» Posted on April 3 2008 in Color-Management
One question that is bound to come up from time to time is when to use “assign profile” and when to use “convert to profile”. First off, let’s just answer this question outright - Converting is probably what you want to do… you will only use Assign Profile on an untagged image (meaning, there’s no profile embedded in the image file) and you will basically have to guess what color space the image was originally in. Typically, this will be either ProPhoto RGB, Adobe 98, sRGB or maybe even CMYK to name just a few of the more common profiles.
You use Convert To Profile when the output of your image requires a different profile than the current setting. For example; you bring your CMYK image to a photolab that prints with an RGB laser. You most likely will have to convert the profile of the image to sRGB. Another example would be if your lab was not color managed and required all images to be in sRGB, and your images were in Adobe RGB (1998). Again, you would need to convert the profile of your images from Adobe 98 to sRGB. It’s a good idea to ask your lab if they are in fact color managed. Some labs might just require you to bring in images in sRGB, while other labs will accept multiple profiles.
Now let’s look at what all this actually means. When you assign a profile to an image that already has a different profile, you are telling Photoshop to interpret the values of the colors as they would appear in the new profile, without actually changing the values. The result is ugly looking colors. An image with an embedded profile of Adobe 98, with an assigned profile of sRGB, is still basically an image with the Adobe 98 profile, but with color values interpreted for sRGB. Not good.
By converting the Adobe 98 image to sRGB, you are effectively changing the values to what they should be in sRGB. The result of this conversion is barely noticeable. Since Adobe 98 has a slightly wider gamut (range of colors) than sRGB, you should only see a shift in those colors that fall outside the sRGB gamut (most notably the greens). The out of gamut colors just get shifted to the most similar looking colors inside the sRGB gamut. Again, this slight shift in color is frequently not even noticeable.
To better understand the whole assign versus convert deal, let’s look at the following analogy. Two men go to different doctors to undergo surgery to become taller. The first man goes to a doctor who practices “assign” surgery. The second man goes to a doctor who practices “conversion” surgery. The first man’s doctor (the assign doc) says, “There, you’re now taller. Wear this big sign around your torso that says ‘I am taller’.” No real surgery was ever performed and the first man is still the same height as he was before, but now wears a sign claiming to be taller. He looks silly. His doctor basically just assigned an arbitrary height to him even though he didn’t actually operate on him. The second man, however, actually comes out of his “convert” surgery with a few extra inches in height to show for it. There actually was a surgical procedure performed and he really is taller and looks like he should look like.
In summary, you should only use Assign Profile if your image has no embedded profile, and you need to identify the profile the image was originally in. Going back to the analogy above, if the first man had gone to his doctor with the intent of finding out how tall he actually was, his doctor could have simply measured him and told him the information he was missing, namely, his correct height. It’s the same with untagged images. They just need Photoshop to find their missing profile. There’s usually no need to go through all the profiles looking for the one that looks correct. As I mentioned earlier, the missing profile is probably one of the more common ones such as ProPhoto RGB, Adobe RGB (1998) or sRGB. Those three profiles are always a good place to start.
Another common occurrence to watch out for is when your default workspace in Photoshop is sRGB, and you open an untagged Adobe 98 image (or ProPhoto RGB, Wide Gamut RGB, etc. etc.), it will most likely be assigned to the default workspace resulting in ugly looking colors. In other words, your Adobe 98 image will have the default sRGB profile assigned to it. You should then use assign profile to assign the correct profile, in this case Adobe RGB (1998). A word of warning; if you do happen to open an untagged image that’s in a different space than the default, and the image gets the default workspace assigned to it, make sure and assign the correct space first, then convert to the default workspace if necessary. Remember, convert to profile actually changes the values permanently. It should also be noted that while a profile itself might not be embedded in a file, the file is still meant to be in the original space that you used to work on it. So if you were working in Adobe 98 and somehow managed to leave out the profile in the saved image, that image should still be assigned to Adobe 98 before you convert it to a different profile if necessary.
As far as converting an image to a different profile, most of the time that will depend on your lab. As I said earlier, if your lab only accepts files saved in sRGB, then you’ll need to convert your CMYK or Adobe 98 images to sRGB.
There are two ways in which Photoshop can help out with identifying profile mismatches and/or missing profiles. The first is by setting up Color Settings under the Edit Menu. Choose a default workspace for RGB. Say, sRGB for example. Then set up your color management policies. Choosing preserve embedded profiles for RGB will leave the profile of your opened image alone. If you need to convert to the working RGB you’ll need to remember to do that later in Photoshop. Choosing convert to working RGB in the RGB drop down menu will automatically convert any opened image thats not in the default workspace to the default workspace upon pressing OK (choose this if you know you will always be working in the same workspace). By clicking all the check boxes next to Profile Mismatches and Missing Profiles, Photoshop will warn you when you open an image that doesn’t have an embedded profile, or an image with a different profile than the default workspace.
Then second way in which Photoshop can help identify the profile of your images is in the info palette. Select the palette options for the info palette, then under Status Information, select Document Profile. Now the info palette will display the profile of the opened image. If you’ve chosen Preserve Embedded Profiles under the Color Management Policies in Color Settings, this will help identify profiles that don’t match the default work space (should that be problematic for you).
© 2015 ePhotoPros.com All Rights Reserved.