate making color separation method based on a black-and-white image of three-color black, which comprises the following specific steps:
step 1, converting an image into a gray image: the step 1 specifically comprises the following steps: carrying out gray level conversion on the image according to the formula (1) to obtain a gray level image:
Gray＝(0.2973·R 2.2 +0.6274·G 2.2 +0.0753·B 2.2 ) 1/2.2 (1)
wherein, R, G, B represent the value of each channel of the color image; gray denotes a pixel value of the converted Gray image.
Step 2, performing third-time tone adjustment on the gray level image obtained in the step 1 to obtain three color separation black images:
step 2.1, performing tone adjustment on the gray level image obtained in the step 1 through an equation (2) to obtain a first color separation black area image:
where x represents the pixel value of the grayscale image and y represents the pixel value of the transformed image, x being shown in FIG. 1 1 、y 2 Represents the firstCoordinates of points of the color separation black curve, x 1 In the pixel range of 5% -30%, y 2 70% -100% of the pixel range;
step 2.2, adjusting the tone of the image obtained in the step 1 again through an equation (2) to obtain a second dichroic black area image:
wherein x is 1 In the pixel range of 60% -85%, y 2 In the pixel range of 20% -40%;
step 2.3, performing tone adjustment on the gray level image obtained in the step 1 through a formula (3) to obtain a third color separation black area image:
wherein x 1 、y 1 、x 2 、y 2 Coordinates of points representing the third color separation black curve, wherein x 1 In the pixel range of 0% -15%, y 1 10% -30% of pixel range, x 2 In the pixel range of 85% -100%, y 2 And y 1 Similarly, according to FIG. 2, in general, y 2 And y 1 Same, according to different needs, or image characteristics, y 2 And y 1 May not be the same.
Step 3, fusing the three different color separation black images obtained in the step 2;
and 4, carrying out plate making and printing on the image fused in the step 3.
The advantages of the invention are explained by using the principle of operation:
step 1, converting the color image into a gray mode image, wherein the conversion mode is shown as the following formula, and the gray image is obtained.
Gray＝(0.2973·R 2.2 +0.6274·G 2.2 +0.0753·B 2.2 ) 1/2.2 (1)
Step 2, performing third-time tone adjustment on the gray level image obtained in the step 1 to obtain three color separation black images;
and 2.1, carrying out tone adjustment on the gray level image according to the following formula to obtain a first black color separation image.
And 2.2, carrying out tone adjustment on the gray level image according to the following formula to obtain a second black color separation image.
And 2.3, carrying out tone adjustment on the gray level image according to the following formula to obtain a third black color separation image.
The obtained first, second and third black color separation image numerical ranges are the same as the original RGB image numerical range: 0 to 255, which is converted to 0 to 100 according to the following formula:
y＝100-x/255*100 (7)
wherein, x represents the pixel values of the first, the second and the third black plate color separation images; y represents a value after the pixel is converted to 0 to 100;
and 3, establishing blank images with the same size and resolution as the primary color images in graphics software such as Photoshop, illustrator, corelDRAW and the like, copying the first, second and third black color separation images into three channels of a newly-created image, such as C, Y and K channels, respectively, and keeping the M channel to be 0 to obtain the fused three-color black image, wherein the color mode must be CMYK and the file format can be tiff.
And 4, plate making and printing: and (4) carrying out plate making and printing on the fused three-color black image according to a conventional printing process to obtain a black-and-white image meeting the requirement.
The invention is a method for printing black and white image by printing black ink for three times, the file generated by the method is a tif format file in CMYK mode, is the same as the file printed conventionally, can be directly used for typesetting and outputting or directly outputting CTP plate, and the output process and equipment can be directly realized by the original equipment. In the printing, in conventional printing enterprises, multi-purpose four-color and above printing machines print colorful printed matters, the colors of the four-color printing are cyan (C), magenta (M), yellow (Y) and black (K), namely, four units respectively print ink of four colors of CMYK, when conventional equipment is used for printing, only three units are required to be respectively coated with black ink, and only one unit is required to leave a pressure idle running, and the printing equipment of the conventional printing enterprises is not required to be updated. The method has good feasibility.
As shown in fig. 3, the black-and-white manuscript picture to be printed is subjected to plate making and printing of conventional monochromatic black, and the obtained effect picture is as shown in the black-and-white image effect of the conventional monochromatic black printing of fig. 4, and as can be seen from the picture, the contrast of the effect of the monochromatic black printing is small, and the customer acceptance is low, and the effect of the black-and-white image after the plate making and printing by using the method of the invention is as shown in fig. 5, so that the contrast is effectively enlarged, the effect is obvious, the characteristics of the black-and-white image are highlighted, and the customer acceptance is high.
Claims (3)
1. A plate making and color separation method for black and white images based on three-color black is characterized by comprising the following specific steps:
step 1, converting an image into a gray image;
step 2, performing third-time tone adjustment on the gray level image obtained in the step 1 to obtain three color separation black images, which are specifically as follows:
step 2.1, performing tone adjustment on the gray level image obtained in the step 1 through an equation (2) to obtain a first color separation black area image:
wherein x represents a pixel value of a gray-scale image, y represents a pixel value of a transformed image, x 1 、y 2 Coordinates of points, x, representing the curve of the first dichroic black 1 In the pixel range of 5% -30%, y 2 Image onThe element range is 70-100%;
step 2.2, adjusting the tone of the image obtained in the step 1 again through the formula (2) to obtain a second dichroic black area image:
wherein x 1 In the pixel range of 60% -85%, y 2 In the pixel range of 20% -40%;
step 2.3, performing tone adjustment on the gray level image obtained in the step 1 through a formula (3) to obtain a third color separation black area image:
wherein x 1 、y 1 、x 2 、y 2 Coordinates of points representing the third color separation black curve, wherein x 1 In the pixel range of 0% -15%, y 1 In the pixel range of 10% -30%, x 2 In the pixel range of 85% -100%, y 2 And y 1 The same;
step 3, fusing the three different color separation black images obtained in the step 2;
and 4, carrying out plate making and printing on the image fused in the step 3.
2. The method according to claim 1, wherein the step 1 is specifically as follows: carrying out gray level conversion on the image according to the formula (1) to obtain a gray level image:
Gray＝(0.2973·R 2.2 +0.6274·G 2.2 +0.0753·B 2.2 ) 1/2.2 (1)
wherein, R, G, B represent the value of each channel of the color image; gray represents a pixel value of the converted Gray image.
3. The method according to claim 1, wherein step 3 is to fuse the first, second, and third black color separation images with a drawing software to obtain a fused three-color black image.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103171316A (en) * | 2012-11-16 | 2013-06-26 | 北京雅昌彩色印刷有限公司 | Black grey four-color offset printing technology |
| CN105262930A (en) * | 2015-10-20 | 2016-01-20 | 北京圣彩虹文化艺术发展股份有限公司 | ICC file manufacturing method of converting RGB color mode to CMYK color mode |
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| KR100484146B1 (en) * | 2002-07-06 | 2005-04-18 | 삼성전자주식회사 | Method for adjusting process black and driver there of |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN103171316A (en) * | 2012-11-16 | 2013-06-26 | 北京雅昌彩色印刷有限公司 | Black grey four-color offset printing technology |
| CN105262930A (en) * | 2015-10-20 | 2016-01-20 | 北京圣彩虹文化艺术发展股份有限公司 | ICC file manufacturing method of converting RGB color mode to CMYK color mode |
Non-Patent Citations (2)
| Title |
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| Photoshop中UCR与GCR分色参数设置及应用;楚高利等;《广东印刷》;20171020(第05期);全文 * |
| 彩色复制中黑版阶调的设定方法;陆亚萍;《广东印刷》;20141220(第06期);全文 * |
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