Compositing / Image Editor Alpha Broken #84386

New Issue

Micah Sibert · 2021-01-04T21:09:03+01:00

Micah Sibert commented

2021-01-04 21:09:03 +01:00

System Information
Operating system: macOS Mojave 10.14.6
Graphics card: Radeon Pro Vega 48

Blender Version
Broken: 2.92.0 Alpha, 1e8f266591, master
Worked: 2.90 Alpha (last one I have available to check)

Short description of error
Image data which should be hidden by alpha is still 99% visible in Image Editor and Compositing view._AlphaTest.blend

Exact steps for others to reproduce the error
Based on the default startup or an attached .blend file (as simple as possible).

Render Scenes
Use Nodes
Modify alpha with method of choice (set alpha, key, cryptomatte)
Connect to viewer node or composite node

**System Information** Operating system: macOS Mojave 10.14.6 Graphics card: Radeon Pro Vega 48 **Blender Version** Broken: 2.92.0 Alpha, 1e8f2665916c, master Worked: 2.90 Alpha (last one I have available to check) **Short description of error** Image data which should be hidden by alpha is still 99% visible in Image Editor and Compositing view.[_AlphaTest.blend](https://archive.blender.org/developer/F9550670/_AlphaTest.blend) ![_AlphaTest_01.jpg](https://archive.blender.org/developer/F9550669/_AlphaTest_01.jpg) **Exact steps for others to reproduce the error** Based on the default startup or an attached .blend file (as simple as possible). - Render Scenes - Use Nodes - Modify alpha with method of choice (set alpha, key, cryptomatte) - Connect to viewer node or composite node

Micah Sibert commented

2021-01-04 21:09:03 +01:00

Added subscriber: @msibert

Robert Guetzkow commented

2021-01-05 13:34:05 +01:00

Added subscriber: @rjg

Robert Guetzkow commented

2021-01-05 13:34:05 +01:00

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

Robert Guetzkow closed this issue

2021-01-05 13:34:05 +01:00

Robert Guetzkow commented

2021-01-05 13:34:05 +01:00

If I'm not mistaken, the result is correct for working with pre-multiplied / associated alpha. By setting the alpha to the matte you're creating an image where some cubes still have their respective RGB values but zero alpha. This is how emissive but fully transparent objects are represented, like e.g. a candle flame.

If you multiply the image with the matte by using a Mix node (set to Multiply) and assign the result to the image sockets of the Composite and Viewer node, you should see the result you're expecting.

If I'm not mistaken, the result is correct for working with pre-multiplied / associated alpha. By setting the alpha to the matte you're creating an image where some cubes still have their respective RGB values but zero alpha. This is how emissive but fully transparent objects are represented, like e.g. a candle flame. If you multiply the image with the matte by using a *Mix* node (set to *Multiply*) and assign the result to the image sockets of the *Composite* and *Viewer* node, you should see the result you're expecting.

Robert Guetzkow commented

2021-01-05 14:19:31 +01:00

Changed status from 'Archived' to: 'Confirmed'

Robert Guetzkow reopened this issue

2021-01-05 14:19:31 +01:00

Robert Guetzkow commented

2021-01-05 14:19:31 +01:00

I just noticed that the image output from the cryptomatte node doesn't zero the RGB values though and that seems to be incorrect.

@Jeroen-Bakker Correct me if I'm wrong, but the cryptomatte node should set RGB and alpha to zero for the selected objects, not just the alpha, correct?

I just noticed that the image output from the cryptomatte node doesn't zero the RGB values though and that seems to be incorrect. @Jeroen-Bakker Correct me if I'm wrong, but the cryptomatte node should set RGB and alpha to zero for the selected objects, not just the alpha, correct?

Robert Guetzkow commented

2021-01-05 14:22:22 +01:00

Added subscriber: @Jeroen-Bakker