10.31.2016

Troubleshooting Color: Source Color Space



More than once I have been asked: "OK, so the color is wrong, how do I make it right?"

Troubleshooting CMYK color can be a pain, because there are often many places the problem could be lurking, and changes made in one, may inadvertently alter the output based on info from another. So in this five part series, we will look at five important steps to troubleshooting a color managed system, or colorimetric tuning.

As you all know, a color management system is usually broken into five parts:

1. Source color space
2. Media parameter setup
3. Source color space designation
4. Output color profile
5. Output calibration set


Part 1 - Source Color Space


Color files set up to be printed always use a color space, even when the exact color space is not known by the customer. In general, the source color space is either RGB or CMYK, and composed pages are often found to contain both. For most customers, RGB is preferred, since it offers a larger color gamut, and higher saturation levels.

RGB usually comes in one of two flavors: sRBG or AdobeRGB. The key difference is in the size of the gamut, with sRGB having a smaller gamut than AdobeRGB.

Any work produced on a Windows device will usually be in sRGB by default. RGB is usually preferred since most sources (scanners and digital cameras) generate RGB, and most display screens use RGB as a native representation.

Some customers use CMYK as a source color space, with many flavors possible; SWOP, GRACol, ISO, etc., each with multiple variants. (See the Definitions page for definitions of these and other terms) The CMYK color spaces are usually characterized by the achievable gamut of a certain printing technology (ink and press type) on a certain class of media. While designing in RGB offers more possibilities, designing in CMYK often assures the final output will be within gamut.

The CMYK source space may also be used to emulate the lowest common denominator of two or more digital printers/copiers when matching output between the multiple printers/copiers. 

In any case, the source color space and variant must be known for optimum output color. 

A tag or profile is frequently embedded into the source file to identify the color space being used. The tag may be directly read in the RIP's job parameters.  Embedded profiles, if present, should ALWAYS be honored.

If the source color space is not known or discernable, experimentation must be used to find the closest match.

Other parameters specified in the Source area of the RIP job setup pertaining to color are:

  • Almost always leave at the Full Output GCR default, allowing GCR parameters in the output ICC profile to specify black channel generation. Setting this parameter to Full Source GCR5 may cause color translation problems and should be avoided.
  • Rendering Intent : Usually set to Relative Colorimetric which assures maximum colorimetric accuracy of in‐gamut colors. The default Presentation designation increases chroma of many in‐gamut colors, often rendering them inaccurate. 
  • Photographic (Perceptual) also changes many in‐gamut colors, but may be useful if the shadows tend to block‐up.

----------

Do you have a color management question, horror story or event to share?
Email me at reilley4color@gmail.com

No comments:

Post a Comment

Got a comment, or correction? Please let us know!