Color management is a very complicated concept. Many workers in the prepress field still have problems in setting options and operations correctly in Photoshop software, which sometimes causes serious consequences in printing. This article gives a brief description of some of the problems often encountered in prepress enterprises, in order to inspire and help readers.
1. Profile setting and color management plan
What should I do if the image file does not have an embedded ICC feature file (profile, Photoshop 5.X is called profile, 6.X is called a color profile, the same meaning)? The settings can be set in the "Profile Settings" menu in Photoshop 5.X: 1) If the image file does not embed an ICC characteristic file, you can specify an assumed characteristic file and then automatically convert it; 2) If the characteristic file of the image and the current color If the settings do not match, you can choose three options: "Ignore", "Convert", and "Ask when open". Whether to save the image file needs to embed the ICC property file. It is also set in this menu in Photoshop 5.X; and in Photoshop 6 In .X, the option of whether to embed the characteristic file will appear every time the image file is saved.
According to the different purposes of image output, Photoshop6. The "Off", "Keep embedded profiles", and "Conversion" options in the X color management scheme will have completely different effects. Let's talk about the points to note when setting these three options.
Options: Off
Images without embedded profile will be processed within the currently defined working color space, and there will be no assumed profile; if the profile embedded in the image is inconsistent with the current color settings, the profile of the original image will be Deleted, this option is equivalent to canceling the color management function.
Option: Keep embedded profile
This option is a new feature in Photoshop 6.0. The processing of the image without embedded profile is exactly the same as the option: "Off"; if the embedded profile of the image is inconsistent with the current color setting, the image is still displayed on the monitor according to the color described in the embedded profile The color setting has no effect on this image. (Note: This option should be chosen carefully, because the image may be displayed very well on the monitor, but the color will be greatly deviated during the final printing.)
Option: Conversion
If the characteristic file embedded in the image is inconsistent with the current color setting, the characteristic file is converted to the current color setting. For photos without embedded feature files in Photoshop5. X can specify a hypothetical property file; and in Photoshop6. X no longer has this option.
2. Conversion of characteristic files
Generally, when you open an image in Photoshop, you can use the "Profile to Profile" (Photoshop 5.X) or "Convert to Configuration File" (Photoshop 6.X) submenu to convert the image characteristic file. This menu can be used when you want to apply a scanned color separation profile to an image or convert a CMYK image (for offset printing) to another form of CMYK image (for gravure printing).
Note: Photoshop5. When X saves an image, the current working color space is used as a characteristic file to embed the image. Generally, RGB, CMYK or Lab can only be selected as the target color space. If other characteristic files are selected for conversion, such as: different from the current working color space , But when saving the image, Photoshop5. X can only embed the current working color space as a characteristic file in the image, so the wrong characteristic file may be embedded! And in Photoshop6. This problem no longer exists in X, and the image converted after the feature file is automatically saved when the feature file is saved. [next]
3. Color management in practice
There are many options for color management in Photoshop. Below I list some situations and solutions that often occur in production for reference.
1) RGB scanned image with characteristic file
Most of the high-end scanner software currently used in pre-press enterprises can customize output characteristic files, which lays the foundation for users to create an ideal color management mode. For example: Heidelberg scanning software NewColor can be directly in the "Profilmanager" sub The RGB output characteristic file is defined in the menu. As long as the output characteristic file in the scanning software is set to be consistent with the "RGB Settings" menu in Photoshop, so that the image in Photoshop is approximately the same as the screen display in NewColor, this is the most ideal color management in production.
Note: ICC characteristic files must be stored in the "Windows → System → Color" folder on the PC; in the "System folder → ColorSync description file" folder on the MAC, so that the color settings in different software Call the corresponding ICC characteristic file from the drop-down menu.
2) RGB scanned image files without feature files
Many low-cost scanners do not support scanning characteristic files, nor do they provide IT8 standard manuscripts for scanning correction. But it is also possible to make scan profiles for these scanners, because the profile creation software is completely independent of the input device! Scanning the color IT8 standard manuscript can also create the scanner's characteristic file. The scanning software that comes with these scanners usually does not support feature files. In this case, you must use the functions in Photoshop.
Open the image in Photoshop and use "Profile to Profile" (Photoshop 5.X) or "Convert to Configuration File" (Photoshop 6.X) in the "Mode" menu (Figure 2).
Note: After the scan profile file is created, you cannot change the settings of the scanner and the scan software (such as brightness, contrast, etc.), nor can you use the automatic functions of the scan software, because this conflicts with the profile file! If you really need to change the relevant settings, you must also re-create the characteristic file that reflects the actual condition of the scanner.
3) RGB image files with "error" feature files
When opening an RGB image embedded with a characteristic file, and the embedded characteristic file is not the same as the color currently set in Photoshop, what should I do?
If you select "no conversion", the image data remains unchanged, but the color of the image on the display may change significantly; if you select "convert", the image data changes, but the color of the image display may not be much different from the previous . Under normal circumstances, select "convert" will have better results, so it is recommended to "automatic conversion" or "ask when open."
You can do it in Photoshop6. X uses the "preserve the built-in overview", so that this image is still displayed according to the built-in feature file, which is a convenient way for those RGB images that will eventually be converted to CMYK mode. If the RGB image is still in RGB mode, do not use this menu.
Note: Due to the inconsistency of the ICC characteristic file embedded in the image and the settings in Photoshop, the characteristic file mismatch dialog box will appear when the image is opened in Photoshop. Normally, choose to convert.
4) RGB image files without characteristic files
If an RGB image file is not embedded in a characteristic file, under normal circumstances, you can select a characteristic file most commonly used by the operator in the "From" drop-down menu in the prompt box of the open file, and select the corresponding one in the "To" menu. CMYK or RGB mode.
5) CMYK scan data with characteristic files
If you get a batch of scanned images, and the operator of the scanner tells you the color separation settings during scanning, or provides you with the corresponding ICC characteristic file, you can select the "CMYK settings" or "CMYK working color space" Make settings.
Note: In the CMYK setting menu, you can select or set the characteristic file consistent with the scanner, so that you can get a better screen display.
From this point, it can be extended slightly. We can scan the image into RGB mode when the scanner scans. With the help of the ICC characteristic file, we can use the same color separation on each computer, whether it is a PC or a MAC. Settings, because sometimes using RGB images for image correction has advantages over CMYK, such as using all filters. RGB images are converted into CMYK images before final output; the same unfamiliar RGB images can be separated using commonly used color separation characteristic files. Many uncertainties due to the use of the Photoshop "Color Settings" menu are avoided! [next]
6) CMYK scanned image without characteristic file
If you get a CMYK scanned image without a feature file, no matter how good the quality of these images is, continue to process them in Photoshop. This is a situation that often occurs in pre-press enterprises because these images are already in CMYK mode. You can try to cancel the color management function, that is, select "do not embed profile" in Photoshop 5.X, and Photoshop 6.X has this option during storage.
The purpose of this setting is to protect the color of the image. If you do not cancel the color management function in Photoshop and select the wrong Phot-oshop feature file, it will cause the wrong color conversion!
7) CMYK image with "error" characteristic file
In principle, it is also the same as the RGB image mentioned above. Usually, "conversion" is selected. The color loss caused by the conversion from CMYK to CMYK is not as serious as the conversion from RGB to RGB.
One thing to note here is that the characteristic files of different CMYK images (including grayscale images) determine the number of different black plates, for example: when grayscale images are converted into CMYK images, different color separation methods (characteristic files) are used Different numbers of black plates are produced; for another example, a CMYK image uses the GCR color separation method with a higher number of black plates. If the color is mismatched, the conversion is directly selected, and all this information will be lost! It is best to select "Ask when opening" for the above mentioned situation. In this way, when opening the image, you can see what characteristic file is embedded in the CMYK image. You can also choose "no conversion" to open the image to see if the image can meet the output needs, and if possible, correct it manually.
In Photoshop 6.X, there is a new function "Keep embedding overview". If you select this image to open the characteristic file that does not match, the display will be displayed according to the original characteristic file embedded in the image, such as: The image previews the actual effect of gravure printing on the display; the image with the characteristic file suitable for newsprint printing previews the actual effect of newsprint printing on the display.
8) CMYK image file without characteristic file
For CMYK images without a characteristic file, you can specify a hypothetical characteristic file. For image files saved a long time ago (such as Photoshop 4.0 does not support characteristic files), you must specify a hypothetical characteristic file, and then convert it.
4. Summary
Using the color management options in Photoshop can easily achieve the following main objectives:
· Improve image quality;
· The display of the monitors in a working group is definitely inconsistent. Using RGB characteristic files can make the images on different monitors reach the near possible consistency!
· The same CMYK image displayed on different monitors in a working group is definitely inconsistent, and these problems can also be solved with the help of ICC characteristic files that are not related to the device!
· The image can be exchanged between PC and Mac under the premise of minimum color loss;
· An image can be converted by different ICC characteristic files, so that the same image can be applied to different output processes;
· You can use a cheaper printer as a digital proofing device. Although there are different RIP solutions for color management, but the prices are relatively expensive, using some color management functions in Photoshop and other software can use low-cost inkjet printing to obtain proofs that can preview the final printed matter. The expensive color management workflow must be said to be a serious challenge!
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