So I have Illustrator document in CMYK mode intended for print. I need to import PNG image (because I need to place object extracted from the background). And here I step on the unknown area because I actually don't know will Illustrator automatically convert PNG image colors (which is RGB only format) to CMYK.
In Illustrator's Color settings, working CMYK profile is set to "U.S. Web Coated (SWOP) v2". In Color Management policies my settings are: -RGB: Preserve Embedded Profiles -CMYK: Preserve Numbers (Ignore Linked profiles)
When saving new Illustrator document, Embed ICC profiles is checked. When send to print, I export PDF with "High Quality Print" settings which, as far as I know, is set to embed color profiles.
Because I usually have no direct connection to the printer, my ultimate goal is to find and use default workflow, which will work in most situations. I spent numerous hours exploring colors topic, but still I am not so sure about each specific situation.
When exporting to PDF for printing, use a specific subformat, such as PDF/X-1a.
This format has minimal features to process the file, keeping only information needed for printing. This format doesn't permit transparencies and converts all color modes to CMYK by default.
Greyscale images will be converted using the K channel and spot colors, Duotone and RGB colors will be converted to CMYK. I don't rely 100% on this automatic conversion because I want to control the flattening of transparency and overprint myself, but they do their job.
This process also reads any externally linked RGB file when you compile a PDF, converting it to CMYK.
Spot colors, need special care to prevent converting spot colors to CMYK. RGB files won't be processed either.
When you import a bitmap file (import, not link it), the image becomes part of the document. The original file format is not retained. It doesn't matter whether the file was BMP, JPEG, PNG, flat PSD, or whatever. Be careful about the resolution.
Old versions of Adobe Illustrator would convert any RGB file the main color mode configured when creating the Illustrator file upon import (such as CMYK).
I am not sure about the new versions. But it is not a problem to have an RGB file inside if your output is a controlled PDF file. Sometimes is better to have an original RGB file.
You can always open a PDF file in Adobe Illustrator to see what is inside, how the raster images were processed, and other information about the PDF file.
Some aspects must be considered when converting RGB to CMYK. You need to be sure your export handles this the way you need it. Considerations:
Many things to consider when making a color mode conversion.