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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 '15 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 '15 at 19:00
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I'm starting backwards on this answer. From the final question.

Exporting to pdf

When you export a pdf format for print, you should use a specific subformat for example the X family X-1a.

This format excude unnesesary features and process the file so it only have the data you need for print. This are old formats but work well. This dosen't alow transparencies and convert all color mode to cmyk by default.

Grayscale 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 becouse I want to control the flatening of transparency and overprint myself, but they do their job. (See aditional foot note on the bottom)

This process also any rgb external an linked file when you compile a pdf. So if you had an external rgb file will be inside the pdf in CMYK aswell.

If you need spot colors however you need to be careful about RGB files, becouse as you don't want to convert the spot colors to CMYK, the RGB files won't be processed either.

Rgb files

When you import a bitmap file (import, not link it) The image is now part of the document. The original file format is "lost". It is not important anymore. So it dosen't matter if you had a bmp, jpg, png, flat psd or whatever. Just be careful about the resolution.

On old versions of ilustrator any RGB file was converted when imported into the main color mode configured when creating the Ilustrator file. CMYK in this case.

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 controled pdf file. Sometimes is better to have an original RGB file.


One final note. You can always open a pdf again in ilustrator and see what is inside, how the raster images were processed etc. If I have any doubt I just open my exported file and poke inside.


Aditional note:

There are some aspects that need to be considered when doing this RGB->CMYK conversions, and you need to be sure your export handle this the way you need it to be. 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? etc.

There are a lot of things to consider when making a color mode conversion.

  • Hi Rafael, Many thanks for this detailed answer, it helped me a lot, cheers – Jazzigula May 23 '15 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 '15 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 '15 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.

  • 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 '15 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 '15 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 '16 at 10:02

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