This chapter is from the book
This chapter is from the book
This chapter is from the book
The Achilles heel of CMS
The integrity of the entire color management system relies on each and every digital image file being embedded with a profile identifying the color space it occupies. Color management is communication; the profile describes the "language" the RGB triplets "speak." Without that profile, it is impossible for the user to know the specific colors the RGB triplets in the file are supposed to render; there is no accurate communication.
In verbal communication, the meaning of words is known only when the language being spoken is also known. "Pain": is it "bread" or is it "hurt"? Without knowing whether the word is in English or French, you can only guess. Likewise, without a profile, you can only guess which color an RGB triplet represents in a digital image file.
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Here is the Achilles heel: the current architecture of the CMS makes it too easy to save a file without an embedded profile. You are given the opportunity at several points along the workflow to either not embed the profile in the first place or discard it once it's been embedded. Both of these options break the chain of color management.
This is a flaw in the current set of software tools we use. The flaw is not a functional one; everything works the way it's supposed to. Rather, the flaw is in easy accessibility. There is one situation in which you want to be able to save a file with no profile embedded: when you are printing and saving a target for profiling a printer. In that case, no color management should take place; you want the printer to see the raw data in the file with no profile in the process. Every other situation requires that a profile be embedded to give the file numbers meaning. A good analogy is that when hunters store their gun, they put a trigger lock on it. This prevents tragic accidents and makes the firing of the gun a process that involves deliberately unlocking the trigger. There should be a similar lock on the "switch" in Photoshop that allows a file to be saved without a profile. There are times when you'll want to unlock that switch, but it should be a deliberate act. As the Guardians of the Color, we should always embed and never discard. Proper file saving will be addressed later in the chapter in the section "The mechanics of the CMS."
Be deliberate, be aware
To guard against being wounded in the Achilles heel, there are three simple rules to follow:
- When saving a file, always embed the profile of the color space in which that file was created (see Figure 4.11).
Figure 4.11 Be sure to check Embed Color Profile every time you save a file.
- When receiving a file, always choose to preserve its embedded profile (see Figure 4.12).
Figure 4.12 Always preserve the embedded profile; never discard.
- When moving from one known color space to another (for example, from an RGB working space to a CMYK output space), always use Convert to Profile, not Assign Profile (see Figure 4.13). I address the proper use of Assign Profile in a moment.
Figure 4.13 Convert to Profile is the proper way to convert a file and retain its color appearance.
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Occasionally you will encounter a file that is untagged, meaning that it does not have a profile embedded. Untagged files are not color managed; we don't know what "language" the RGB triplets are "speaking," making it impossible to know for sure what the RGB triplets are supposed to mean. Consider untagged files as broken and in need of repair; don't allow an untagged file to leave your hands. Each partner in the workflow must consider this to be their responsibility.
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What to do with untagged files
In our spoken language example of "pain," if we don't know the language, we can't determine the word's meaning. Faced with that situation, we'd have to make our best guess as to the meaning of the word based on context. We'd try out different languages until we found the one that made the most sense. If the person speaking the word is hungry, French is likely the language; if he's holding his head in agony, English is the best guess.
It's the same with untagged files, which are like words without meaning. We would view the untagged file using different profiles until we found the one that made the image look the best. Then we would assign that profile to the untagged file. In our "pain" example, if we determined that the word means "bread," we would assign French to that word.
To assign a profile in Photoshop, choose Edit > Assign Profile. In the Assign Profile dialog box, you can choose to view the file using Photoshop's RGB working space (as specified in Color Settings), or you can view it through any of the profiles in the pop-up menu next to the Profile radio button. To make an educated guess as to the correct profile to assign, most of the time you can narrow your choices to one of the four main RGB working space profiles that ship with Photoshop: sRGB, Adobe RGB (1998), Colormatch RGB, or ProPhoto RGB. sRGB is always a good first guess for one main reason: most point-and-shoot digital cameras capture in the sRGB color space, and most untagged RGB files come from point-and-shoot cameras. Ultimately, however, the correct choice will be determined by what looks best. Yes, this is unscientific in a workflow whose integrity relies on process control, but making an educated guess is our only option when we're repairing an untagged file (see Figure 4.14).
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Figure 4.14 When assigning a profile to an untagged image file, choose the profile from the pop-up menu that makes the image look best. For RGB files, the correct choice is most likely sRGB, but it could be anything.
Assign vs. Convert: don't confuse them
There are two commands in Photoshop that are often confused, causing the integrity of the color management chain to be compromised:
- Convert = translate: Translating from one language to another is like converting from one color space to another; both require knowing the source and the destination. The object of language translation is to retain meaning; the object of file conversion is to retain color. In the case of spoken language, "pain" in French accurately translates to "bread" in English—different words, same meaning. In the case of digital image files, R230/G190/B80 in Adobe RGB (1998) accurately converts to R242/G202/B125 in Pro38 PPSmC—different numbers, same color. When moving from one color space to another, always use Convert to Profile.
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Assign = assume/make educated guess: When a non-color-managed (untagged) file comes across your desk, you have to assume, or make an educated guess about, what "language" it is "speaking." Once you make that educated guess about what color space you determine the file belongs in, you assign that profile to the file using Edit > Assign Profile. Doing this embeds the profile into the previously untagged file. This is the proper use of the Assign Profile command; it brings the file back into the color-managed workflow. The numbers in the file have not changed; they have just been given meaning.
However, if you use Assign Profile with a properly color-managed file (i.e., one already tagged with an embedded profile), you change the meaning of the numbers. In this case, you are replacing the original profile with an incorrect one that alters the color meaning of the RGB triplets, resulting in incorrect and unpredictable color.
It would be like knowing that "pain" is in French and deciding that you want to change the language that defines that word to English. The word stays the same ("pain"), but the meaning changes from "bread" to "hurt," thoroughly ruining the accuracy of the intended meaning. It's the same word in both languages, but completely different meanings.
In our digital image workflow, if you assign a profile to a file that is already properly tagged with a profile, you are forever changing the color of the RGB triplets in the file by changing the definitions of those numbers—same numbers, different colors. Avoid this!
Here's the bottom line: use Convert to Profile when "translating" from one color space to another; it is the proper way to retain accurate color. Use Assign Profile only with untagged files, and only with the intention of getting those files back into the color-managed workflow.
It's a fragile system
In an ideal system, every step of the way is designed to advance the project and guarantee a successful outcome. However, in the color management system a successful outcome is guaranteed only if we collectively approach our work deliberately and with an awareness of the possible pitfalls.
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