Region render passes darker than original

[Joelaff]

You don't happen to have this set to Darken do you ???

[Pixelcon]

Nope it's set to unchanged, but that setting is...scary.

[Joelaff]

This is the post from 2019...a fix was apparently on the way...

https://forums.chaosgroup.com/forum/...ent-brightness

Pretty much what I said above. Cache the Light Cache or use Brute Force.

However, your issue is OUTside the region, which makes me wonder if it isn't what I posted one posting above this one.



I see you already checked this. Darn. Then I am not sure. Could it be some VFB post layers? Like using certain VFB post layers (perhaps the denoiser) cause this? I don't ever do anything in VFB. I save the files out as EXRs and comp elsehwere.

[yavor.rubenov]

Hello,

First of all sorry for the delayed reply.
I see that you say you have the denoiser opacity below 1? Does the issue occur if the denoiser opacity is 1.0 ?

I tried to reproduce the darkening outside of the render region and managed to do this:

I got to here like this:

1. Rendered some image without denoiser
2. Saved it to history
3. Cleared the buffer/Restart Max
4. Loaded the saved image from history
5. Added denoiser
6. Added render region
7. Render

In that case the original image has no denoiser. Adding the denoiser and rendering only a region causes the denoiser element to contain data only inside the region. All pixels outside the region are black. Then trying to blend the denoiser and original image with opacity < 1.0 means that outside the region we are trying to blend the original RGB (loaded from history) and the black pixels from the newly created denoiser element - that just darkens the original image.

Is that something like your case ?

Best regards,
Yavor

[Pixelcon]

Hi Yavor. Thanks for joining

Quick tests:

This error is still persistent when rendered with BF+BF, so the theory that it is related it LC is invalid.

Error is still persistent if the denoiser slider is at 1.

If I disable denoise on one of the affected passes (VrayLighting) the problem goes away. (In the render elements tab)
If I delete the denoiser completely the problem goes away. (In the render elements tab)

edit: This happens only with the default vray denoiser. It happens in a fresh scene (it has some modifications from a vanilla max/vray scene).

[Pixelcon]

Here is a test scene in case you cannot reproduce it.
Render the whole frame, enable region and re-render and it should be evident.

https://drive.google.com/file/d/1Teh...ew?usp=sharing

[yavor.rubenov]

Thanks - it would be easier with a test scene. Will try it and get back to you.

[yavor.rubenov]

With the test scene we managed to reproduce the issue indeed and fix is on the way. It affects render elements that have raw and filter version when using the V-Ray denoiser. (internal ID VMAX-10687)

[Pixelcon]

Thank you my dude

[Joelaff]

So it did turn out to be a VFB layer issue. As soon as you said it was OUTside the region it kinda had to be.

While they work on the fix you could use the standalone denoiser. Render the channels for denoiser and then apply the denoiser after the fact. https://docs.chaosgroup.com/display/VMAX/Denoiser+Tool

We find it to be a bit of a pain in that you need to save out a multi-layered EXR or a vrimg, and those are quite large (esp. for animations). But the standalone denoiser works quite well, again, especially for animations, where it does things you cannot do with the VFB denoiser (compares multiple frames).

I know you don't want workarounds, but the beauty of the forum is that somebody else can find this later and get a workaround and be done.

[Pixelcon]

There are no layers in the VFB so no not really. It must be something going on behind the scenes so to speak.

For now I will just deal with the problem until it is fixed. I just don't have time to add any steps to my workflow right now.

I really appreciate your input however! Thank you!

[Joelaff]

By "Layers" in the VFB I mean anything in the Layers stack in the VFB. I don't know what you call those. Since it says Layers, I call them layers

Denoiser and Lens Effects seem to be special layers, kind of like Adjustment Layers in Photoshop I guess.



The other workaround of course (mentioned early on) is to save your VFB after your main render. Then render the region, and then save that region out and comp them together in Photoshop or Fusion. This also lets you use a feathered mask-- I would render the entire rectangle, not just the selected object, so that you have some room for a feather. Usually this fixes the discrepancies between the different Light Caches mentioned here and in the other thread as well.

Always safest to blend in a patch render.

[yavor.rubenov]

The issue here is in the denoiser itself - in the way it denoises some of the elements - so the standalone denoiser will have the same problem.

[Joelaff]

The issue here is in the denoiser itself - in the way it denoises some of the elements - so the standalone denoiser will have the same problem.

Ah, thanks for the head sup. That sucks.

At least you can comp the region in an external comp program.

[Pixelcon]

Any idea when this is going to be fixed? This is still a big problem for me.