RGB32 merge visible dithers to 8-bit color depth

[NotMyFault]

Hi,

i would expect all tools working in RGB32 / HDR mode to deliver 32 bit color results, or at least 16 bit.

It seems merge visible reduces to 8-bit color depth, which is not expected.

When using RGB32 with a HDR capable display, i can positively check that  10 bit (1024) grey values are displayed.

• Have a look zommend in to 800%  or more.
• Look in the area bewteen gradient and black rectangle, left from red box, between "unlimited" and "256".
• The gradient has 4 vertical areas:
• top: original
• below: 3 posterized boxes to 256/128/64 levels to make simulated / real banding visible.
• However, when you "merge visible", the merged pixel layer is ditherd and reduced to 8 bit color depth.
• To reproduce, you need a "real" HDR 10-bit capable display (real 10-bit, 8+2 with dithering may show wrong results).
• In perfomance settings, dither gradient must be un-checked.

10 bit before merge:

8 bit after merge visible:

 

levels.afphoto

[NotMyFault]

I've recorded a video to explain the issue.Please excuse for some noise from the mouse, and my bad english.

 

Edited June 18, 2023 by NotMyFault
Video deleted due to quota exceeded

[lepr]

 

On 2/15/2021 at 4:34 PM, NotMyFault said:

i would expect all tools working in RGB32 / HDR mode to deliver 32 bit color results, or at least 16 bit.

It seems merge visible reduces to 8-bit color depth, which is not expected.

You've arrived at a false conclusion. Affinity does not reduce bit depth when merging. You are seeing a problem that is specific to rasterised gradients because merging involves rasterising vector objects.

Currently, and for years, when Affinity rasterises a vector gradient, it applies dither appropriate for an 8 bits per channel image, regardless of the bit depth of the document. Several of us have requested that the dither be made optional and controllable instead of being forced on us. (Don't hold your breath waiting for options to be provided, though.)

There is a trick to prevent the dither. If a vector gradient is enclosed in a Group object that has a Layer Effect applied, then the app neglects to apply dither when rasterising the gradient. The Layer Effect can be invisible, such as a zero opacity Colour Overlay, so that it produces no unwanted side effect. The Group can enclose the whole document to prevent all vector gradients becoming dithered when rasterising.

 

[NotMyFault]

Thank you anon2 for this explanation. I will add my vote to the feature request.

Issue can be closed.