Chaos Corona for 3ds Max > [Max] Bug Reporting

Huge bug - double rendertimes with black backdrop

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Pavlov:
Hi,

in Corona we miss a very important feature, which is Unpremultiplied Alpha.
Without it, any compositing operation will have issues.

So we have to use an "old" workaround, which is rendering with black visible backdrop. Anyway, as soon as you try to do it, you will get double rendertimes.
So we have a missing feature and a bug in the unique workaround possible.

Hopefully this will get a fix, it's like that since Corona 8 or so.

Best
Paolo

Aram Avetisyan:
Hi,

Aren't you able to to the premultiplication of the Alpha in the compositing software?
Corona provide the alpha channel data, given you save in the corresponding format, which you can use anyway you want, if the software lets it.

How exactly are you using the black backdrop?
There is no way it should double the render times. You can simply use it as environment overrides, e.g. for direct visibility (background) in the Render Settings > Scene tab.

dj_buckley:

--- Quote from: Aram Avetisyan on 2024-02-05, 10:13:12 ---Hi,

Aren't you able to to the premultiplication of the Alpha in the compositing software?
Corona provide the alpha channel data, given you save in the corresponding format, which you can use anyway you want, if the software lets it.

How exactly are you using the black backdrop?
There is no way it should double the render times. You can simply use it as environment overrides, e.g. for direct visibility (background) in the Render Settings > Scene tab.

--- End quote ---

It absolutely does result in a huge render time increase.  I posted about it back in 2021 https://forum.corona-renderer.com/index.php?topic=34688.msg191184#msg191184

maru:
"Unpremultiplied Alpha" - That's not a Corona/3ds Max feature, but the 2D editor's, right? You can render an image with an HDRI background, or anything else, without using the black background solution, load it in a compositing software, and specify premultiplied/unpremultiplied alpha there. There were many forum threads in the past where we shared how exactly the same data loaded into Photoshop looks "wrong" compared to Fusion or Nuke.

"Scene rendering longer on a black background" - The link points to a thread where the issue was related to using the noise limit. Can you confirm that everything is working as expected with pass or time limit? That is, the render time is higher when using noise limit only, and when using pass limit or time limit, there is no performance drop when using a black background.

dj_buckley:

--- Quote from: maru on 2024-02-05, 17:18:23 ---"Scene rendering longer on a black background" - The link points to a thread where the issue was related to using the noise limit. Can you confirm that everything is working as expected with pass or time limit? That is, the render time is higher when using noise limit only, and when using pass limit or time limit, there is no performance drop when using a black background.

--- End quote ---

Is there any way this behaviour can be improved?  I'd be interested to see, maybe run a poll, on how many users user Noise Limit over the other options.  If I had to guess I'd say noise limit comes out on top by some distance.

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