Color comes in 2 basic flavors CMYK and RGB. RGB is the native computer display space named for the 3 channels of phosphors which when excited produce color images. RGB is also known as additive color (see RGB image to the left). CMYK refers to the basic 4-color separation process commonly used for commercial printing. It is named for the four colors (cyan, magenta, yellow and black) commonly employed to print full-color images. CMYK is also categorized as subtractive color (see CMYK image below right). Other terms that have been thrown around are transmissive (because the color from you monitor is a signal source – with the signal being light) and reflective (because the image you see from a printed page is actually made up of the visible light that is reflected, i.e…not absorbed, by the inks and paper).
Additionally, art comes in 2 basic flavors, vector and raster. Raster art is the classification for photographic, continuous tone images. Vector is the term applied to images that are made of solid shapes (called fills) and solid lines (called strokes). For example, a satellite photo of your house from space is raster and a street map of your neighborhood is vector. You and I both know that digital art can contain both raster and vector elements but let’s keep things simple for a little while.
So, where do profiles (called *ICC profiles) come into play? We probably need to provide a little background here. ICC is short for International Color Consortium, a group founded in 1993 by Adobe, Agfa, Apple, Kodak, Microsoft, Silicon Graphics, Sun Microsystems, and Taligent. Sun and Microsoft have since left the group and Canon, Fujitsu, Hewlett–Packard, and Lexmark have joined. The purpose of the ICC was (and is) to develop standards for color display and reproduction across computer operating systems, hardware and software platforms.
Think of ICC’s along the lines of a child’s toy from the early 60’s (back when John Wayne road dinosaurs across the earth and we made our images by rubbing 2 sticks together over a fire made from discarded bell-bottom jeans), the printed balloon. Yes, once upon a time children would actually play with cheap blow-up balloons. The images Bugs Bunny, Sylvester, Tweety, Planet Earth and the Moon only looked right at a certain size. If you tried to blow ’em up larger the images would not stretch uniformly. They would stretch the most where the ink coverage was thinnest and usually wrinkle a bit right at the edge where the ink was heaviest. If you let the air out, the balloon would almost do the opposite. The lightly inked areas would shrink the most, the edges next to a heavily inked area would wrinkle and the inked portion with the heaviest coverage would pucker out like a bad tire ready to blow. ICC profiles are specifications for color range and appearance under certain working conditions. Or, how much air you should put in a balloon with a certain type of image on it.
ICC profiles have 2 functions, display and print production. If you would like to get a direct experience of the display function open any Photoshop file (in Photoshop, of course) and select Edit>Assign Profile. Make sure you check the Preview box and select a profile from the Profile drop-down menu. At present, the numerical values which govern color in your image are unchanged. But the appearance of the file will be adjusted to approximate how those values would image in a different profile or printed with a particular device (provided you have updated your monitor profile). However, if you convert your color file to another profile space the numerical values are changed to fit within the new space. If you are employing the latest edition of Photoshop you may not notice a visual difference when you convert to another profile. Photoshop CS5 and CS5.5 will honor the original appearance of your file by changing the color values to preserve the original appearance (intent) in a new environment. This preservation of appearance is called “color fidelity”.
In print production, ICC profiles are necessary to assist the RIP (raster image processor) in interpretation of the numerical color values especially when one device is attempting to mimic the appearance of another (for example: you are printing to a desktop device but you want to emulate the appearance of a US standard sheetfed printing press employing a coated paper).
Does employing ICC profiles give you a guaranteed result? Unfortunately, no. Even if you have profiled your monitor, keep in mind that all monitors are not created equal. Your image (especially photographic ones) may contain color ranges outside of the ability of your monitor to display (see LAB_Vs_sRGB and RGB Color Space images). Those out of range colors may affect the amount of shift you experience when you convert an image from its native color space to an output profile like U.S. Web Coated (SWOP) v2 or U.S. Sheetfed Coated v2. Consider they implied challenges when compressing a photo in Pro-Photo into a standard CMYK environment. If you compressed the same image with Relative Colorimetric intent first and Perceptual intent second, you just might get 2 very different results.
Also, consider that device profiles like U.S. Web Coated (SWOP) v2 or U.S. Sheetfed Coated v2 are approximations. A good press department and high-quality RIP can exceed expectations and a bad press department can lead to a lot of costly disappointments.