CN109886902B - Printing plate making color separation method of black and white image based on three-color black - Google Patents

Abstract

The invention discloses a printing plate-making color separation method based on three-color black black and white images. First, the image is converted into a grayscale image; then the obtained grayscale image is adjusted three times to obtain three color separation black plate images. Then, the obtained three different color separation black plate images are fused; finally, the fused image is plate-making and printing. The black version is superimposed on each other, so as to achieve the improvement of the black and white picture effect.

Description

A printing plate-making color separation method based on three-color black black and white images

technical field

The invention belongs to the technical field of printing, and relates to a printing plate-making color separation method based on black-and-white images of three-color black.

Background technique

Black and white images are more and more favored by photographers because of their unique appeal, elegance, purity, and delicate layering. At the same time, photographers have the need to print black and white photographic works.

There are usually two ways to print black and white images: one is monochrome black printing, that is, black ink is used alone. This process method is simple and low in cost, but because the density of black ink is about 1.6, the level reproduction is not good. It cannot accurately reflect the photographer's intention; the other is to print black and white images in four colors, that is, cyan (C), magenta (M), yellow (Y), and black (K) are overprinted in four colors. The method can improve the printing contrast and increase the image level, but because the human eye is most sensitive to achromatic gray, a slight deviation of the C, Y, and M inks during the printing process will cause color casts, which will have a greater visual impact, and overprinting will occur. High difficulty.

Therefore, in order to carry out a high-level, high-efficiency and simple way of printing black and white images, a new printing process must be found.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a color separation method for printing plate-making based on three-color black black and white images, which solves the problem of impure black and white colors caused by the existing printing technology.

The technical scheme adopted in the present invention is a color separation method for printing plate-making based on black and white images of three-color black, and the specific steps are as follows:

Step 1, convert the image to a grayscale image;

In step 2, the grayscale image obtained in step 1 is subjected to three-time tone adjustment to obtain three color-separated black version images;

Step 3, fuse the three different color-separated black version images obtained in step 2;

In step 4, the image fused in step 3 is subjected to plate making and printing.

The feature of the present invention also lies in:

The step 1 is specifically: convert the image to grayscale according to formula (1) to obtain a grayscale image:

Gray=(0.2973·R ^2.2 +0.6274·G ^2.2 +0.0753·B ^2.2 ) ^1/2.2 (1)

Among them, R, G, B represent the value of each channel of the color image; Gray represents the pixel value of the converted grayscale image;

Wherein step 2 specifically includes:

Step 2.1, adjust the tone of the grayscale image obtained in step 1 by formula (2) to obtain the first color separation black image:

Among them, x represents the pixel value of the grayscale image, y represents the pixel value of the transformed image, x ₁ and y ₂ represent the coordinates of the point of the first color separation black version curve, and x ₁ ranges from 5% to 30%. The range of y ₂ is 70% to 100%;

Step 2.2, adjust the tone of the image obtained in step 1 by formula (2) again to obtain the second color separation black image:

The range of x ₁ is 60% to 85%, and the range of y ₂ is 20% to 40%;

In step 2.3, the grayscale image obtained in step 1 is adjusted by formula (3) to obtain the third color separation black image:

Wherein x ₁ , y ₁ , x ₂ , y ₂ represent the coordinates of the points of the third dichroic black version curve, where x ₁ ranges from 0% to 15%, y ₁ ranges from 10% to 30%, x ₂ The range of 85% to 100%, y ₂ and y ₁ are the same.

The step 3 is specifically to fuse the first, second, and third black color-separated images through drawing software to obtain a fused three-color black image.

The beneficial effects of the present invention are:

The color separation method for printing plate-making based on three-color black black and white images of the present invention can make black more accurate and pure, without noise and color cast, avoid the problem of impure black and white colors caused by traditional printing, and maintain the image quality. The details and layers are richer, and the printing quality is more stable; in general, the effect of black and white images is improved, and the expressiveness of black and white images is improved.

Description of drawings

1 is a first and second black plate tone adjustment curves in a printing plate-making color separation method based on three-color black black and white images of the present invention;

2 is a third black plate tone adjustment curve in a printing plate-making color separation method based on three-color black black and white images of the present invention;

Fig. 3 is a kind of black-and-white manuscript drawing to be printed in the printing plate-making color separation method based on the black-and-white image of three-color black of the present invention;

4 is a comparison diagram of the black and white image effect of conventional monochrome black printing in a printing plate-making color separation method based on three-color black black and white images of the present invention;

FIG. 5 is a black-and-white image effect diagram of three-color black printing based on a three-color black-based black-and-white image printing plate-making color separation method of the present invention.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

The invention provides a color separation method for printing plate-making based on black and white images of three-color black, and the specific steps are as follows:

Step 1, convert the image into a grayscale image: Step 1 is specifically: performing grayscale conversion on the image according to formula (1) to obtain a grayscale image:

Gray=(0.2973·R ^2.2 +0.6274·G ^2.2 +0.0753·B ^2.2 ) ^1/2.2 (1)

Among them, R, G, B represent the value of each channel of the color image; Gray represents the pixel value of the converted grayscale image.

In step 2, the grayscale image obtained in step 1 is adjusted three times to obtain three color-separated black images:

Step 2.1, adjust the tone of the grayscale image obtained in step 1 by formula (2) to obtain the first color separation black image:

Among them, x represents the pixel value of the grayscale image, and y represents the pixel value of the transformed image. As shown in Figure 1, x ₁ and y ₂ represent the coordinates of the point of the first color separation curve, and x ₁ is in the pixel range 5 %～30%, y ₂ is in the pixel range 70%～100%;

Step 2.2, adjust the tone of the image obtained in step 1 by formula (2) again to obtain the second color separation black image:

Among them, x ₁ is in the range of 60% to 85% of the pixel range, and y ₂ is in the range of 20% to 40% of the pixel range;

In step 2.3, the grayscale image obtained in step 1 is adjusted by formula (3) to obtain the third color separation black image:

Wherein x ₁ , y ₁ , x ₂ , y ₂ represent the coordinates of the points of the third dichroic black version curve, where x ₁ is in the pixel range 0%-15%, y ₁ is in the pixel range 10%-30%, x ₂ In the pixel range of 85% to 100%, y ₂ and y ₁ are the same. According to FIG. 2 , in general, y ₂ and y ₁ are the same, but according to different needs or image characteristics, y ₂ and y ₁ may be different.

Step 3, fuse the three different color-separated black version images obtained in step 2;

In step 4, the image fused in step 3 is subjected to plate making and printing.

The advantages of the present invention are explained using the principle of operation:

Step 1, convert the color image into a grayscale image, and the conversion method is shown in the following formula to obtain a grayscale image.

Gray=(0.2973·R ^2.2 +0.6274·G ^2.2 +0.0753·B ^2.2 ) ^1/2.2 (1)

In step 2, the grayscale image obtained in step 1 is subjected to three-time tone adjustment to obtain three color-separated black version images;

Step 2.1, adjust the tone of the grayscale image according to the following formula to obtain the first black version color separation image.

In step 2.2, the grayscale image is adjusted according to the following formula to obtain the second black color separation image.

In step 2.3, the grayscale image is adjusted according to the following formula to obtain the third black color separation image.

The value range of the obtained first, second, and third black color separation images is the same as that of the original RGB image: 0 to 255. To convert them to 0 to 100, convert them according to the following formula:

y=100-x/255*100 (7)

Among them, x represents the pixel value of the first, second, and third black color separation images; y represents the value after the pixel is converted to 0 to 100;

Step 3. Create a blank image with the same size and resolution as the primary color image in Photoshop, Illustrator, CorelDRAW and other graphics software. The color mode must be CMYK, and the file format can be tiff. The color image is copied into the three channels of the new image, such as C, Y, and K channels, and the M channel is kept as 0 to obtain a three-color black image after fusion.

Step 4, plate making and printing: plate making and printing the fused three-color black image according to a conventional printing process to obtain a printed black and white image that meets the requirements.

The present invention is a method for printing black and white images by printing black ink three times. The files generated by this method are tif format files in CMYK mode, which are the same as conventional printing files, and can be directly used for phototypesetting output or CTP version directly. The output process and The equipment can directly use the original equipment. In printing, in conventional printing companies, four-color and above printing machines are used to print color prints. Four color inks of CMYK are applied to the four units respectively. When printing with conventional equipment, it is only necessary to apply black ink on all three units, and only one unit is required to run off pressure and idle, and it is not necessary for the existing printing enterprises to update the printing equipment. . This method has good feasibility.

As shown in Figure 3 is the black and white manuscript to be printed. After conventional monochromatic black plate making and printing, the obtained effect figure is shown in Figure 4 as the black and white image effect of conventional monochromatic black printing. As can be seen from the figure, The effect of monochrome black printing has small contrast and low customer acceptance. The black and white image effect after plate making and printing using the method of the present invention is shown in Figure 5, which effectively increases the contrast, and the effect is obvious, highlighting the characteristics of black and white images , the customer has a high degree of recognition.

Claims (3)

1. a printing plate-making color separation method based on the black and white image of three-color black, is characterized in that, concrete steps are as follows: Step 1, convert the image to a grayscale image; In step 2, the grayscale image obtained in step 1 is subjected to three-time tone adjustment to obtain three color-separated black images, as follows: Step 2.1, adjust the tone of the grayscale image obtained in step 1 by formula (2) to obtain the first color separation black image:

Among them, x represents the pixel value of the grayscale image, y represents the pixel value of the transformed image, x ₁ and y ₂ represent the coordinates of the point of the first color separation black version curve, and x ₁ is in the pixel range of 5% to 30%, y ₂ is 70% to 100% in the pixel range; Step 2.2, adjust the tone of the image obtained in step 1 by formula (2) again to obtain the second color separation black image: Among them, x ₁ is in the range of 60% to 85% of the pixel range, and y ₂ is in the range of 20% to 40% of the pixel range; In step 2.3, the grayscale image obtained in step 1 is adjusted by formula (3) to obtain the third color separation black image:

Wherein x ₁ , y ₁ , x ₂ , y ₂ represent the coordinates of the points of the third dichroic black version curve, where x ₁ is in the pixel range 0%-15%, y ₁ is in the pixel range 10%-30%, x ₂ In the pixel range 85% to 100%, y ₂ and y ₁ are the same; Step 3, fuse the three different color-separated black version images obtained in step 2; In step 4, the image fused in step 3 is subjected to plate making and printing. 2. a kind of printing plate-making color separation method based on the black-and-white image of three-color black according to claim 1, is characterized in that, described step 1 is specifically: carry out grayscale conversion by the image according to formula (1), obtain grayscale Degree image: Gray=(0.2973·R ^2.2 +0.6274·G ^2.2 +0.0753·B ^2.2 ) ^1/2.2 (1) Among them, R, G, B represent the value of each channel of the color image; Gray represents the pixel value of the converted grayscale image. 3. a kind of printing plate-making color separation method based on the black and white image of three-color black according to claim 1, is characterized in that, described step 3 is specifically to pass the first, second, third black plate color separation image through The drawing software is used for fusion to obtain a fused three-color black image.

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