Frame buffer color banding

[Micha]

No big issue since the saved files to the hard disk are clean - the framebuffer shows a color banding.

-Micha

[nikoleta.garkova]

Hi Micha,

Does this happen in a specific scenario - i.e., on a particular monitor you're using, via remote connections, or only on specific materials etc.?
We've not been able to reproduce such behavior, so maybe some further notes could help us if you've noticed any patterns.

[Micha]

I found the reason - it's caused by the curve editor. Attached a test file.

[Micha]

If I use the function "copy current channel to clipboard" than the banding is copied also.

[Micha]

Any feedback about this issue?

[yavor.rubenov]

Hello,

Sorry for the delayed reply. The VFB displays colors in 8bit and does no color dithering at all - both of those can cause visible banding. It has been on the TODO list to experiment both with more bits per pixel and some dithering - but it is quite a bit down in the list..

Best regards,
Yavor

[Micha]

Oh, 8bit is quite limited and it's a pity that it doesn't work like at the frame buffer at the version (VfR4) before. Could it be possible at least that "copy current channel to clipboard" is using the same quality like the saved output?

[yavor.rubenov]

Both the old frame buffer and the new frame buffer use the same code for that part - so no change there.
Copy to clipboard uses some of the OS functionalities to do the copying and it must provide data that other softwares can understand - so it is also limited.

[Micha]

Something must be different and I hope it's a bug which can be easy fixed.

Here a simple test - a point light over a plane - VfR4 vs. VfR5.

[yavor.rubenov]

Ahaa - it's actually an issue in VfR4
When applying the curve correction for display we use a faster cached version of the curve that has limited precision. The bug in VfR4 was that this cache was mistakenly very big which made it kind of pointless. In VfR5 we fixed that issue and now the curve correction is faster for display.

The original image you've sent is very dark (values like 0.009 - 0.09) so the limited precision of the curve for display leads to those visible banding artifacts.

That does not affect saving to file as we use the full curve calculation there.

[Micha]

My example shows an extreme curve correction for better viewing the issue here. But I have seen the banding during projects too.

The problem is that I see the error at the VfR5 framebuffer, but not at VfR4. I can't copy my last rendering per "copy current channel to clipboard" to Photoshop anymore, the banding error is copied too. So, the good old workflow is broken at VfR5 and the display quality looks bad.

[yavor.rubenov]

We'll do some experiments.