Color management is a very complex concept, and many staff in the prepress area still have problems setting the right options and operations in Photoshop software so that they sometimes have serious consequences in printing. This article briefly describes the classification of some issues that are often encountered in prepress businesses, with a view to providing readers with inspiration and help.
1. Overview settings and color management solutions
If an image file does not have or has an incorrect ICC profile (Profile, Profile in Photoshop 5.X, Color Profile in 6.X, Same Meaning), what should be done? In Photoshop 5. Settings can be set in the “Profile†menu in X: 1) If the image file is not embedded in the ICC profile, an assumed profile can be specified and then converted automatically; 2) If the profile of the image does not match the current color settings , you can choose "Ignore", "Conversion" and "Open the question" three options.
Whether to save the image file needs to be embedded in the ICC profile, and it is also set in this menu in Photoshop 5.X. In Pho-toshop 6.X, the option of embedding the profile will appear every time the image file is saved.
Depending on the output of the image, Photoshop 6. The "Off", "Retain embedded profile", and "Transfer" options in the X color management scheme have completely different effects. Let's talk about the places to note when setting these three options.
Options: Off
An image without an embedded profile will be processed within the currently defined working color space, and there is no assumed profile at the same time; if the profile embedded in the image does not match the current color settings, the profile of the original image will be Removed, this option is equivalent to eliminating the color management function.
Options: Keep embedded profile
This option is new to Photoshop 6.0. The processing of an image without an embedded profile is exactly the same as the option: "Off"; if the image embedded profile does not match the current color settings, the image is still displayed on the display according to the color described in the embedded profile, current Color settings have no effect on this image. (Note: This option should be used with caution because it is possible that the image is displayed very well on the monitor, but the color will eventually be greatly deviated when printed.)
Options: The profile embedded in the converted image does not match the current color settings, and the profile is converted to the current color setting. For images without embedded profile files in Photoshop 5. A hypothetical profile can be specified in X; in Photoshop 6. X has no such option.
2. Conversion of property files
You can use the Overview to Profile (Photoshop5.X) or Convert to Profile (Photoshop6.X) submenus to open the image properties file when you open the image in Photoshop. You can use this menu when you want to apply a scanned separation profile to an image or convert a CMYK image (for offset printing) to another form of CMYK image (for gravure printing).
Note: Photoshop 5. When X saves an image, the current working color space is embedded into the image as a characteristic file. Generally, only RGB, CMYK, or Lab can be selected as the target color space. If other characteristic files are selected for conversion, for example, it is different from the current working color space. , but when saving the image, Photoshop 5. X can only embed the current working color space as a profile in the image, so it is possible to embed the wrong profile! And in Photoshop 6. In X, this problem no longer exists. The converted image of the feature file is automatically saved when it is saved.
3. Color Management in Practice
There are many options for color management in Photoshop. Below, the author lists some of the situations that often occur in production and the solutions for reference.
1) RGB Scanned Images with Profiles Most mid to high-end scanner software currently used in prepress companies can customize the output profile, which lays the foundation for the user to create an ideal color management model, such as: Heidelberg The scanning software NewColor can directly define the RGB output profile in the "Profilmanager" submenu. Just set the output profile in the scanning software to be consistent with the "RGB Settings" menu in Photoshop, so that the image is similar to the screen display in NewColor in Photoshop, which is an ideal color management in production.
Note: ICC profiles on the PC must be stored in the "Windows → System → Color" folder; in the MAC machine is stored in the "System Folder → ColorSync profile" folder, so that you can set the color in different software The corresponding ICC profile is called in the drop-down menu.
2) RGB Scanned Image Files Without Profiles Many inexpensive scanners do not support scan profiles or IT8 standard manuscripts for scan correction. However, scan profiles can also be created for these scanners because the profile creation software is completely independent of the input device! By scanning a color IT8 standard document, you can also create a scanner profile. The scanners that come with these scanners usually do not support feature files. In this case, you must use the features in Photoshop.
Open the image in Photoshop, using Overview to Overview (Photoshop 5.X) or Convert to Profile (Photoshop 6.X) in the Mode menu.
Note: After the scan profile has been created, the settings in the scanner and scanning software (such as brightness, contrast, etc.) can no longer be changed, nor can the scan software's automatic function be used, as this conflicts with the profile! If you really need to change the relevant settings, you must also re-create a profile that reflects the actual condition of the scanner.
3) RGB image files with "error" profile
What should I do when I open an RGB image with a profile embedded in it and the embedded profile is not the same as the color currently set in Photoshop?
If you select “Do not convertâ€, the image data will not change, but the color of the image on the display may change significantly; if you select “Conversionâ€, the image data will change, but the color of the image display may not be too different from the previous one. . Selecting "Convert" normally has better results, so it is recommended to "Automatically convert" or "Ask at opening".
You can do it in Photoshop 6. X uses "keep the built-in profile" so that the image is still displayed according to the built-in profile, which is a convenient way for RGB images that are eventually converted to CMYK mode. Do not use this menu if the RGB image is still in RGB mode at the end.
Note: Due to the inconsistency between the image-embedded ICC profile and the settings in Photoshop, the feature file mismatch dialog box appears when the image is opened in Photoshop. Normally, the conversion is selected.
4) RGB image file without a profile
If an RGB image file is not embedded in the property file, under normal circumstances, you can select a feature file most frequently used by the operator in the "From" drop-down menu in the open file prompt box, and select the corresponding in the "To" menu. CMYK or RGB mode.
5) CMYK scan data with profile
If you get a batch of scanned images while the scanner operator tells you the color separation settings for the scan, or provide you with the appropriate ICC profile, you can do this in CMYK Settings or CMYK Work Color Space. Make settings.
Note: In the CMYK setup menu, you can select or set the profile that matches the scanner. This will give you a better screen display.
From this point, we can also extend it slightly. We can sweep the image into RGB mode when the scanner scans. With the help of the ICC profile, we can use the same separation on each computer, whether it is a PC or a MAC. Setting, because sometimes image correction with RGB images has advantages over CMYK, such as using all filters. The RGB image is converted into a CMYK image before the final output; the same unfamiliar RGB image can be separated using a common separation property file. Many are avoided due to the uncertainty created by using the Photoshop "Color Settings" menu!
6) CMYK scan image without profile
If you get CMYK scanned images without a profile, no matter how good the quality of these images, you have to continue processing in Photoshop, which is a common situation in prepress companies, because these images are already in CMYK mode, You can try to use the cancel color management feature, that is, select "do not embed profile" in Photoshop 5.X, and this option is stored in Photoshop6.X.
The purpose of this setting is to protect the image colors. If you do not cancel the color management function in Photoshop and select the wrong Phot-oshop feature file will lead to wrong color conversion!
7) CMYK image with "error" profile
In principle, as with the aforementioned RGB image, “Conversion†is usually selected, and the color loss caused by the conversion between CMYK and CMYK is not as severe as the conversion from RGB to RGB.
One thing to note here is that the different profiles of CMYK images (including grayscale images) determine the number of different blackplates. For example, when the grayscale image is converted to a CMYK image, different separation methods (characteristic files) are used. Produce a different number of black editions; for example, if a CMYK image uses a GCR color separation method with a higher number of black editions, if the color is not directly matched when a mismatch occurs, all of this information will be lost! It is best to choose "Ask when opening" for the above mentioned situation. This allows you to see what kind of profile the CMYK image embeds when you open the image. You can also select "Do not convert" to open the image to see if the image meets the output requirements and correct it manually if possible.
There is a new feature in Photoshop 6.X, “Preserve embedded profile.†If you select an image that does not match the open profile, the display will be displayed according to the image's original embedded profile, such as with a profile suitable for gravure printing. The image previews the actual effect of gravure printing on the display; images with a file suitable for newsprint print characteristics preview the actual effect of newsprint printing on the display.
8) CMYK image files without a profile
For a CMYK image without a property file, you can specify a hypothetical property file. For image files that were saved long ago (such as Photoshop 4.0 does not support property files), you must specify a hypothetical property file before converting.
4. Summary
Using the color management options in Photoshop makes it easy to achieve the following main goals:
Improve the quality of the image;
The displays in a working group are definitely inconsistent. Using RGB profiles allows the images to be nearly identical on different monitors!
In a working group, the same CMYK image is certainly not displayed on different displays. This is due to the device-independent ICC profile.