How to control the image quality to meet the printing requirements

Offset printing is the decomposition of continuous images into discontinuous dots. The ink is transferred through the dots of different sizes and the images are copied. In this process, the requirement for image quality is the key. The content of evaluating image quality generally includes: image reproduction, color reproduction, and sharpness processing.

The gradation reproduction of an image refers to the correspondence between changes in light and darkness in a manuscript and light and shade changes in a copy (printed matter). The gradation of the manuscript is in the range of 0-4, and it is necessary to process the tone: compression, pull The key to extending or linearly copying and gradation copying is to process the originals of various contents in order to achieve the best reproduction effect. For example, some images are dominated by tones, some are dominated by colors, and are evaluated differently when evaluated.

Color reproduction: refers to the conversion of two color gamut spaces and the corresponding relationship of color values. When we look at the original, the extension, and the scanned image of the scanner, all the optical information of the original is represented by RGB. The final printed product is expressed in four-color inks and expressed as CMYK. We evaluate the color reproduction of printed products, not to see the colors on the screen, but to see how much the color in the original is expressed by CMYK and whether these values ​​are optimal.

Emphasis on the sharpness: It is the blurring of the borderlines caused by the continuous manuscripts that make up the discontinuity of the original image. In addition, because printing materials such as four-color overprints and paper inks will lead to a reduction in the sharpness of the printed image, it is inevitable that the sharpening of the image is properly emphasized during the platemaking process. We will evaluate how sharp the image is reproduced. Whether or not the manuscript has been processed accordingly to ensure that the printed product satisfies the audience's viewing needs.