Bug Recorder - Case 1423485 - Premultiplied Alpha Bug - PNG and EXR

Hi Guys

Unity 2021.2.1f1+ HDRP 12.1+ with Raytracing (WITH TAA instead of DLSS):
Makes no difference if it's TAA or DLSS

This looks like a bug to me related to pre multiply alpha issue. PNG and EXR results in same issue. You get jaggy alpha edges

I'm rendering out PNG with alpha. I have a Physcial Based Sky as my environment, and on my cam I've set the background to pure black color.

However, my image sequence have LOADS of shimmer/flickering around the outer edges of the CG elements, where the sky touches my cg elements. That same outer edges also appear to have no anti-aliasing. The cg itself is fine and with practically 0 flicker and practically perfect anti-aliasing

Here's a portion of the render at 200%:


and with the alpha:



This is from the EXR, but PNG gives same result. You can clearly see the jaggy edges.

I also tried in Resolve/Fusion, and it looks the same.

 

In resolve with staright alpha:


In resolve with premultiplied alpha:


Clearly there's an issue

@vladala could you take a look for me please

 

I've also tried various AA options, all with same jaggy alpha edge result
DLSS
TAA - Medium
No AA

All the same on alpha edges (of course "inside" the cg parts, the AA is different based on the AA I choose, but on the background alpha edges, its still a mess)

 

Investigating some more, and I wonder perhaps if this could help troubleshoot thigns:

Here I have a custom pass volume, white assigned. Injection point: "BEFORE Post Process"
(things seem fine and I could probably output this and use it as my alpha, but then I have to run the output twice, and over 8000 frames, that could take some time.


Next up, same as above, but injection point: "AFTER Post Process"


Looking at those 2 shots, it feels to me its the wrong way around. I would expect the smoother, correct one to be the AFTER Post process, but from these screenshots, it seems its the wrong way around.

 

Thanks @antoinecharton , looking forward to your findings

 

Any light at the end of the tunnel on this issue @antoinecharton ?
Could you maybe give us the bug number so I can check when it is fixed....

 

Guys, any news on this please or bug number that I can track?

@antoinecharton @vladala @cguertin
@unitybru

 

Thanks @antoinecharton

Any idea if work has begun on attempting to fix it yet?

 

Thanks, looking forward to it

Keep up the good work

 

Tried that, didnt help in my case

 

Sorry for the late reply @antoinecharton
Here's my settings:


And here is the wrong output it produces (PNG file displayed in Photoshop and zoomed 200%):


For giggles:


But output still the same:


But the setting make no difference:

 

(carryin on from previous message due to 5 atachment limit per message)






Unity 2021.2.2f1 with Raytracing, Recorder 4.0.0-pre.2

 

Cam settings:

 

Hmmm @antoinecharton I'm afraid that still doesnt work. It just smudges the heck out of the image, and then the alpha looks exactly the same:

 

Ive now finally submitted a bug report for this @antoinecharton
(Case 1423485) Alpha AA bug against background when Rendering with Recorder

I used a NEW scene using latest Unity 2022.2.0a11 and HDRP and Recorder 4.0.0-pre.4

There is only a cube in the scene and a single tree with grey material assigned.

Here is screenshot from opened in Photoshop, and comped over a red/pink(ish) colour to make the alpha issue more apparent (PNG and EXR tests result in same look)

This is crop of a 4K render with TAA:


And here's one with DLSS instead of the TAA that I used in my bug report. Its slightly better, but still very noticable


And if I switch on Accumulation and set samples to 8, it gets even weirder as now it adds a white edge to the inside LOL

 

Accumulation set to 32 samples (cam using TAA on High Preset)

 

Accumulation set to 128 samples (cam using TAA on High Preset. There is no animation in the scene, not from the cube or the cam, but something weird going on for sure)

 

DLSS on Cam with Accumulation 128. Getting there.But still some weird halo type of white effect on the inside of outer edges:

 

SMAA with 128 Accumulation. Upper edges still have jaggies:

 

I dont want to bother checking with MSAA as I eventually need Raytraxcing/Pathtracxing enabled also and MSAA doesnt work with that

 

EDIT: Added the case number to the thread title
Case 1423485

 

Sooooo, what now?

 

I just noted the "resolution note" for the issue tracker:


Are you kidding me? Do the QA guys have any compositinig experience AT ALL?

Even just the fact that they don't note the correct problem is mind boggling




Can a senior person at Unity, that knows something about compositing, please update the issue with the correct problem, and note that there is no current solution. The issue is present with AND without DLSS so it has nothing to do with DLSS. No matter what AA solution you set, the alpha is totally ignored in terms of AA. I'm not sure how much clearer I should be making my examples.....

@antoinecharton
@markvi
@vladala

 

OK, thanks for checking @The_Island