In the field of books, periodicals and packaging printing, color printing has become the mainstream of printing, and the quality of printed matter is also increasing. However, due to the influence of subjective and objective factors, not many of them have reached the quality level, and they still cannot be compared with foreign high-quality products. We know that the quality of color prints is restricted by many factors in the copying process, such as the gradation level of the color original image, the dot expansion value, and the color balance. Among them, the quality of the pre-press image production directly determines the color print Although the quality can be partially corrected in plate-making and printing, it is basically impossible to print quality products. Therefore, when creating images before printing, if you find that the quality of the original is not enough, you should try to correct it. Below, a brief introduction to some processing techniques and methods. (1) Original density The difference between the maximum and minimum density in the original (that is, the contrast), the maximum density value that can be achieved in ordinary prints today is 1.8, the image of the printing paper can be up to 1.7, and the black ink density of the trimmed original is 1.8. In general, all the density of the original can only be reproduced in the range of 0 to 1.8 on white paper. Therefore, for the original, there is a density range suitable for plate-making printing. When the density range of the original is too large, the sensitivity of the scanner and the electrical extension unit to the part that exceeds the density range decreases, so the level of the color separation plate is relatively flat. According to practice, the manuscript is 0.3 to 2.1, which is the most suitable when the contrast is 1.8. The density difference of color negative manuscripts should be controlled within 2.4; if the original contrast is less than 2.5, reasonable compression will be achieved when copying, and the effect will be ideal. Poor. (2) Color cast of original Generally divided into overall color cast, low-key cast color, high-key cast color and high-low cast color (ie cross color cast). Therefore, when correcting, it is necessary to look at the overall consideration. If you cannot see a color cast, immediately process a color, otherwise it will cause other color casts. (3) Original level There are three main indicators to measure the quality of replicas: layer, color and clarity, and layer is the most important. The level of the normal manuscript should have the characteristics of no bright or dark picture, high, medium and low key, many levels of density change and rich tone.
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