Why do printer companies not seem to care about the particular CMYK used by image?

Question

I have been trying out various different printing companies for printing out different things, many indicate that the image/pdf should be provided with an embedded CMYK profile but dont seem to care what CMYK profile is used as they say CMYK just says the level of ink to be used.

Some background:I've done some playing with RGB profiles and think I have the gist of it, that no (8bit) colour model can represent all colours and therefore different colour models can map the values in your image to slightly different colours. So for example using adobeRGB instead of sRGB allows the mapping to brighter colours, i.e 255 Red represents a more vivid red then 255 Red in sRGB but at the expense of having less values to match more muted reds, so the reds are spread more thinly. And Ive done soft proofing in Lightroom to see when images are out of gamut for a particular profile.

Then I tried softproofing to the CMYK profile my printer company uses and see if I can make adjustments in original image to remove all Out of Gamut and if I cannot without severely altering the image i would then compare relative and perpetual rendering and provided the image with the CMYK profile using the rendering method (perceptual or relative) I preferred. This way I control the rendering used, I would not have this control if I just provided the company with a sRGB profile

But other companies just say provide it as CMYK, and don't care to tell me what CMYK profile the printer uses. My original thought was if I provide it as CMYK profile 1 and they are using CMYK profile 2 then I could have a problem because they will convert it again, in which case colours would change. Or is CMYK non negotiable and I can actually experiment with any CMYK profile and use the one that does the best translation because the printer is just concerned with the final C, M, Y and Black values for each pixel ?

Answer 1

To me (US-based tech support for graphic artists), that does sounds a little odd. The number of copies and size of print says big inkjet printer to me and most of those types of printers prefer RGB input as the printer itself will convert RGB to whatever color system it uses internally (which may be more colors than just C, M, Y and K).

Technically and in a modern sense, CMYK is for printing processes that use halftone/stochastic screens and separate printing plates to reproduce color. So the paper passes through one drum and receives all of the Yellow bits of the image as a pattern of tiny dots, then Magenta, Cyan and finally the Black parts of the page (which may include text and artwork that isn't halftoned). In a strict sense, CMYK is device dependent. Different presses, inks and papers have different limits as to how much ink can be on the page and types of color that can be reproduced, so theoretically there should be a custom profile for each setup. Converting from RGB to CMYK cannot be 100% mathematically reversed, as the color gamut of CMYK is different enough that there isn't a one-to-one reverse mapping to the original data.

While modern commercial inkjet and laser printers have their own imaging engine and generally expect RGB input (even if they will be printing just CMYK), many printing presses are still often pre-computer, mechanical devices with manual control over color calibration. For this and a few other really technical reasons, color calibration is often skipped for these types of presses, as there is no fixed default setting that can be returned to each time (necessary for calibration). So operators are often accustomed to making tweaks in Photoshop and on press to adjust color.

Note -- this is speculation on my part, as I don't know the shop. It may be that the staff is simply used to working in CMYK and intends to tweak the printer settings or image as needed to get nice results (even if the printer supports RGB). If that is the case, then they wouldn't provide an ICC profile because they are used to working without one. They might just look at the profile you used to get a sense of what kind of adjustments they need to make.

If you are happy with the results you have been getting, then I wouldn't over-think the numbers too much. Follow the instructions that the staff gives you.

If you want to geek out over your images, look around for a printer that accepts RGB files and provides ICC profiles for soft-proofing. They are out there, but may be more expensive.