Detailed Prepress Operation - Separation Work Paper 2 (I)

Second, color separation manuscript color separation operation

The color original color cast is caused by the poor balance of the three primary colors of the photosensitive material, the unbalanced gamma ratio, the color temperature error of the photo exposure light source, and the improper photographing processing, as shown in Fig. 6.4 and Fig. 6.5, thereby causing the image to be partially or partially biased. color.

The color correction of color-originating manuscripts is difficult to perform with only the color correction function in the electronic color separation machine. The functions of white balance, white/black calibration, CAST, gray balance curve adjustment, gradation correction, background color removal, background color gain and restriction need to be comprehensively applied to realize color correction of color-originated originals.

1. Correction of high-profile color-shifted originals

A typical high-resolution color-shifted manuscript is shown in Figure 6.6. That is, the measured R, G, and B spectral densities are C87%, Y83%, and M98% in the image white field. That is, there is no M between C and Y. Get the ideal gray balance. There are two ways to solve this color cast, as shown in Figure 6.7. The first is to use the MAN/AN mode to adjust the C and Y values ​​to set C96%, Y98%, and M98% when setting the white field. That is, move the color separation curve of C, M, and Y respectively. Second, after setting the white field calibration, use the CAST function to adjust the relationship between C, Y, and M according to the degree of color shift and the purpose of replication. Color balance.

2. Mid-tone color correction manuscript correction

The midtone color cast refers to the condition that the R, G, B spectroscopic density of the neutral gray density portion or the halftone dot of C, M, Y is unbalanced, or the "need to add a little red" or "yellow" appears when the skin color is reproduced and reproduced. Too much "state. As shown in Figure 6.8, C48%, M70%, and Y54%.

The method of midtone correction is: (1) Use CAST function to take any one of Y, M and C as the standard and adjust the other two colors to balance value, as shown in Figure 6.9, when the value of C is 48% When, Y, M adjusted to an equilibrium value of 59%. (2) When correcting, first use the gradation correction to determine the tone pattern, then use the cAST function to adjust the three-color curve shape, and finally use the color correction function to calibrate the color, as shown in Figure 6.10. (3) Correct the middle tonal offset with white/black calibration. The midtone shift color is mostly caused by the inaccurate color temperature of the shooting light source, and often occurs simultaneously with the high-profile color shift or the dark tone shift color shift. Therefore, the correction function should be comprehensively applied and cooperate with each other.

(to be continued)