The two primary color modes in use, RGB and CMYK, each offer many “flavors.” In general, RGB color is more user-friendly and flexible. It also produces files that, at a given resolution and bit depth, are about 25 percent smaller, since it has three channels to CMYK’s four. Most stock-image distributors should only concern themselves with RGB files. Most magazine publishers have standardized on RGB as well. They have prepress staff reasonably skilled at converting RGB files to the particular variety of CMYK needed for their presses.
The most commonly used RGB profiles include:
Adobe RGB (1998) and ECI-RGB come much closer than sRGB to encompassing the color gamut of standard CMYK profiles. Those involved in high-end, fine-art inkjet printing often use ProPhoto RGB, which has an even wider gamut. But the wider gamut leaves more room for error, making it problematic for standard delivery. Note, too, that proper display of colors in Adobe RGB (1998) files requires calibrated monitors and users who preserve embedded profiles. Since you can’t yet assume either, sRGB, with its narrow gamut, remains the safe choice when you don’t know who will work with the files. Under ideal circumstances, it’s best to work with the Adobe RGB (1998) or ECI color space, but the additional color gamut can become a liability if the printer strips out or ignores the embedded profile, resulting in flat and toneless images.
For web and digital projection, sRGB is the clear choice. The web is a lowest common denominator medium, where you must assume monitors are not calibrated and web browsers are unable to read color profile tags.
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The choice of color mode blurs for graphic designers and others producing collateral materials on offset presses. The vast majority of small- to medium-size offset printers prefer receiving CMYK files, even if they often can’t specify exactly which CMYK profile they need. As result, many graphic designers use Photoshop’s Image>Mode>CMYK to convert RGB files to CMYK. By doing so, they convert to the default CMYK profile in Photoshop’s Color Settings. The initial default setting is U.S. Web Coated (SWOP) v2, or Coated FOGRA27 in Europe, even though these may not be optimal profiles. Graphic designers need to assess the choice of CMYK delivery based on the capabilities (or lack of them) of the photographer, the graphic designer and the prepress/printer to convert files.