Vector pass not being saved correctly when using the File Output node #101263

New Issue

Mike Pan · 2022-09-22T00:37:39+02:00

Mike Pan commented

2022-09-22 00:37:39 +02:00

System Information
Operating system: Win 10
Graphics card: RTX 3090

Blender Version
Broken: 3.3
Worked: Not sure

Short description of error
According to doc, vector pass is a 4-component vector, but when it's being piped through to a File Node in the compositor, it seems only 3 components are saved. This causes some motion data to be missing in the final multilayer exr.

Exact steps for others to reproduce the error

Open attached file
Render > Animation - it will render 1 frame and save 2 exrs.
1. One using the blender native file output
2. Another using the file Node
Once it's rendered, the compositor should auto update to load these 2 exrs files below. If not, refresh the input nodes.
Check the vectorblured output. They are different.
mblur-bug.blend

**System Information** Operating system: Win 10 Graphics card: RTX 3090 **Blender Version** Broken: 3.3 Worked: Not sure **Short description of error** According to doc, vector pass is a 4-component vector, but when it's being piped through to a File Node in the compositor, it seems only 3 components are saved. This causes some motion data to be missing in the final multilayer exr. **Exact steps for others to reproduce the error** - Open attached file - `Render` > `Animation` - it will render 1 frame and save 2 exrs. 1. One using the blender native file output 2. Another using the file Node - Once it's rendered, the compositor should auto update to load these 2 exrs files below. If not, refresh the input nodes. - Check the vectorblured output. They are different. [mblur-bug.blend](https://archive.blender.org/developer/F13548473/mblur-bug.blend)

Mike Pan commented

2022-09-22 00:37:39 +02:00

Added subscriber: @MikePan

Germano Cavalcante commented

2022-09-23 02:26:17 +02:00

Added subscriber: @mano-wii

Germano Cavalcante commented

2022-09-23 02:26:17 +02:00

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

Germano Cavalcante commented

2022-09-23 02:26:17 +02:00

I can confirm that the Vector input of the File Output node, although receiving a texture with 4 components, only saves 3 components (ignoring what in many cases is considered the Alpha).

I can confirm that the `Vector` input of the `File Output` node, although receiving a texture with 4 components, only saves 3 components (ignoring what in many cases is considered the Alpha).

Philipp Oeser changed title from ~~Vector pass not being saved correctly when using the file Node~~ to Vector pass not being saved correctly when using the File Output node

2022-09-23 11:45:35 +02:00

Lukas Stockner commented

2022-10-15 17:59:43 +02:00

Added subscriber: @LukasStockner

Lukas Stockner commented

2022-10-15 17:59:43 +02:00

The problem here is that the Motion pass is weird in the compositor - the socket has vector type, but it gets converted to a Operation with color-type output.
The File Output node only sees the vector socket type, and therefore also produces an Operation with vector type that writes three channels. Then, the compositor notices that a color-type output is connected to a vector-type input and adds a conversion, which removes the W component.

Unfortunately, I don't see a way for the File Output node to check what the type of the Operation output that it's connected to will be before creating its own Operation. Some ideas:

Somehow disable automatic conversion and handle it in the Operation - not sure how to do that cleanly in code. There is a flag for skipping conversion, but it only appears to apply if both source AND destination want to skip. Not sure why.
Always make vector input sockets report a color-type input operation. That way, the motion pass with go through without conversion, but now real vector passes will get a vector-to-color conversion. Then, check whether a converter was added and export XYZ if yes, XYZW otherwise.

The problem here is that the Motion pass is weird in the compositor - the socket has vector type, but it gets converted to a Operation with color-type output. The File Output node only sees the vector socket type, and therefore also produces an Operation with vector type that writes three channels. Then, the compositor notices that a color-type output is connected to a vector-type input and adds a conversion, which removes the W component. Unfortunately, I don't see a way for the File Output node to check what the type of the Operation output that it's connected to will be before creating its own Operation. Some ideas: - Somehow disable automatic conversion and handle it in the Operation - not sure how to do that cleanly in code. There is a flag for skipping conversion, but it only appears to apply if both source AND destination want to skip. Not sure why. - Always make vector input sockets report a color-type input operation. That way, the motion pass with go through without conversion, but now real vector passes will get a vector-to-color conversion. Then, check whether a converter was added and export XYZ if yes, XYZW otherwise.

Lukas Stockner self-assigned this 2022-10-15 20:05:32 +02:00

Juan Gea commented

2022-10-16 10:10:59 +02:00

Added subscriber: @juang3d

Juan Gea commented

2022-10-16 10:10:59 +02:00

May I propose as a workaround solution, until this is solved, that the user uses a separate RGBA (not sure if we have separate XYZ in the compositor), save each channel separately as a grey channel and the recompose it in the compositing software.

May this work or is there some other caveat in how the vector pass is handled?

May I propose as a workaround solution, until this is solved, that the user uses a separate RGBA (not sure if we have separate XYZ in the compositor), save each channel separately as a grey channel and the recompose it in the compositing software. May this work or is there some other caveat in how the vector pass is handled?

Lukas Stockner commented

2022-10-16 16:14:39 +02:00

There is a Separate XYZ, but it doesn't give you the fourth component (since Vectors aren't supposed to have a fourth component).

You could also send the Motion pass through any color node that doesn't do anything (mix with factor zero, multiply with 1, that sort of thing - or just Separate RGBA+Combine RGBA) and save the result as a RGBA pass. If you then set the Image Input node to Straight alpha, the result will match the native file.

Or just wait for D16257: Fix #101263: Vector pass is missing W channel in File Output node ;)

There is a Separate XYZ, but it doesn't give you the fourth component (since Vectors aren't supposed to have a fourth component). You could also send the Motion pass through any color node that doesn't do anything (mix with factor zero, multiply with 1, that sort of thing - or just Separate RGBA+Combine RGBA) and save the result as a RGBA pass. If you then set the Image Input node to Straight alpha, the result will match the native file. Or just wait for [D16257: Fix #101263: Vector pass is missing W channel in File Output node](https://archive.blender.org/developer/D16257) ;)

Juan Gea commented

2022-10-17 15:52:30 +02:00

Wait is better… as long as you can update to blender 3.4 or 3.3 if this is back ported, but the workaround could be useful for 3.1 or 3.2 users in case this problem exists (I assume it does)

Thanks for the fix!!

Wait is better… as long as you can update to blender 3.4 or 3.3 if this is back ported, but the workaround could be useful for 3.1 or 3.2 users in case this problem exists (I assume it does) Thanks for the fix!!

Philipp Oeser removed the

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Vector pass not being saved correctly when using the File Output node #101263