Unable to pack grayscale images into RGBA channels when using A channel #62523

New Issue

Oscar Dario Franco · 2019-03-13T03:57:59+01:00

2019-03-13 03:57:59 +01:00

System Information
Operating system: Win10 64b
Graphics card: Geforce GTX 1060 3GB

Blender Version
Broken: blender-2.80-6b39dc7672eb-win64

Short description of error

I'm trying to use the composite to pack as much grayscale masks into a single image with a combine node to use in a game engine, this technique is widely used to save memory during the game execution.

I have no problem when packing images to RGB channels, but when I try to pack a fourth image using the alpha channel, the R, G and B channels are affected by artifacts caused by the alpha channel, this one (A channel) exports fine though.

Exact steps for others to reproduce the error

I drew this four simple textures and packed into a blend file:

When I pack the first three into an RGBA image, without using the A Channel, everything goes fine: (I'm using unreal engine to see each channel)

But when I try to pack a fourth image using the A channel, the other three get corrupted, the rendered image looks fine, but each channel viewed separately looks bad:

The attached file contains the four images and the compositor setup:

channelsTextures.blend

**System Information** Operating system: Win10 64b Graphics card: Geforce GTX 1060 3GB **Blender Version** Broken: blender-2.80-6b39dc7672eb-win64 **Short description of error** I'm trying to use the composite to pack as much grayscale masks into a single image with a combine node to use in a game engine, this technique is widely used to save memory during the game execution. I have no problem when packing images to RGB channels, but when I try to pack a fourth image using the alpha channel, the R, G and B channels are affected by artifacts caused by the alpha channel, this one (A channel) exports fine though. **Exact steps for others to reproduce the error** I drew this four simple textures and packed into a blend file: ![images.png](https://archive.blender.org/developer/F6812650/images.png) When I pack the first three into an RGBA image, without using the A Channel, everything goes fine: (I'm using unreal engine to see each channel) ![RGB.png](https://archive.blender.org/developer/F6812654/RGB.png) But when I try to pack a fourth image using the A channel, the other three get corrupted, the rendered image looks fine, but each channel viewed separately looks bad: ![RGBA.png](https://archive.blender.org/developer/F6812657/RGBA.png) The attached file contains the four images and the compositor setup: [channelsTextures.blend](https://archive.blender.org/developer/F6812681/channelsTextures.blend)

Oscar Dario Franco commented

2019-03-13 03:57:59 +01:00

Added subscriber: @OscarFranco

Yevgeny Makarov commented

2019-03-13 10:36:26 +01:00

Added subscriber: @jenkm

Yevgeny Makarov commented

2019-03-13 10:36:26 +01:00

After the "Combine RGBA" node you have an image with Premultiplied Alpha.
When you save as PNG, image is converted to Straight Alpha, and the channel values change.

Try to save in the EXR format.

After the "Combine RGBA" node you have an image with Premultiplied Alpha. When you save as PNG, image is converted to Straight Alpha, and the channel values change. Try to save in the EXR format.

Oscar Dario Franco commented

2019-03-13 15:04:44 +01:00

It worked! Thank you very much.

Sorry for posting this problem here, I assumed it was a bug since other software that do similar things, like Substance Designer, allow to do that with PNG and TGA.
Is there any plan for an option that let me control that option for PNG an TGA? maybe an option in the File Output node?

It worked! Thank you very much. Sorry for posting this problem here, I assumed it was a bug since other software that do similar things, like Substance Designer, allow to do that with PNG and TGA. Is there any plan for an option that let me control that option for PNG an TGA? maybe an option in the File Output node?

Sebastian Parborg commented

2019-03-13 15:28:00 +01:00

Added subscriber: @ZedDB

Sebastian Parborg commented

2019-03-13 15:28:00 +01:00

Changed status from 'Open' to: 'Archived'

Sebastian Parborg closed this issue

2019-03-13 15:28:00 +01:00

Sebastian Parborg self-assigned this 2019-03-13 15:28:00 +01:00

Sebastian Parborg commented

2019-03-13 15:28:00 +01:00

Sadly this is not the case. Only exr is able to save lossless atm. This has been requested before but this counts as a feature request and should go to:
https://blender.community/c/rightclickselect/

Sadly this is not the case. Only exr is able to save lossless atm. This has been requested before but this counts as a feature request and should go to: https://blender.community/c/rightclickselect/

Teemu commented

2020-12-01 08:13:06 +01:00

Added subscriber: @TMug

Teemu commented

2020-12-01 08:13:06 +01:00

This kind of feature would be more than useful when dealing with packed game art. Because of this design how the alpha is used, the user is forced to use external program to do the packing or convert the saved EXR to a different format. By being able to do the packing with compositor, this would eliminate the need to open other programs for this kind of work.

Andres Stephens commented

2022-11-08 03:50:36 +01:00

Added subscriber: @AndresStephens

Andres Stephens commented

2022-11-08 03:50:36 +01:00

I tend to agree, this isn't a feature request but a broken feature with some file formats and how they pack channels.

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Unable to pack grayscale images into RGBA channels when using A channel #62523