When rice is separated by GCR, black generation can be determined in Photoshop, and black generation controls the characteristics of the starting point and substitution amount of gray component substitution and the gray component substitution curve. This curve is not the final black version of the curve, but the grey component substitution curve. Photoshop presets four types of black curves, as shown in Figure 3, which are short-, medium-, long-, and full-scale black curves, and can use the Custom method, based on image neutrality. Gray, achromatic, and color levels determine the starting point, the amount of substitution, and the degree of change in the middle portion of the gray component. In Fig. 3a, the starting point of the slight gray substitution is 40% of the image tone. There is no substitute for the bright part of the image, the dark part of the tone is replaced, the replacement amount is less, and the black generation curve is steeper. CMY With a high content, this short tone black version is suitable for color-based manuscript production. In Fig. 3b, the starting point of the intermediate gray alternative is 20% of the image tone. At the same tone, the medium gray alternative has less CMY components than the light gray alternative, and the black version has a longer curve and is darker in the middle. The role of the tune area is obviously increased. This medium tone black edition is suitable for the production of medium and dark color originals. In Figure 3c, the starting point of heavy ash replacement is 10% of the image tone, the black version of the curve is flat, the amount of substitution is large, the CMY component is significantly reduced, and the black version plays a large role in the entire tone region of the image. The role of this long tone black version is suitable for the production of color-based, color-originated manuscripts. In Figure 3d, the starting point of the gray alternative is the 0 point of the image tone, the black version of the curve is a straight line of 45 degrees, and the gray component substitution amount reaches the maximum. This image of the full-scale blackened version is formed in the neutral gray. Does not contain CMY ingredients.
In addition, select Custom Options to open the Custom Black Edition dialog box, which is the black version generation dialog box. You can also manually determine the degree to which the black version replaces the CMY component. This is created for difficult-to-print, missing-color highlights (like snow-capped mountains) or dark-tone images (such as city nightscapes). This setting has a great influence on the color separation value of the image, and an incorrect curve will produce an uncorrectable color. Therefore, there are many factors to consider when selecting black curves or using custom curves.
(1) Images based on neutral gray
The main body is a neutral gray or metallic image. When the neutral gray (especially lighter neutral gray) occupies an important part of the screen, if the color cast is very obvious, the total amount of the black version of the image is increased, ie, the gray content is increased. The range of substitutions and replacements helps to ensure that there are more neutral grays in the color composition, thereby stabilizing the neutral gray balance and avoiding color casts, so full-scale blackened version curves can be used.
(2) Moderate light and dark images
This kind of image is dominated by color images, but at the same time it has both gray and dark changes. When copying, it is necessary to consider both the restoration of colors and the gray level of reproduction. Therefore, the range and substitution amount of grey components cannot be too much. Can not be too little, you can choose to adjust the black curve.
(3) Landscape, character color image
This type of manuscript has many color components, rich layers, bright colors, high saturation, and grayscale reduction. Such manuscripts are generally copied using UCR; if GCR replication is used, the replacement range and replacement amount of ash components should be reduced. In order to ensure the true reproduction of the color, a black tone curve of short tone can be generally used.
{4) Manuscripts with a neutral gray color
The variation of this manuscript level depends on the change of the neutral gray level, that is, depending on the black version, the black version can be full tone, the gray component substitution range and the substitution amount are the greatest, or the curve is close to the maximum with the custom option.
(5) Avoid overprinting
Because human vision is not as sensitive to the tone zone as it is to the dark tone zone, overprinting on the black plate is not as easy to detect as the CMY color plate. Therefore, when printing at medium and high speeds, the midtone version can be used.
(to be continued)
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