Color Printing Press Screen Soft Proofing Quality and Key Technologies (3)

Set up appropriate color management processes and mapping methods

The color management process is used to implement and control the color space conversion of various colors. For the color newspaper professional production line, the most economical and rational color management process based on screen soft proofing should be the use of color management functions built into prepress software such as Photoshop and CorelDRAW.

Such as Photoshop's built-in color management process, which "view → proof color" to start a soft proofing effect, "view → proofing settings" is used to select the simulation object and intent. It uses the RGB -> Lab -> CMYK -> Lab -> RGB (for RGB color) or CMYK -> Lab -> RGB (for CMYK color) flows shown in FIG. 2 to complete the screen simulation of the output of RGB files and CMYK files. Its characteristic is that the RGB color space must be converted to the color space CMYK color space to be “constrained”, and then converted to the RGB color space again to display the “constrained” color and image effects, thereby providing the screen display with the printing effect for editing.

In CorelDRAW, it can directly provide a screen-based soft proof color management control process marked with a red line. It first converts the Lab color value to the CMYK printing color space, and then converts it to the corrected screen and the RGB color space represented by the Profile and displays it to form a simulation effect.

Another important issue is the choice of mapping methods. The mapping method is mainly to solve the two core issues of color space compression and white point transfer. In the case of white point control, Relative, Satation, and Perceptual can be used to convert the white point of the source color space to the white point of the target color space, while Absolute is It is a white point that mimics the source color space in the target color space. For screen soft proofing, if it is a screen emulation of the RGB file's color report effect, the white point of the RGB color space needs to be converted into the white point of the CMYK color space by using the Relative, Sataration, and Perceptual methods so as to be on the screen. See the effects of different paper whiteness. If it is a CMYK file, Absolute mode is needed to “pass” the white point of the CMYK color space onto the screen to form the background color emulation effect of newsprint.

Use standard prepress methods and performance standards

After the soft proofing process has been established using the above method, both the pre-screening and pre-press processing of color and image effects should be WYSIWYG. The small print gamut that is unique to newsprint (reflected as lower saturation and brightness) and the more varied paper whiteness (color shift) can be reflected on the screen, and the effect of adjustment is not necessary. Worry about not printing. In terms of quality requirements, following the industry standards for color newspapers, there are the following requirements:

(1) Ink requirements: full and moderate, pure hue, no color cast.

(2) The image quality requirements: clear, moderate contrast; the image is not false, good resolution, can restore the natural tone.

To achieve these requirements can be summarized into the following standardized processes:

(1) Black and white fields and contrast processing: It mainly controls the overall tonal range and image range, and implements the control of “separation of layers and moderate contrast”. The treatment method is to use Level tool and black and white field pipettes.

(2) Treatment of color shift and saturation: The control of "full and moderate, pure hue, no color cast" is implemented. The processing method is as follows:

1 Use a pipette tool to neutralise the color cast. The color shift can be determined from the neutral gray region of the image, and the dropper is used to target the region as neutralization of the gray level, that is, the neutral gray region of the color shift is set with a neutral value.

2 Use the Hue/Saturation tool for vivid color control.

(3) Sharpening: Implementing the control that "the image is good and the resolution is good". The quality of newspapers' artwork submissions varies greatly, especially in terms of clarity and resolution. The processing method is to use the SUM sharpening tool.

Source: Printing Technology - Publishing Commercial Printing