CHROMiX

CMYK editing color space

In RGB it is recommended that all editing be done in an editing or working color space (sRGB, Adobe RGB) and not a device color space.

Does the same hold true in CMYK? Is there an editing or working CMYK color space?

The point of an RGB working (editing) space is that most scanner profiles are not stable environments to edit within. But your CMYK working space should be whatever your final print conditions would be. Editing CMYK in another space would give you inaccurate CMYK values and inaccurate screen previews.

That being said, editing in any CMYK space does not guarantee conformace to your final print conditions. If you create a profile with 320 TAC, then edit an image in using that profile, you can easily go over that limit and create separations that compromise quality on press. If you edit in RGB, you can twist curves as much as you want and upon conversion to the final CMYK space, your TAC will never exceed what you define in your CMYK profile. You’ll also have to remember what specifc CMYK values will equal gray on press…likely different for every press profile. In an RGB working space, gray is equal values of RGB, which will convert to ideal CMYK gray upon conversion, so its a no brainer.

A lot of graphic designers use a CMYK workflow and receive scans from a service bureau already converted to CMYK. I assumed that the images should be converted to the press profile once it is known where they are to be printed.

Yeah, this is still probably the most common scenario , and it can certainly still lead to high quality output, but there is an assumption made about the final print conditions that may or may not be accurate.

Basically you’ll want to know what’s the story behind the separations. If there’s a profile embedded, that may all you need to know and you can either honor profile and the assumed print conditions, or convert to your own press conditions (prefereably via a device link profile). If there is no profile, it’s anybody’s guess what the image looked like on their monitor.

Well yes, but if the images were separated to SWOP, and the final printing conditions are SWOP, than a conversion may not be necessary at all.

I guess my real question is this. If there are working color spaces (sRGB, Adobe RGB, …) in an RGB workflow so that images can be edited in a perceptually uniform space before they are converted to the output color space, why isn’t there working color spaces for a CMYK workflow? Is a CMYK color space perceptually uniform and therefore good to use for an editing space? If so, why not just skip converting to a working color space in an RGB workflow and convert directly to your output devices color space (RGB or CMYK) and do all your editing, color correcting there.

ps. Thanks for the responses to my earlier posts and forgive my lack of CMYK knowledge.

These are good questions. A few responses:

  1. CMYK differs from RGB in a number of key ways. It is device-specific (you can’t really create a synthetic one of any value), there are infinite black generations & hence CMYK values for each RGB color, ink limiting can limit gamut, etc.

  2. The gamut of CMYK tends to be smaller than RGB spaces in certain key areas (RGB primaries especially). So any movement to a CMYK space will limit your gamut and clip the quality of the images.

  3. CMYK spaces are probably not going to be perceptually uniform. Its just the nature of the beast. One important part is how difficult gray balance is to achieve. It tends to be arbitrary.

This all said, if you need to choose a CMYK space then it’s best to choose a space that is as similar as possible to your final printing conditions - the profiles included with recent versions of Photoshop tend to be good.

hope this helps,

regards,

Steve