Color space conversion settings for prepress output images

The image file used for print output must be in CMYK color mode, not RGB mode. The process from RGB mode to CMYK mode is what we call the color separation process. Although this operation is very simple, in order to make the color separation meet the actual printing conditions, the color separation parameter setting must be done in advance. The setting of color separation parameters is essentially part of the color management process. Photoshop has integrated the settings of color separation parameters into color management after version 5.0.

Start the Photoshop software, open the Edit-> Color Settings command, and set the CMYK working space in the working space settings. You can choose the CMYK color space built in Photoshop, or you can set the user according to the actual print output conditions.

Gray space setting
It has a great influence on the value converted from color mode to gray scale mode (GrayScale). For example, for the same RGB patch R75G128B56, when Dot Gain is 20%, the value K converted to GrayScale mode is 65%; when Dot Gain is 25%, the value K converted to GrayScale mode is 60%; when Dot Gain is At 30%, the value K converted to GrayScale mode is 54%.

Setting of spot color space
It directly affects the display color of spot color images. For example, when Dot Gain is 20%, a spot color with a dot percentage of 55% is brighter. When Dot Gain is changed to 30%, the color is darker.

Color management solution
In order to manage colors more effectively through the system and applications, Photoshop can embed ICC color characteristic description files in image files. After embedding, ICC Profile can describe the correct color space for image files to ensure the consistency of colors. When other applications open the image of the embedded ICC Profile file, if the related settings are inconsistent with the embedded, it will automatically judge and decide what to do. In the previous Photoshop version, the "Profile Settings" was used to embed the ICC Profile file. Photoshop 7.0 changed this, and changed the ICC Profile to be embedded when storing the image file. If it is an RGB image, embed it according to the settings of the above RGB space. For a CMYK image, embed it according to the setting of the CMYK space.

When opening an image file in another application software, what should I do if I encounter a mismatch between the embedded ICC profile and the software settings, or if the image does not have an embedded ICC profile? This is the problem to be solved by Color Management Polices. In the Edit-> Color Settings dialog box, there are contents of color management policies. The relevant settings are shown in Figure 6, where RGB, CMYK, and Gray images can be set separately, but the basic content is the same.

Photoshop color space conversion method settings
Open the Edit-> Color Settings dialog box, select "Advanced Mode" at the top of the dialog box, and in the "Conversion Option", you can make selections about color space conversion. The choice is the color management engine (Engine) and the color conversion method (Intent) when performing color space conversion.

Basic settings of Photoshop color management
Open the Edit-> Color Settings dialog box. At the top of the dialog box there is a "Settings" drop-down menu, which mainly determines what color management settings to use. Specific settings include "color management off", "Photoshop5 default color space", "Web graphics default settings", "US pre-press default settings", "European pre-press default settings", etc., operators can choose as appropriate. If you modify these settings, it is a customized setting.

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