PDF CMYK export

[Poussart]

Am using Publisher 1.10.6 on Mac. This has been nagging me :  When exporting for highest PDF CMYK print quality, InDesign has the “convert to destination - preserve numbers” option: linked images that are already in CMYK are not coverted (again). Affinity Publisher does NOT provide this option. What is the preferred procedure? a) link images that are RGB and rely on the pdf export (with the desired overall profile) to do all the conversion or b) link images that have been converted to CMYK within Affinity photo (with the the Document / Convert format / ICC profile function), using the desired profile and rely on the pdf export with the same desired overall profile) not to touch them. I have been completing a book with over 200 photos and have used a combination of a and b. Is tis OK? Thank you for your advice!

[lacerto]

1 hour ago, Poussart said:

a) link images that are RGB and rely on the pdf export (with the desired overall profile) to do all the conversion

I would recommend this. If you have images in RGB, you will always get the optimum conversion, even when doing the late conversion (in context of PDF export). Basically I would never use the late-bound conversion option in Affinity apps because it results in full conversion of all CMYK defined colors, including native K100 like text that you would typically want to keep as K100. All that would become four-color black if you chose to export NOT using the document CMYK.

Having CMYK images placed in Affinity apps easily becomes absurdly complex. First, because images that are handled as documents (like Affinity Photo or Photoshop file formats) will have their native CMYK profiles honored, while non-document images (like JPG and TIFF) will have CMYK profiles assigned as defined in Preferences > Color at the time these files were placed [NOT the document CMYK profile as you might assume]. And secondly, because of version changes: In v1 apps these files could have their CMYK profiles reassigned by refreshing the links in Resource Manager, while in v2 apps they need to be physically removed and placed again (having the correct target profile specified in Preferences > Color).

There is a fundamental difference between Adobe apps (InDesign) and Affinity apps: the former basically always discard CMYK profiles of placed images so the native CMYK values get passed through. Affinity apps always convert them if there is a "conflict". What makes a conflict, may be hard to detect.

Correction: What was stated above is relevant in cases color profile is not embedded within placed CMYK images. If it is, the embedded color profile is honored so the conflict is easy to detect, but not necessarily easy to resolve (to reassign placed images with the new target, to not cause unnecessary recalculation of color values).

[Poussart]

Thank you so much! I have searched in vain for clarity in Affinity documentation on this. This is so useful!. If I may, could you explain what you mean by "the late-bound conversion option in Affinity apps". Does this has anything to do with the "Convert image colour spaces" toggle which is on the "More" Panel of the Export. I assume that this "Convert image colour spaces" should be clicked on so that the RGB images are converted to CMYK and this is my current setting. But with CMYK set for the overall colour space, is'nt this an uncessary repetirion?

[lacerto]

3 hours ago, Poussart said:

"the late-bound conversion option in Affinity apps".

I mean the situation where you specify a color profile in context of exporting to PDF.

If the specified profile is not "Use document profile", all native CMYK color values are recalculated, in addition to placed files with a conflicting profile (I think that in some situations a forced recalculation of CMYK color values can be caused even if specifying explicitly the same color profile the document is using). So the recipe for reassignment and keeping the color values would be using File > Document > Color and changing the CMYK color profile while using the "Assign" option. But that operation does not refresh profile assignments of CMYK images that do not have embedded profiles, nor does it result in marking the CMYK images with conflicting embedded profiles as ones that are non-conflicting and should have their native CMYK values passed through.

3 hours ago, Poussart said:

I assume that this "Convert image colour spaces" should be clicked on so that the RGB images are converted to CMYK and this is my current setting. But with CMYK set for the overall colour space, is'nt this an uncessary repetirion?

Yes, that option is used when wanting to force conversion of placed RGB images to CMYK when exporting to press-related PDF presets that allow RGB images (like PDF/X-3 and PDF/X-4 and any non-PDF/X based export method using PDF version 1.4 or later -- and as Affinity apps do not support version 1.3, this means any non-PDF/X-based export method within Affinity apps). Affinity apps always convert native color values to CMYK [in context of PDF/X methods and when specifying "CMYK" color space], even if the target PDF version allows RGB definitions, and this option does not have effect on that.

[lacerto]

It was late and I was not thinking clearly, so here's a more thorough description on how Affinity apps handle placed CMYK images:

1. If they have embedded color profiles, they are honored (not discarded, as by default when placed e.g. in InDesign). If the profile is in conflict with the profile used at PDF export time (which would normally be the same that is specified for the document), colors of the placed file will be recalculated when exporting to meet the requirements of the target CMYK color space.
2. If they do not have embedded profiles, the "document" kinds of placed files (Photoshop PSD, Adobe Illustrator AI, EPS files, PDF files that are placed to be interpreted) will have the CMYK profile assigned according to the setting that was in force in Preferences > Color at the time the file was placed, and not based on the hosting document color profile.

If you subsequently change the document CMYK color profile, these files will not be updated to refetch their assigned color profile from current preferences. In version 1 apps you could update the profile by "replacing" the placed files (by fetching them again via Resource Manager from the file system). In version 2 apps you need to physically remove the placed file and then place it again.

If the placed files are "non-document" kind (JPG, TIFF) without a profile, they will stay unmanaged, which basically means that they will get the document color space at export time (in a word: will get their native colors passed through). This happens whether the document color space is changed via File > Document Setup > Color (whether by assigning or converting), or whether changing a new color profile at export time (using "late" conversion).

So, to answer to your question, if you have already converted your raster images into the final target CMYK values and want to be sure that those exact values get passed through when you place the file in Publisher, no matter which export CMYK profile is eventually used, save your images in JPG or TIFF format and without a profile (do NOT use Photoshop PSD); or: embed a profile with images that matches the export CMYK profile and make sure that the placed files are up-to-date. To avoid conversion of native CMYK values, do not match the color profile "late" (that is, change the profile at the time of export): even if your placed images with an embedded profile matching the new target would retain their color values, the native CMYK definitions would be converted. There is no late "reassign" option available in Affinity apps (one that "keeps numbers"), so if there is need to reassign and keep the color values, do it via File > Document Setup > Color, using "Assign".

[Poussart]

Thank you SO MUCH again. This is a key consideration for proper colour management in (press ready) PDF export. Affinty should have a Youtube tutorial of this. Glad I was not afraid to ask and that you quickly came to the resccue :-))