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RGB to CMYK conversion

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    • October 11, 2017 at 7:26 am #98781
      Jova 313
      Member

      I’ve read and assumed that the automatic conversion when making a pdf (with profile sheetcmyk) would give the same result as converting in photoshop before making a PDF. But i’ve tested this and i noticed that there is a difference (better result) when i convert the colors in photoshop using ‘edit > convert to profile’. Using ‘image > mode > RGB’ gives the same result as the automatic conversion from InDesign to PDF.

      Working CMYK profile is Coated FOGRA39 (same one is used with convert to profile and as output for PDF).

      Any thoughts why there is a difference?

    • October 11, 2017 at 7:51 am #98782
      David Blatner
      Keymaster

      As long as the placed image has an embedded RGB color profile, and you are outputting to the proper CMYK profile, then the results should be identical.

      I believe the only possible differences could be the rendering intent (which you can control in Photoshop, but few people do), and the fact that the export to PDF is also converting the image to JPEG. Have you tried exporting to PDF with Zip compression instead? (zip is lossless)

    • October 12, 2017 at 1:40 am #98825
      Jova 313
      Member

      I’ve done some more research and tests and found that:

      1) In general, the best way to convert from RGB to CMYK is with relative colorimetric intent and with Black Point Compensation on. (Please correct me if i’m wrong)

      2) The difference i had seemed to appear because ‘Black Point Compensation’ was not turned on by default when using ‘convert to profile’. It is on by default, in my general color settings, so also when using image>mode>CMYK.

      When i did used Black Point Compensation (as you should), there were no differences in the final PDF made with my PDF preset (does the conversion to cmyk when making a PDF).

    • October 12, 2017 at 12:23 pm #98838
      David Blatner
      Keymaster

      Black point compensation means “make the darkest black in the source space also the darkest black in the target space.” If it is off, then you might not get as dark black as you expect/want. So yes, generally I think you do want this turned on.

      I believe it is turned on by default for InDesign conversions.

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