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Managing Color in RGB-CMYK Conversions

(May 2008) posted on Fri May 02, 2008

Find out how image-file preparation and color-space conversion can affect color control in prepress and digital print production.


By Rick Mandel

Color management is all the buzz these days. After all, controlling the color on your digital printing devices is a big part of what you sell to your customers. But who exactly controls the color? Your client? The client’s files?

Client assistance is one of the most advantageous means of preparing files and maximizing the quality of digitally printed graphics. During the course of working with customers we typically explain resolution, file size, and format, though we do not address color-space conversion from RGB to CMYK and resultant color space (gamut). This conversion is among the many elements we must control, and it’s the facet of color management that I’ll discuss.

 

Conversion

Digital printing offers a less convoluted manufacturing process when compared to offset, screen, flexo, and other conventional methods. The complicated scenario with digital printing is that one file is produced and the client expects specific color reproduction without regard to the huge variety of devices that might be used to produce the print. While the devices are in the same family (i.e., wide-format solvent or flatbed UV inkjets), the deviations between them can be attributed to ink, resolution, RIP, and color-management decisions. Color management is a variable in which we can decrease the disparity between devices in the same family, especially in the conversion from RGB to CMYK.

We can construct graphics files in RGB or CMYK, so which is better? Let’s back up a bit. RGB is color in its original form. The RGB color space is an additive color model in which we add red, green, and blue light together in various ways to reproduce a broad array of colors. The choice of primary colors is related to the physiology of the human eye. I would call RGB the first generation of color. Something gets lost as we go to second generations of anything. Color is no exception. In this case, we usually lose hue and color gamut.

CMYK is the color format of printing, as digital imaging devices are ultimately CMYK printers. Yes, many devices have six and seven colors to try to increase the color gamut, but however we dress it up, CMYK does the bulk of the print lifting.


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