Adjustment of gray balance in print reproduction process

(2) Visual error
People's vision is more sensitive to M and Y color inks and more insensitive to C inks. In order to adapt to the visual effect, the C ink's on-site density value is greater than the M, Y ink, and the three-primary version of the dot area ratio, C version is greater than the M, Y version. Practice has proved that in order to get the ideal neutral gray in printing, it is necessary to change the ratio of the three primary colors of C, M, and Y inks.

In addition, the outlets are in high light (1% to 10%), bright tone (10% to 35%), medium tone (35% to 65%), dark tone (65% to 90%), and dark tone (90% to 99%). In different areas, the mechanism of color formation is different. In the highlight area, most of the visual observations are individually aligned C, M, and Y primary color dots whose reflections are R, G, B. Mix light and add color to the color combination. In the midtone region, since the dot area increases, the dots overlap each other, so the color formation is a subtractive method for the color material. Therefore, in the three areas of bright, medium and dark, the ratio of the three primary colors that form a neutral gray balance is also indifferent.

In order to obtain the neutral gray balance of the entire tone, we should adopt the gray balance curve of the scanning equipment itself, on the premise of stabilizing the company's proofing and printing suitability, and adopt the standard gray gradation rule or IT8 standard gray step and color standard scan and analysis. The experimental tests of output film, printing plate, proofing and printing are carried out. The reflectance densitometer is used to measure the density of the sample ash traps at various levels. The abscissa is used as the abscissa, and the transmission density meter is used to measure the dot area values ​​of the corresponding grading scales of the film. Using this data as the ordinate, the three-level curve of C, M, and Y will be calculated for the corresponding step density and halftone area values. Then, based on the reduction status of the gray level ruler at each level of the proof, the C curve is used as a reference, and the M and Y curves are sequentially determined. Make minor adjustments. Then the same conditions as the previous scan, film, printing, proofing, until the gray scale to obtain the tone of all levels of reduction.

3. Gray balance curve specification
Due to the different printing suitability, the percentage of grey balance tricolor dot area on the color separation sheet is also different. However, the printability of several common papers, inks, etc. can be standardized and stabilized so that the gray balance data can be fixed. E.g:

(1) According to the ISO-CD12647-2 image printing technology—the process control of screens for color separations, proofers, and printed products. Part 2: Offset 4.1.7 The percentage of grey balance area, which is commonly used internationally. Printability settings. as shown in Table 3.

(2) The gray balance curve setting of photoshop is also selected according to a certain printability conditions such as ink and paper. The ink is set to Swop (Coated). The standard includes the specified ink hue, paper whiteness, and field density. And outlets increase the value of indicators. Through experimentation, the three-primary printing dot area values ​​of the gradation scales reproduced at each step of the gray scale are shown in Table 4 and FIG. 2 .
(to be continued)