Display warning when exporting RGBA using PNG. #93030

New Issue

Jeroen Bakker · 2021-11-12T08:39:40+01:00

Jeroen Bakker commented

2021-11-12 08:39:40 +01:00

Related to #81390.

When exporting a render to RGBA PNG the alpha isn't correct. The issue is related to the different color spaces and PNG (sRGB) not supporting pure emissive colors. We currently don't show a message to the user explaining that it could result into artifacts.

This task would be to add a message when user selects this combination. in the export panel. Or when saving an image that isn't sRGB encoded, using these settings.

Message still needs to be approved:
Saving/Exporting non sRGB but transparent images to PNG creates alpha differences. With a warning icon.

Related to #81390. When exporting a render to RGBA PNG the alpha isn't correct. The issue is related to the different color spaces and PNG (sRGB) not supporting pure emissive colors. We currently don't show a message to the user explaining that it could result into artifacts. This task would be to add a message when user selects this combination. in the export panel. Or when saving an image that isn't sRGB encoded, using these settings. Message still needs to be approved: `Saving/Exporting non sRGB but transparent images to PNG creates alpha differences.` With a warning icon.

Jeroen Bakker commented

2021-11-12 08:39:40 +01:00

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

Jeroen Bakker commented

2021-11-12 08:39:40 +01:00

Added subscriber: @Jeroen-Bakker

Brecht Van Lommel commented

2021-11-12 12:55:26 +01:00

Added subscriber: @brecht

Brecht Van Lommel commented

2021-11-12 12:55:26 +01:00

I'm not sure if this is actually helpful to users. At a minimum it would need to be specific to the case where you are exporting pixels with zero alpha and non-zero RGB, since it works fine in most cases. But even then what is the user supposed to do with this information?

Aaron Carlisle commented

2021-11-12 13:55:34 +01:00

Added subscriber: @Blendify

Aaron Carlisle commented

2021-11-12 13:55:34 +01:00

I would suggest to include a recommended file format that won't exhibit the issue in the message.

Brecht Van Lommel commented

2021-11-12 14:03:03 +01:00

The problem is that this is not really about the file format, there isn't an alternative file format that you can use for the same purpose. The one that works correctly is OpenEXR, but the point of saving as PNG is to be able to use the image for the web or some other image or video editing app that works with unassociated alpha and can't handle this type of emissive image content well.

What you really want is to save the image as unassociated alpha, but with some heuristic to preserve the colors as well as possible even if it can't be perfect. Not to switch to another file format.

The problem is that this is not really about the file format, there isn't an alternative file format that you can use for the same purpose. The one that works correctly is OpenEXR, but the point of saving as PNG is to be able to use the image for the web or some other image or video editing app that works with unassociated alpha and can't handle this type of emissive image content well. What you really want is to save the image as unassociated alpha, but with some heuristic to preserve the colors as well as possible even if it can't be perfect. Not to switch to another file format.

Paul Larson commented

2021-11-13 00:23:26 +01:00

Added subscriber: @GeorgiaPacific

Yuchen Wen commented

2021-11-25 10:50:59 +01:00

Added subscriber: @ksar

Yuchen Wen commented

2021-11-28 16:22:24 +01:00

Hi there, I’m pretty new to this community, but I'd like to try this one.

Yuchen Wen commented

2021-11-28 16:32:46 +01:00

Oh, I didn't see the Good First Issue is removed. I will try another issue.

Yevgeny Makarov commented

2021-11-28 19:31:29 +01:00

Added subscriber: @jenkm

Yevgeny Makarov commented

2021-11-28 19:31:29 +01:00

I don't think any special message is needed here, you just need to use "Export" instead of "Save As" for formats that do not fully support the current image.

It might be useful to have some kind of "straight alpha preview" toggle. You convert the image to unassociated alpha and compose with a checkerboard, so that the user will see what he gets outside of Blender. It's also possible to highlight problematic (zero alpha and non-zero RGB) areas.

I've seen your attempts to add some alpha while converting, but you also need to adjust the color itself, and you can do it for areas with zero alpha, but where the emissive colors is overlaid on a translucent object it seems nothing can be done. Or, for example, on the edge with anti-aliasing.

Any conversion attempts with artifacts will still look like a bug. Or it will even be worse if the user does not immediately notice these artifacts and uses this image somewhere.

I don't think any special message is needed here, you just need to use "Export" instead of "Save As" for formats that do not fully support the current image. It might be useful to have some kind of "straight alpha preview" toggle. You convert the image to unassociated alpha and compose with a checkerboard, so that the user will see what he gets outside of Blender. It's also possible to highlight problematic (zero alpha and non-zero RGB) areas. I've seen your attempts to add some alpha while converting, but you also need to adjust the color itself, and you can do it for areas with zero alpha, but where the emissive colors is overlaid on a translucent object it seems nothing can be done. Or, for example, on the edge with anti-aliasing. Any conversion attempts with artifacts will still look like a bug. Or it will even be worse if the user does not immediately notice these artifacts and uses this image somewhere.

Philipp Oeser removed the

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Display warning when exporting RGBA using PNG. #93030