[Publisher] Check CMYK color fill for images

[EEvgeniy]

Good day to you!

It is stated in Printshop rules that:

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For CMYK ... color fill less than 3% is not reproducible, less than 5% is not guaranteed

Where in Publisher I can check that, taking into consideration that all my images are RGB and are converted in CMYK automatically by Publisher?

Thanks in advance!

[v_kyr]

Good question, I would assume that a Preflight possibly will indicate any gltches here, though I'm not sure if always an automatic CMYK conversion would take place for a document at all.

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Preflight:

• Mismatched colour space (RGB)

Further the help system tells that a Soft proof adjustment performs a gammut check ...

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Soft proof adjustment:

• Gamut check—when selected, RGB colours without a CMYK equivalent will display as grey.

... though AFAI interpret it, that doesn't imply an automatic conversion here, just an indication.

When exporting as PDF, a "PDF / X-1a" usually converts all colors to the CMYK target color space. It's normally used when creating print-ready files that do not require additional color conversion. - I would expect that Publisher handles a PDF / X-1a export equally here.

[NotMyFault]

Assuming that we can use these limits (3% and 5%) on cmyk channel bases we could add some suitable adjustments or filters which highlights color values below that threshold.

The best filter would be a procedural texture filter (to check all color channels in one go)

A combination of threshold   and channel mixer adjustment might be suitable, too.

If you make a flattened export, using bend range might work, too.

 This might not work on spot colors.

If you could provide a test document, i will develop the required filters.

[NotMyFault]

Attached you find the tint tester.

 

The tint tester is a procedural texture filter with 2 input parameters: mi and ma (minimum and maximum tint value on a 0-255 scale.

You need to convert the % value into the right scale (*255 / 100), so i have chosen 12 as the round-up of 5% * 255/100.

The tint tester shows all pixels with a CMY value >=1 and <=12 in their original color, all others will become black.. You can adjust the input if required.

If required i can extend this approach to include K (black) channel.

 

The test images shows all 16,7 mio RGB colors converted to CMY(K).

Using the resource manager, you can change the embedded file against you test file.

If required, resize the canvas (currently 4k x 4k)

 

tint tester.afpub

[lacerto]

Basically the profile should be able to take care of conversion so that RGB images get rasterized in a way that produces balanced results. There are of course special cases like below where there might be point in trying to adjust the light end (selectively) to ensure that there is enough coverage to get actually any color printed on the paper and ramps starting at the same spot. But it is difficult and might easily result in compression of tones and too dark light tones.

a) The image below shows profile based conversions of RGB component gradients to CMYK (ISO Coated) using the default Relative Colorimetric intent, and the red lines show where the TAC is about 5% (which for other than CMY still does not mean that halftone pattern gets created and any color really printed). Therefore if light tones are critical it might be best to make the CMYK conversion first and make the necessary adjustments afterwards to see the exact effects ink-wise.      

 

b) Below TAC 5% cut off by stretching the gradients. I doubt that there is a way to do this programmatically, and when color components get thoroughly mixed like in photos component based adjustments become difficult to make, so manually made (areally restricted) level/curves adjustments and selective color adjustments become more relevant.   

 

[EEvgeniy]

I deeply appreciate all your replies, many thanks for your help!

 

On 12/17/2021 at 12:07 AM, v_kyr said:

When exporting as PDF, a "PDF / X-1a" usually converts all colors to the CMYK target color space.

So. For kind of simple tasks would it be correct to handle your document (with all images included) in RGB and convert the final document to CMYK when exporting PDF?