CMYK PDF export: blending mode (negation) not exporting properly

[nielsh]

I'm running into a huge issue here: I can't get my PDF's to export like they should, not matter what PDF version or options I choose or which Affinity program I use for the export. The only thing that solves it is switching the export to RGB mode, which is simply not an option for print work.

What it should look like:

How it exports:

The big text in the middle is the issue, with blending mode "negation". The other colors are fine, they just look dull because of the CMYK.

The export settings (but like I said, no options outside of switching to RGB export solve the issue for me:

Attached you'll also find a file with the isolated problem.

pdfproblem.afdesign

[NotMyFault]

No PDF expert, but blend mode negation does not work well at all in CMYK.

Assuming you want a rasterized result. 

Instead of blend mode “negate”, i would add a curves adjustment, invert nodes of “master”, and use the text as mask to the adjustment. Exported with “PDF for print” preset looks ok

Another workaround: export as RGB raster image, then open the image, export as PDF.

[nielsh]

Alright, I'll try some other solutions to hopefully get the desired result. Too bad though, it's very confusing that the Affinity apps give no indication whatsoever of the blend modes not being supported in CMYK PDF export, whilst still exporting the file resulting in wildly different results than expected. I also just tried the difference blend mode, which has the same problem, so it's not limited to the negate blend mode.

[nielsh]

Even the invert filter results in the same problem, even the same colors. That's wild.

[NotMyFault]

2 minutes ago, nielsh said:

Alright, I'll try some other solutions to hopefully get the desired result. Too bad though, it's very confusing that the Affinity apps give no indication whatsoever of the blend modes not being supported in CMYK PDF export, whilst still exporting the file resulting in wildly different results than expected. I also just tried the difference blend mode, which has the same problem, so it's not limited to the negate blend mode.

Affinity unfortunately has no airbags or seatbelts.

CMYK reacts allergic to most adjustments, filters, and certain blend modes. Affinity assumes users know what there are doing, and allows using functionality not suited. Even worse, there are many UI elements which are totally useless (non working) in specific situations, like blend modes for mask layers. 
 

But tgis great community is always ready to help you out 😎

[NotMyFault]

44 minutes ago, nielsh said:

Even the invert filter results in the same problem, even the same colors. That's wild.

Invert does not work in CMYK - technically it works, but the inherent redundancy of 4 color channels and subtractive color model gives surprising and unusable results. This is unrelated to Affinity apps, its a principle issue.

 

Simple example:

• Invert 100 / 0 / 0 / 0 (pure cyan)
• result 0 / 100 / 100 / 100 (kind of red, but black oversteers all colours) 

So invert only works if you eliminate  K from the equation

• convert CMYK to CMY, (pseudo formula CMY = CMY + K)
• invert CMY, (CMY = 1-CMY)
• convert again to CMYK (K=min(CMY); CMY=CMY-K

The Affinity implementation "blindly" inverts all channels individually without "K-removal"