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Posted

Hi,

when using a cmyk document, and add a levels adjustment set to RGB, the rendering changes dramatically (loss of contrast), even if the adjustment sliders stay neutral.

This is at least unexpected.

It is somewhat clear that a GRAY/8 adjustment results in gray rendering.

But the rendering difference between RGB, LAB, CMYK are unexpected.

If this is by design, it would be great to get more information how the result gets calculated/ rendered, and what use these mix-color-profile adjustments have I the results are a bit random for regular users.

Video was captured on iPad, same issue on Windows.

 

PS:

Issue happens only for cmyk documents. RGB and LAB seem unaffected.

cmyk doc with levels in rgb bug.afphoto

Mac mini M1 A2348 | MBP M3 

Windows 11 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080

LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 | Dell 27“ 4K

iPad Air Gen 5 (2022) A2589

Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps.

I use iPad screenshots and videos even in the Desktop section of the forum when I expect no relevant difference.

 

  • 1 month later...
  • Staff
Posted

Hi @NotMyFault,

Issue logged to be looked at.

Not sure why it's giving the results it has.  Personally i wouldn't use an RGB Adjustment in a CMYK document but thats just because i've had it drummed into me over the years to stick to one colour space.  

As soon as i get comment from Dev as to whats happening, i'll update here :) 

Posted

To give some background how this is relevant:

James Ritson showed in his tutorials how to use curves or levels adjustment in an RGB document, but set to LAB to adjust the lightness channel non destructively. So this is kind of officially supported and recommended use. And he invited users more than once to experiment with features.
 

I was experimenting with other combinations, e.g.

  • to use non RGB document and RGB levels to knock out RGB channels,
  • to simulate how wide gamut images look in RGB without doing a destructive conversions.

As of today, there is no documentation what these mixed color format adjustments do exactly. They behave at least unexpected and inconsistent. The whole area is a bit confusing:

  • impact (of color format conversion) visible before adjusting nodes, or after adjusting nodes
  • what is the impact of conversion when nodes stay untouched?
  • Additional impact of layer blend mode (which might use HSL or HSV for blending depending on mode, forgot the details)
  • when i raise these points, it is not that i don’t know the basics of layer blending, alpha blending, blend modes etc. It is simply lack of knowledge/ documentation on how Affinity Apps combine these aspects which are non-standard as far as i know, possibly deviate from how PS is handling it (see pass through blend mode), and neither google / wikipedia / Affinity help / Affinity workbook / Affinity forum / Affinity Spotlight / Official tutorials provide a comprehensive answer. I studied lots of available documents, e,g. the official docs from Adobe regarding PS, the svg standard, and all the resources i listed above. There is nothing / nada going into those details
  • So i really hope that Affinity devs open their secret chamber of “design decisions” and make some small talk with (intensely) curious users like @DM1, me and others who try to shed some light into these arcane secrets.

Mac mini M1 A2348 | MBP M3 

Windows 11 - AMD Ryzen 9 5900x - 32 GB RAM - Nvidia GTX 1080

LG34WK950U-W, calibrated to DCI-P3 with LG Calibration Studio / Spider 5 | Dell 27“ 4K

iPad Air Gen 5 (2022) A2589

Special interest into procedural texture filter, edit alpha channel, RGB/16 and RGB/32 color formats, stacking, finding root causes for misbehaving files, finding creative solutions for unsolvable tasks, finding bugs in Apps.

I use iPad screenshots and videos even in the Desktop section of the forum when I expect no relevant difference.

 

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