Color Figure Information

Here is some special information on color figures originally provided by Carolyn Chmiel of the University of Chicago Press Production Office and updated by me. For the latest information, please check your journal's web site.
 

RGB vs. CMYK

Most computer-generated figure files are created using the RGB (red, green, blue) color model, but CMYK (cyan, magenta, yellow, black) is used for commercial printing on paper. Each of four printing plates is inked with one of the four process colors, and the ink is transferred to paper in layers. Most color laser printers work the same way.

The RGB color model is used for devices such as computer monitors that create color with light. The available RGB color gamut is much larger than the gamut for CMYK; in other words, there are colors that look fine on an RGB monitor but cannot be printed. The major culprits are brighter colors like deep green, blue-violet, and orange-pink. Color figures prepared as RGB encapsulated PostScript (EPS) files can be converted to CMYK, but because the available color spectrum is much diminished, it is very difficult, and sometimes impossible, to match the colors between the two formats. Once a channeled CMYK EPS file is created, it can be used to create the four printing plates needed to reproduce an image.

Hard copies produced from RGB files by some desktop color printers can still contain colors outside of the range of the CMYK palette. Desktop printers that use dyes or wax transfers can create colors not able to be duplicated by the CMYK color gamut.

RGB files are fine in the on-line journals. However, even then the color files are device dependent and may not appear on the reader's printer or monitor exactly as they do on the author's monitor. Authors should still pay attention to how the figures will look when printed in black and white. Such printed figures should indicate to readers the nature of the information shown by the color figure, even if the information itself requres viewing the color figure. In other words, a grey smudge in the printed version is of no value and should be avoided.