Z depth not correct when using a volume shader #98857

New Issue

thierrry kobyleski · 2022-06-13T20:08:12+02:00

2022-06-13 20:08:12 +02:00

System Information
Operating system: Linux-5.13.0-48-generic-x86_64-with-glibc2.31 64 Bits
Graphics card: NVIDIA GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 470.129.06

Blender Version
Broken: version: 3.2.0, branch: master, commit date: 2022-06-08 10:22, hash: e05e1e3691
Worked: (newest version of Blender that worked as expected)

Short description of error
Z depth gives strange "far away values" when using volume shader and thus cant be used for compositing

Exact steps for others to reproduce the error
Just render this blend file
Zmist.blend

**System Information** Operating system: Linux-5.13.0-48-generic-x86_64-with-glibc2.31 64 Bits Graphics card: NVIDIA GeForce GTX 980/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 470.129.06 **Blender Version** Broken: version: 3.2.0, branch: master, commit date: 2022-06-08 10:22, hash: `e05e1e3691` Worked: (newest version of Blender that worked as expected) **Short description of error** Z depth gives strange "far away values" when using volume shader and thus cant be used for compositing ![Screenshot from 2022-06-13 19-54-02.png](https://archive.blender.org/developer/F13157265/Screenshot_from_2022-06-13_19-54-02.png) **Exact steps for others to reproduce the error** Just render this blend file [Zmist.blend](https://archive.blender.org/developer/F13157269/Zmist.blend)

thierrry kobyleski commented

2022-06-13 20:08:12 +02:00

Added subscriber: @thierrykobyleski

Tim commented

2022-06-13 21:36:28 +02:00

Added subscriber: @narcissotto

Tim commented

2022-06-13 21:36:28 +02:00

What is the behavior you expect from this setup? Were you attempting to follow a tutorial? If you could explain what you would like to happen and why, we might be able to find a better method.

Okay, wait, just from context clues and mucking around a bit, I think I found what you were looking to accomplish. The thing that tipped me off was this Note here: "The Z pass only uses one sample. When depth values need to be blended...use the mist pass." Just from a high-level intuition standpoint (I don't claim any knowledge of Z Depth's inner workings), grainy stuff like that can usually be attributed to "undersampling."

When you check the box next to Mist in "View Layer Properties," then back in the Compositing node editor plug Mist directly into Mix's Fac input, it properly mixes the suzanne with the red background. I've attached a file with it "fixed." Hope this was what you're looking for!

Zmist_proper.blend

What is the behavior you expect from this setup? Were you attempting to follow a tutorial? If you could explain what you would *like* to happen and why, we might be able to find a better method. Okay, wait, just from context clues and mucking around a bit, I think I found what you were looking to accomplish. The thing that tipped me off was [this Note here](https://docs.blender.org/manual/en/latest/render/layers/passes.html): "The Z pass **only uses one sample.** When depth values need to be blended...**use the mist pass.**" Just from a high-level intuition standpoint (I don't claim any knowledge of Z Depth's inner workings), grainy stuff like that can usually be attributed to "undersampling." When you check the box next to Mist in "View Layer Properties," then back in the Compositing node editor plug Mist directly into Mix's Fac input, it properly mixes the suzanne with the red background. I've attached a file with it "fixed." Hope this was what you're looking for! [Zmist_proper.blend](https://archive.blender.org/developer/F13157559/Zmist_proper.blend)

thierrry kobyleski commented

2022-06-14 20:14:39 +02:00

I am trying to create some mist with a volume shader for my middleground landscape, while the background is a landscape photograph which I don't want to alter with my volume shader since the photograph already contains its own mist (just a thin haze of air humidity).
With your file Zmist_proper.blend the background can be seen through suzanne.
I made a try using the mist pass distance and adding a background photograph, and a plane for the ground. Here is what I obtain

The new blend file
Zmist_proper_PB.blend

I am trying to create some mist with a volume shader for my middleground landscape, while the background is a landscape photograph which I don't want to alter with my volume shader since the photograph already contains its own mist (just a thin haze of air humidity). With your file Zmist_proper.blend the background can be seen through suzanne. I made a try using the mist pass distance and adding a background photograph, and a plane for the ground. Here is what I obtain ![mistPB.png](https://archive.blender.org/developer/F13164115/mistPB.png) The new blend file [Zmist_proper_PB.blend](https://archive.blender.org/developer/F13164118/Zmist_proper_PB.blend)

thierrry kobyleski commented

2022-06-14 20:40:33 +02:00

New try without film transparency, and with a threshold on the mist pass socket
I obtain what I expected

Here is the blend file
Zmist_proper2.blend
Thank you very much. The problem is solved for me, with this unexpected solution where the mist distance is used to show the background photograph, while the mist is obtained from the volume shader alone.

New try without film transparency, and with a threshold on the mist pass socket I obtain what I expected ![mist.png](https://archive.blender.org/developer/F13164175/mist.png) Here is the blend file [Zmist_proper2.blend](https://archive.blender.org/developer/F13164178/Zmist_proper2.blend) Thank you very much. The problem is solved for me, with this unexpected solution where the mist distance is used to show the background photograph, while the mist is obtained from the volume shader alone.

Germano Cavalcante commented

2022-06-16 01:18:09 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2022-06-16 01:18:09 +02:00

Changed status from 'Needs Triage' to: 'Confirmed'

Germano Cavalcante commented

2022-06-16 01:18:09 +02:00

I'm not sure what the expected depth value should be when there is a volume in the scene, but this randomness doesn't seem to be ideal.
So I'm confirming it as a bug for now.

I'm not sure what the expected depth value should be when there is a volume in the scene, but this randomness doesn't seem to be ideal. So I'm confirming it as a bug for now.

thierrry kobyleski commented

2022-06-16 10:51:45 +02:00

Thanks you. I will try again with "Z value" instead of "mist value" when the bug will be fixed.

Philipp Oeser removed the

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Z depth not correct when using a volume shader #98857