If you’re a photographer looking to order press-printed products (eg business cards, photo books, calendars, etc) you might find it confusing that some labs ask for CMYK files, and some ask for RGB* files. Why?
*This refers to the colour mode, not to specific colour spaces such as sRGB or Adobe RGB.
They might ask for RGB because …
- they know some of their clients (eg Photoshop Elements users) simply don’t have capacity to convert to CMYK.
- they know they can do a better job of conversion to CMYK than some of their clients can; and they know it’s a hassle to explain CMYK to clients who don’t understand it.
- even though they’re printing with ink, they might be printing with more than just cyan, magenta, yellow and blank ink. Some printers have more than one shade of cyan, etc. Photoshop, even in the hands of the most skilled user, cannot convert to those more-than-four-colour profiles. It can only be done by the printer’s own software, and is best done from RGB files.
- they might have multiple presses, all running different profiles. They can’t know, at the time you’re submitting your job, which press it will be running on, so they can’t possibly expect you to convert to the correct profile. So they do it at the point of printing.
They might ask for CMYK because …
- they don’t want the hassle of having to go back-and-forward with their clients to discuss out-of-gamut colours. In this regard, it’s better to let the client do the conversion, so they can see if colours die, and can take steps to lessen that problem at its source.
All of this assumes that they are competent
Truth is, they might not have a damn clue. Make sure you read as many reviews as you can before choosing a printer for your press products. Make sure people are saying that they produce good work. The fact is, no matter what kind of files they ask for, you’re taking a massive leap of faith about their colour-management. Some labs just have NFIWTF they're doing.
- If they ask for RGB files, cross your fingers and hope it’s because they have very accurate CMYK profiles that they convert to.
- If they ask for CMYK files, make sure you ask all the right questions about the conversion.
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