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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.

Thanks

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    You would not use the PNG format for print production.
    – Scott
    May 22, 2015 at 18:49
  • Thanks for reply! So how would I import object without background, except to draw clipping mask in Illustrator? It's easy for simple form-hard edge objects, but people (hair) in example could be almost impossible to extract in Illustrator...
    – Jazzigula
    May 22, 2015 at 19:00

2 Answers 2

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PDF Export

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.

RGB Images

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:

  • Is the conversion using the right color profile?
  • The black produced is the one you need?
  • Do the gradients look right, and have a smooth color transition?
  • Do you need "pure" colors?
  • Do you need another kind of color conversion, like perceptual or colorimetric?

Many things to consider when making a color mode conversion.

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  • Hi Rafael, Many thanks for this detailed answer, it helped me a lot, cheers
    – Jazzigula
    May 23, 2015 at 2:47
  • It should be noted that RGB files exported/saved to PDF/X format basically tells the Adobe Acrobat engine to convert your colors for you. It's not like there's a magic button that ensures the RGB data is correct. Adobe just runs an automated processes based on color settings to covert RGB data to CMYK data. It does not mean that conversion is always reliable. If you want reliable color for print production, work in CMYK, not RGB.
    – Scott
    May 23, 2015 at 5:13
  • Actually I agree that I don't rely 100% on this "blind" conversions. Normally I work for sometime in rgb, and at some point previous to the export I convert and flaten the raster images. I'll edit the post to explain a bit some aspects to consider when converting rgb to cmyk. Just a bit becouse could be out of the scope of the original question.
    – Rafael
    May 25, 2015 at 5:37
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The PNG format is for screen. It is an entirely incorrect format to use in any print production files. Not only does PNG not support CMYK, many Raster Image Processors (RIPs) do not understand the format and will choke on it.

The correct formats to use would be the native Photoshop format (.psd) or .TIFF. Both these formats support CMYK color, allow transparency, and will not choke a RIP. (You could also use .pdf or .eps but .psd and .tif are the best.)

Change the format and you won't have to worry about RGB images in your print-destined files.

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    Hi Scott, According to Rafael's answer, if I import PNG into AI document, and than save as PDF properly, it would be full CMYK at the end, which should work perfectly for print. Am I missing something? Thanks –
    – Jazzigula
    May 23, 2015 at 3:16
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    Rafael and I have different opinions. If you place a PNG in AI and then save as a PDF/X file for print, you allow Adobe to convert the PNG data to CMYK image data. I, personally, prefer to not let Adobe choose what colors work for me.
    – Scott
    May 23, 2015 at 5:11
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    Def agree on that comment "Don't let Adobe convert for you" - there can be a considerable unwelcome shift - better to control the conversion yourself. Personally I work in RGB for correction in Photoshop (more gamut) and save a version for CMYK conversion / Print (always keeping the original). Also, dont get too hung up on colour - if printing get a proof and adjust as required. If screen, it will be different ultimately on every users monitor, most people wont notice or be concerned. Its important but I wouldn't lose sleep over it.
    – Applefanboy
    Dec 23, 2016 at 10:02

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