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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.

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By Rick Mandel

For our purposes, let’s define RGB-to-CMYK conversion as changing the color space of an image in a way that honors the original creator’s intent—within the limits of the printing process. In reality, we are converting color from its natural form (RGB) to a form for printing (CYMK). We narrow the color gamut when converting color space and leave it with no place to go.

Where and when do we convert? The answer isn’t so cut and dried, because print workflow and responsibility do play a part in the decisions. In general, RGB has a larger gamut of color than that of CMYK—that is, the ability for your eyes to see more ranges of color. The when and where of color-space conversion during the digital print workflow could boost or deflate your ability to match the client’s color expectations. Basically, the prepress workflow that results in a printed product is as follows:

1. A file is received from the client in native format (the format associated with the software that created the file, such as Adobe Illustrator) or flattened as a TIFF or a PDF. The file may be CMYK or RGB at this time.

2. The file is repurposed for your digital print process (size, reso- lution, color bars, color alterations, etc.). Some shops do con- vert to CMYK at this time within the native format. This usu- ally is an automatic conversion in the background—you may not even realize it happened.

3. The resulting file is sent to the RIP for processing into a lan- guage that the printing device understands. Conversion also may happen here.

4. Viola: printing and color.

RGB/CMYK variables exist as we analyze each step of the workflow. An ever-growing number of color-management aficionados recommend storing, manipulating, and color correcting images in the RGB color space and converting to CMYK just prior to final output (at the RIP stage). Printers who grew up in offset or screen printing are more comfortable with the CMYK color space; therefore, they tend to convert as soon as possible. Still, RGB works even for stalwart CMYK-biased prepress professionals, because image-editing tools like Adobe Photoshop allow them to accurately preview and manipulate CMYK data while working within an RGB image mode.


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