Technology Corner
by Julio Palleiro

The False Interpretation of the Image
Part I: Ebony, Ivory, Cyan, Magenta, and Yellow Living in Harmony

Professional retouchers and photographers are aware of the importance of Color Management. Adobe RGB, ICC profiles, and calibration devices—all of this may be cumbersome to most novices, but over the next two articles I am going to demystify some of the basics of digital color management.

This month I will break down the importance of Photoshop color management and how profiles work. For many of you this will be very rudimentary and for others very confusing. I hope that whether you are a production manager with no color management knowledge or a retoucher with vast color experience you can get something out of this article.

What are ICC profiles?

Prior to 1993-color management varied by user. The International Color Consortium (ICC), formed by industry leaders, created a universal color profile to help minimize the chaos. An ICC profile links a particular color gamut (range) to the file or device. Monitors, printers, and individual photo files can have ICC profiles. Your software, such as Photoshop, uses a Color Management Module (CMM), which interprets the profile and translates the color gamut to your computer. The CMM connects profiles to your devices through a Profile Connection Space (PCS). I only mention the CMM and PCS to paint a picture of how it works. However, there is no need to explain any more intricacies because your computer and Adobe default to a very capable PCS and CMM.

Color spaces

When working on color files you have the choice of working in RGB (Red, Green, Blue channels), CMYK (Cyan, Magenta, Yellow, Black channels) and Lab (which requires a separate article to explain). Because RGB is a much wider gamut of colors, and digital cameras capture in RGB, it is preferable to edit in RGB. When you open a file in Photoshop, by default, a dialog box asks if you want to use the embedded profile (if there is one) or convert to a different workspace. By switching workspaces you are linking a different ICC profile to that file. There are many common workspaces (or RGB profiles), but there is no need to explain each one. We at Rich Imaging, Inc use Adobe RGB (1998), which, by a large margin, is the most used RGB color space. It has been accepted and proven for the past ten years, and we have not found a reason to change it.

RGB to CMYK and Rendering Intents

Earlier I pointed out that most editing is done in RGB because RGB generally has a larger color gamut than CMYK, but as many of you may know, commercial printing is almost always in CMYK. So how do we get from RGB to CMYK? Easily - kind of.

Photoshop makes the process of converting very simple. Click on the “Convert to Profile” option and choose the profile; that’s the easy part.

CMYK profiles come in MANY sizes and shapes just like RGB and they are very specific to the printing intent. If you are printing (or proofing) in CMYK, then it may be a good idea to get a book or two on color separation. Otherwise, leave the conversion to the printing lab.

One last thing I want to mention on this topic is rendering intent. When the file is ready to be converted, you have four choices on how the CMM will deal with the excess RGB color, which are Perceptual, Saturation, Absolute Colorimetric, and Relative Colorimetric. Perceptual compresses the excess RGB color into the CMYK gamut. Saturation mimics the vividness of the out of gamut colors and is not a good method if you want an accurate representation. Absolute Colorimetric is a very good intent that matches the out of gamut colors to the exact CMYK equivalent, preserving whites and blacks. Relative Colorimetric works the same as Absolute; however, the white point may shift to preserve more out of gamut colors.

I hope I haven’t lost many of you (or bored the more advanced users). This was just a VERY basic overview into a vast topic, which I may go deeper into in later articles. And if I made any mistakes or was not clear please feel free to leave feedback below as usual.

Next month: The importance of calibration, and why images rarely look identical on two different monitors.

May 2008

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