Relationship between background removal and image tone reproduction quality
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Reasonable use of background color removal affects the tone reproduction of images. There are also differences in the coverage of the four-page dot in different periods. In the 1970s, China used a monochrome machine and a two-color machine, and the fineness of printing fine products was 320% to 340% (80% to 85% for yellow, 80% to 85% for magenta, and 85% to 95% for green). Black 70% ~ 80%); general prints are 280% ~ 320% (yellow 70% ~ 80%, magenta 70% ~ 80%, green 80% ~ 90%, black 80% ~ 90%), Germany Haier Electric The extension provides 240% (yellow 50%, magenta 50%, cyan 60%, black 80%), and the sum of the four versions of the expression is 120% difference between the longest and the shortest.
The main reason is the difference in printability. If the same printability conditions are used, printing with 240% and 360% tone, the product quality is definitely different. It is necessary to combine various conditions and produce the advantages and disadvantages. . At present, the printing press is developing at a high speed and multi-color, and the overall tone of the printing plate is developing toward a relatively short side. High-speed multi-color machine printing newspaper (newspaper) The total coverage of the network is controlled at 240%~260%. The basic color is used in the plate making, the opposite color is used less, the order is called, the network cable is relatively thick, and the background color is relatively large; Color rotary printing (offset paper or low-weight coated paper), the total dot area coverage is controlled at 260% to 280%, corresponding adjustment during plate making; multi-color sheetfed printing fine products (coated paper).
The total dot area coverage is controlled at 280% to 320%. Under normal circumstances, the plate is kept as bright or slightly emphasized as possible. The appropriate amount of compression is adjusted or maintained, the compression is dark, and the amount of background removal is relatively small. Medium to dark level. The overall tone value is longer, because the compensation of the black version has been lost; the overall tone value is shorter, and experiments have been done, such as 220% (yellow 40%, magenta 40%, cyan 50%, black 90%) ), the results overall look gray, the tone is hard, the middle tone is thin. If the coverage of the total network area is short, it will not meet the product quality requirements. Therefore, the reference to "the total coverage of four-color printing dots is better between 200% and 300%" requires research or experiment.