How to control the prepress quality of character p

How to control the prepress quality of character pictures (graphics and text)

in printed matter, character pictures not only account for a certain proportion, but also are often the visual center of printed matter. Therefore, the prepress quality control of figure pictures is a key link that cannot be ignored in the printing process

I. step adjustment of hair and dark clothes

hair and dark clothes are the parts of these production presses that are prone to problems in printing and reproduction. In many magazines, picture albums, packaging and other printed materials, the common quality problems of people's pictures are the improper control of the gradation of hair and dark clothes. First, the black pictures such as hair are lack of hierarchy, or even level; Second, the dark color of hair and dark clothes is turbid and the color is not pure

analyze the reason, and the problem lies in the control of image quality by the prepress adjustment personnel. Our current image quality control often relies on Photoshop software. The image adjustment personnel also rely on the perception of the Photoshop interface to judge the image quality. As a result, dark hair and dark clothes appear to have tone changes on the computer monitor, but when printed on paper, these tone changes are damaged or even disappear completely due to insufficient ink density and increased printing points. Therefore, we should adapt to the sensory differences between the two media, and we should not set the levels of hair and dark clothes in the figure pictures too deep. Use Photoshop's straw tool to check the C, y, m, K values of hair and dark clothes. If it is too deep, the following two methods can be used. Method 1: use the lasso tool to select the parts of hair and dark clothes, input a certain feather value, and then highlight the parts of hair and dark clothes through image/adjustment/color scale or image/adjustment/curve. Method 2: enter the highlight menu from the image/adjustment/dark tone/when exploring the new development path of plastic granulator technology, and call up the dark tone/high light dialog box. By increasing the value of the dialog box dark tone, you can improve the dark tone condition. The higher the value, the brighter the dark part becomes

when processing prepress pictures, first analyze and judge according to the environment and background of the picture. If it is neutral pure black, use straw tool to check the values of C, y, m and K. For the pictures used in offset printing process, the C, y, m and K values cannot all be high at the same time. The black version should be the main one. Appropriately increase the K value and reduce the C, y and m values to show black. Doing so, on the one hand, makes the dark tone more pure, on the other hand, avoids the lack of hierarchy caused by multi-color mixing. If it is a warm tone, let the values of Y and m be slightly higher, otherwise let the value of C be higher

Figure 1 shows the original picture. The black hair on it can see the tone changes on the computer monitor, but when printed on paper, these tone changes are likely to be damaged or even disappear completely. Therefore, pre press processing should pay special attention to these parts

Figure 1 original picture

Figure 2 image adjustment interface

as shown in Figure 2, use the lasso tool to select the parts of hair and dark clothes, and highlight the parts of hair through image/adjustment/color scale or image/adjustment/curve after eclosion, so as to prevent the damage of gradation or merging during printing

as shown in Figure 2, use the lasso tool to select the parts of hair and dark clothes, and brighten the hair parts through image/adjustment/color scale or image/adjustment/curve after feathering, so as to prevent the damage of scale or merging during printing

after adjustment, check the values of C, y, m and K with a straw tool to ensure that everything is safe, as shown in Figure 3. The maximum value of C, y, m and k points in offset printing process can be about 97%, and can not be set to 100%. The total ink volume is determined according to different background color synthesis methods, and the total amount of C, y, m and K is generally not more than 350%

Figure 3 picture information interface

II. Hierarchy adjustment of light colors such as skin and shirt

people's skin and light colored shirt are also parts that are prone to problems in printing. For example, if the highlight is too bright, there is an absolute difference on the printed matter, and then the color of bright color parts is not pure

most of the reasons are the quality problems of the original, but some are caused by inadequate pre press processing. The highlight part of many pictures has hierarchy and tone changes in Photoshop. It's also a little difficult to check it with straw tool. Why is it impossible to print it? Because a slight deviation in the printing plate will cause the loss of fine spots on the printing plate. Therefore, when adjusting the map, the highlight parts should be dimmed consciously. The method is the same as above. Use the lasso tool to select the parts of skin, shirt, etc., input a certain feather value, and then darken the parts of skin, shirt, etc. through image/adjustment/color scale or image/adjustment/curve. Or enter from the image/adjust/dim/highlight menu to call up the dim/highlight dialog box. By increasing the highlight value of the dialog box, you can improve the condition of skin, shirt, etc. If the image has moderate contrast, you can set the extremely high light area to about 3% when processing, and set the high light area of the required level to about 3% to avoid absolute

when processing people's pictures, the brightness should be adjusted in order to preserve the layers of skin and shirt highlights. Conventional brightness adjustment often causes color changes. To this end, we have explored a good method, first convert the picture mode to lab mode, and adjust the brightness on the lightness layer of lab mode, so that the brightness can be changed without causing color changes. Then switch the picture back to CYMK mode for printing

III. color adjustment of character pictures

people are particularly sensitive to the color feeling of the characters on the printed matter. If there is a slight deviation, they will detect the color deviation of the printed matter of the portrait, and the main reason why the original scene tone cannot be restored is (that is, the sample is constantly in the jaw, in the jaw, in the parallel segment or outside the gauge distance) that the amount of adjustment in the image processing is too large, the range is too large, and there is a lack of color management and monitoring of the whole printing process, just looking at the display, Adjust colors according to subjective feelings. The solution is:

(1) do a good job in color management and monitoring of the whole printing process, such as display calibration, so that the whole process has a reliable and stable color environment

(2) the adjustment amount of color should not be too large. First, in color adjustment, we should ensure the level of each color version, and do not cause the combination of tones and tone faults due to excessive color addition; The second is to maintain the normal proportion of color quantity and light quantity. When adjusting a certain color, we should maintain the relationship between light and shade, and we cannot only consider the bright part when adjusting the bright part, so that the middle and dark parts are unbalanced. Now some printing materials are exaggerated in color processing in pursuit of bright color, which loses the normal relationship of color and gives people a false feeling. This is actually a failure. If you want to adjust the color, you'd better turn the mode to lab mode and adjust it in the color channel of lab mode, so that the change of color will not affect the hierarchy. After adjustment, the color distribution of the whole or various color channels can be judged by the pixel distribution histogram

(3) master the change law of color, and improve the ability to judge color. Pay attention to the color relationship between objects. For example, the color of the light receiving surface is inseparable from the temperature change of the light source color, and the color of the backlight surface is closely related to the temperature change of the surrounding environment color. Therefore, when adjusting the color, we should master this color, but in the conditional stress-strain curve shown in Figure 1, it can not really reflect the change law of metal deformation strengthening, cold and warm, rather than simply deepening or brightening the solid color

for pictures with complex colors, we should focus on the control of the skin color of the characters, especially the skin color of the face. First of all, we should ensure that the skin is not red, yellow or blue. Even if the background is a little biased, customers and readers can accept it

IV. adjustment of image skin texture

due to the subject's own skin, or due to insufficient light, insufficient exposure, overexposure, too large light ratio, too hard light quality and other factors, the image skin texture is not ideal. However, if we can modify and improve the skin texture of the characters in these photos in prepress image processing, we can improve the image quality and customer satisfaction. It can be seen that some skills of moisturizing skin and beautifying portraits are the basic skills that map adjusters should have. When the operation is not time-consuming and does not affect the progress of work, try to deal with the texture of the skin as much as possible

there are many ways to beautify skin texture. The common method is blur method, that is, blur the skin with blur tool or filter/blur/Gauss blur menu to moisturize the skin. This trick is time-consuming to make, and a little careless processing will blur the contour of the portrait and affect the clarity of the photo. Now there are many software specially used to moisturize the skin, such as cleanskinfx neatimage, which is simple to operate and has good effect. Peers may wish to try it

there are always some small defects in the portrait pictures without special makeup and decoration. Although repairing these defects is not the work that our mapping personnel must complete, our customers always hope that the fewer such defects, the better. When adjusting the picture, beautify the skin by the way. It doesn't take much time, but the printing effect can be significantly improved. Why not