Photoshop Color Management Warnings and What They Do
Now that we've discussed the inner workings of Photoshop's color management policies, it's time to proceed to the warning checkboxes underneath them. When opening files in Photoshop, you may have occasionally been confronted by puzzling warnings for a "profile mismatch." This warning and similar ones don't mean you have done something wrong. They can actually be quite helpful, and it is these three checkboxes in the Color Settings dialog that make them possible.
Basically, the three warning options give you a way to override your chosen color management policies while you work. If you uncheck them all, Photoshop will do exactly what you have told it to via your policy choices. If you like how you set things and you are certain that you always work with files that work with those settings all will be well, and your life will be simple. Congratulations, you can take this week off and not read any further.
But for most of us, turning at least some of these warning checkboxes on will provide benefit, so lets look at what each one controls.
The first of the three checkboxes is for "Profile Mismatches — Ask When Opening." With this turned on, you will be greeted by the "Embedded Profile Mismatch" dialog if you open an image with an embedded profile other than your chosen working space profile. The warning dialog lists the profile embedded in the document you are opening together with your working space profile and gives you three choices: "Use the embedded profile (instead of the working space)," "Convert document's colors to the working space" and "Discard the embedded profile (don't color manage)." If you were following along last week, you can probably guess what each option does since they correspond exactly with the three choices for RGB color management policy. In fact, the default choice in the opening Profile Mismatch dialog will be based on your policy choice. Set your RGB policy to "Preserve Embedded Profiles" and the mismatch dialog will default to "Use the embedded profile." Set it to "Convert to Working RGB" and "Convert document's colors to the working space" will be the default mismatch dialog choice. And if you weren't paying attention last week and set your RGB policy to "Off" then "Discard the embedded profile" will be pre-selected.
The advantage then of having the warning pop up is that it gives you the ability to change your mind on what you want to happen for a given image. Regrettably though, Photoshop doesn't let you wee the see the image before you have to choose. If you unsure which option you want then, you can always use the embedded profile and let Photoshop go ahead and open the image as it is so you can see it, after which you can convert to your working space using Edit >> Convert to Profile if desired.
The "Ask When Pasting" checkbox works similarly to "Ask When Opening" but tells Photoshop to ask what to do when you copy and paste (or drag and drop) between two open documents that have different profiles. Open an sRGB file and an Adobe RGB one for instance and paste something from one into the other and you will see the "Paste Profile Mismatch" dialog. As with the opening mismatch dialog, the two profiles involved will be listed at the top with section asking what you want to do underneath.
Embedded Profile Mismatch dialog
Paste Profile Mismatch dialog
Missing Profile dialog
This time though, there are only two choices: "Convert (preserve appearance)" and "Don't convert (preserve color numbers)." Discarding the source profile wouldn't make sense so long as your target document has a profile. If you have set the RGB policy to "Off" the paste mismatch dialog will not appear even if you have its checkbox turned on. This option really should be disabled if color management is off but then nothing else works right if you choose this so why should this be any different? Have I mentioned that you should not set your RGB policy to "Off?"
The third warning checkbox in the Color Settings is for "Missing Profile — Ask When Opening." This one tells Photoshop whether or not you want to see the "Missing Profile" warning dialog when you open an untagged image. Since the document you are opening doesn't have a profile, this dialog looks a bit different from the other two and lacks the list of source and target profiles at the top. It consists only of the list of options you can pick from. These include "Leave as is (don't color manage)," "Assign working RGB" (with the name of your working space profile listed after this in the option) and "Assign profile" (with a drop down list showing all compatible profiles on your system). Underneath this last option is a checkbox for "and then convert document to working RGB." Untagged images won't trigger the Missing Profile dialog if your RGB policy is "Off" even if the matching checkbox is turned on. Again, why this checkbox isn't grayed out if color management is off is beyond me.
For missing profiles, if you know the correct one you can select it in this dialog, but if you don't know, don't just guess. Your first recourse would be to ask the person who gave you the file, but they might not be as color management savvy as you are. If they don't know, choose "Leave as is" and open the document untagged. Once you have the document open, you can use Edit >> Assign Profile to assign the profile that renders the image most acceptably. Just go down the list with the Preview option in the Assign Profile window checked and pick the one that makes your image look best.
The safest approach at least to begin with is to turn on all three warning checkboxes. If you truly find that over time you take the same action each time you see the associated warning dialog you can then decide to turn one or more warnings off and let Photoshop do its thing automatically without asking.
Of course another reason you might want to turn on these warning checkboxes is just to stay informed on what Photoshop is doing with the colors in your files. Turn off the warnings, and Photoshop won't tell you when it decides to change things. For instance, set the policy to "Convert to Working RGB" and you'll never know when you open a file in another color space unless you have the Profile Mismatch warning enabled. Photoshop will simply convert everything to your working space without telling you. Even if you do want it to convert images in other color spaces, you might at least want to know when Photoshop does so.
And once Photoshop has converted profiles, there's really no going back, especially if the source space had a larger gamut than your working space does. Colors in the expanded gamut will already have been lost and can not be regained simply by converting back to the original profile.
Personally, I have the pasting warning turned off since there is little else I might want to do other than convert to the target document's profile, but I always have the other two warnings enabled. Better safe than sorry.