Why and How to Edit Profiles, and Who Should Do It
What is it with profile editing?
Many people think of profiles as black boxes that simply convert color and if you don't like it... tough. In fact, there is a lot of information in a profile and those of you who use our ColorThink software have realized a few of the ways you can see this information.
When might I edit a profile?
Well, you might edit profiles when they either:
- Produce the wrong color when used for output - for instance, a test print appears too yellow.
- Produce the wrong color then used for simulation - for instance, if you are using a CMYK press profile to proof on screen or on another printer and the colors look wrong.
If I have these problems, does that mean I should edit the profile?
Not necessarily. When I gave a presentation at last December's GATF Color Management Conference in Phoenix I was tasked with the topic of profile editing. In fact, I spent most of my time describing the different things you can (and should) do to avoid editing profiles.
Overall, I have found that when you print well, measure well, and use good-quality equipment and software, you generally get good profiles. In most cases when we have trouble with profiles we can solve the largest issues by going back and reprinting the target (perhaps with better RIP linearization), or by remeasuring.
Profiles do not always show exactly what we want and so we are left with the option of editing.
What part of the profile can I edit?
When you edit a profile, you have the capability of editing individual tables within the profile. Each of these tables contains input curves, a look up table (LUT), and output curves. (At least printer profiles are like this, and most editing is of printer profiles.)
Why does this matter?
When proofing, how do you know whether to edit the proofing part of the press profile or the rendering part of the printer's profile, since both are in use?
Well, if you are building and testing your profiles methodically, then you should have already tested your printer profile's rendering capabilities and edited it as required. Then you know for sure it is your press profile's proofing transforms. To test a profile, print a known-good RGB image from Photoshop using the profile. If you like what you see then the issue is probably with your proofing profile.
If a profile editor allows you to move curves - for instance lightness, saturation, CMYK or whatever - then you are probably editing the input and output curves I mentioned.
If an editor allows you to do "selective color" editing, then you are probably altering the information contained in the lookup table. Selective color editing will allow you to make the reds less orange, for instance, without altering any of the other colors.
A good profile editor will allow you to select:
- which rendering direction you want to edit - output or input
- which table you want to edit for that direction - perceptual, colorimetric, etc.
- editing by curves - for color-cast removal and so forth
- editing selective colors - for those remaining color problems that may persist.
A good profile editor will also save edits along the way for further tweaking and testing.
Now, which are the best editors?
Kodak Profile Editor is one of the best - unfortunately you must purchase the full package in order to get the editor.
[Editor's note: Kodak now offers the ColorTools Colorflow Profile Editor, and this is available as a stand alone application. It is available for Mac operating systems only. Gretag and Fuji also offer profile editors. (August, 2006)]
Monaco's is also good - again not available outside their package and is only works on their profiles.
How do I know which editor is best for me?
A) For the person who wants to edit profiles but not necessarily learn new software and a new user interface, I recommend:
Kodak Custom Color ICC - this operates as a Photoshop plug-in, but the representative image file can actually be edited in any application. Most Photoshop moves can be used to alter the file - good for people really familiar with PS and not really willing to use another application. This application should not be confused with the above-mentioned Kodak software.
B) For the person who wants to edit profiles and doesn't mind a new User Interface, I recommend:
GretagMacbeth's ProfileMaker Pro Editor. A good editor all-around, with the only drawback being that you cannot save edits in as flexible a way as I would like. Like most GretagMacbeth software, it has a clean interface. One of the nicest features is the "scrubbing" or "windowshade" effect it has for viewing your changes. A slider appears over your reference image with the changes acting as an overlay that you can move on and off your image. It allows you to zoom into an area (shadow detail, for instance), make edits, and then see where they take effect.
There are several less expensive packages around but, from what I have seen, they only allow editing of the curves and, even worse, do not allow differentiating the edits between rendering intents or input/output direction.
I think their creators expect that users at that level might not understand the arcane parts of profile editing. I would counter with the argument that people at that level should not be editing profiles. They should learn more about what's involved and then use a fully capable tool. Editing profiles is something that should be undertaken with care, and the person doing the editing should have at least a basic understanding of how they work.
Also, if you are editing a profile, don't forget to test with multiple images that span the range of imagery you typically print. What may appear to be a small color shift on one print can really mess up another.