noise in alpha channel

[lacilaci]

I needed to make a render of a furniture piece on a shadowcatcher plane and while the object itself was denoised nicely, shadows of the object weren't.

I am aware that oidn isn't working with transparency but this happens with BCD too.

My workflow was to render with shadowcatcher and transparency and oidn and then composithe alpha AOV of luxcore on denoised result. Again both bcd and oidn will keep object denoised but shadows are noisy.

I talked with Simon on discord about this and he comfirmed that it is the alpha channel itself that is noisy.

So I wanted to ask if it's a normal behavior or a limitation or bug?

The only workaround in this situation is render clean without denoiser but shadows in luxcore are in general extremely slow to converge.

I will create and provide a sample scene later as I'm not at pc during most of weekend.