The quality of color printing is constrained by many factors, among which the quality of color manuscripts, such as image tone and color balance, directly determines the quality of printed products. Therefore, when prepress production, if it is found that the quality of the original is not good, it should be resolved as soon as possible. The following is a brief introduction to the prepress processing techniques and methods for some non-normal manuscripts.

Printing requirements for manuscripts

1. Original density range

Color printing usually divides the original density range into 4 segments, namely bright highlights, midtones, dark notes, and extremely high light areas below the density of high spots, and the difference between the maximum density and the minimum density is called the density contrast. In general, the maximum density value of offset printing products is 1.8. That is, all density conversions of the original document can only be reproduced in a range of 0 to 1.8 in domestic paper. In addition, the original input device has a limited density range. The contrast of the manuscript is too large, and the sensitivity of the scanner and the electric extension to the out-of-range density response is reduced, resulting in loss of the image hierarchy. Therefore, for a manuscript used for printing, there should be a density range suitable for platemaking, that is, a contrast. Practice has shown that the density of reflected originals should be 0.3-2.1 with a contrast of 1.8; the original contrast of color negatives is best within 2.4. If the original contrast is less than 2.5, a reasonable compression is performed when copying, the effect is also ideal; if the original contrast is greater than 2.5, even if the copy compression is performed, the level will be lost too much, and the effect is not good.

2. Original color cast

The original color cast is generally divided into overall color cast, dark pitch color cast, bright tune cast color and cross cast color (dark tune, bright tune cast color different). Therefore, it is necessary to consider comprehensively when coloring, and you cannot correct one spot with a color cast so as not to cause other color casts.

3. Original level

The main indicators of manuscript quality are level, color, and sharpness, and the most important is the level. Normal manuscripts should have features such as the picture is not bright, not dark, high, medium, dark tone, rich tone and other features.

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