Explore: The Necessity of Pre-printing

In the field of books and packaging and printing, color printing has become the mainstream of printing, and the quality of printed matter is also increasing. However, due to subjective and objective factors, there are not many fine-quality products that can still be compared with foreign high-quality products. We know that the quality of color prints is affected by many factors in the process of copying, such as the tone levels of color original images, dot gain values, and color balance, and the color quality of the prepress images is directly determined. The quality, although it can be partially corrected in the process of plate-making, but to print a fine is basically powerless. Therefore, when making images before printing, if you find that the quality of the original is insufficient, you should try to correct it. Below, we briefly introduce some processing techniques and methods.

One. Requirements for manuscripts

(1) Original density

The difference between the maximum and minimum density in the original (ie, the contrast), the maximum print density that can be achieved in today's print is 1.8, the print image can be up to 1.7, and the black ink density of the original is 1.8. In general, all the density of the original document can only be reproduced in a range of 0 to 1.8 on white paper. Therefore, for the original document, there is a range of density suitable for printing. When the density range of the original document is too large, the sensitivity of the scanner and the extension unit to the out of density range decreases, so the color separation layer is flat. According to practice, the manuscript is 0.3 to 2.1, which is the most suitable when the contrast is 1.8. Color negative original density difference is controlled within 2.4; if the original contrast is less than 2.5, a reasonable compression effect when copying, the effect is also ideal, if the original contrast is greater than 2.5, even if the copy compression time, it will make too much level loss, the effect Not good.

(2) The color cast of the original

Generally divided into the overall color cast, low-key color cast, high-profile color cast and high and low tone each biased different colors (that is, cross-color cast). Therefore, to take a holistic view when correcting, you can't see a color cast and immediately process a color, otherwise it will cause other color casts.

(3) Original Level

To measure the quality of copies, there are mainly three indicators: level, color, and sharpness, and the most important is the level. The level of normal manuscripts should be characterized by the fact that the picture is not bright and dark, high, medium, and low-key, there are many density variations, and the tone is rich.

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