Texture Unpacker: Gray sRGB PNG images display incorrect colors

[badlogic]

Summary

When unpacking a gray sRGB PNG using Spine's Texture Unpacker, the resulting image does not display the intended colors. Converting to color sRGB PNG before unpacking avoids the issue.

User Report

User: https://mail.google.com/mail/u/3/?ogbl#inbox/FMfcgzQfBZmZxXTRZKGnsJWDSNlbkgKg

The user reported that gray sRGB PNG images unpacked with Texture Unpacker don't show correct colors, but color sRGB PNGs work fine.

Technical Analysis

The issue appears to be in how the unpacker loads images:

Current unpacker image loading path:

• SpineUnpacker → gdx TextureAtlas → Texture → Pixmap → stb_image
• stb_image loads pixel data and ignores colorspace metadata

User image loading (in skeleton):

• ImageMonitorTextureLoader → ImageLoader → javax.imageio
• This path handles colorspace correctly

The unpacker uses libgdx's image loading which is less forgiving than the careful loading elsewhere in Spine. We expect atlas images to come from us, but this causes issues with gray sRGB images.

Reproduction

Need repro steps from the user to verify and test a fix.

Potential Fix

Load images differently for the unpacker to handle colorspace metadata properly, similar to how we load user images elsewhere in Spine.

[misaki-eymard]

This issue can be reproduced using the following steps:

1. Open any packed texture atlas page in Photoshop.

2. In Photoshop, go to Image → Mode → Grayscale.

When the warning dialog “Discard color information?” appears, select Discard and proceed.

3. The image will now be converted to grayscale. Export it as a PNG with alpha.

4. Unpack this PNG using Spine 4.3.39-beta.
5. When you inspect the unpacked image, you can see that it appears noticeably lighter and more washed out overall compared to the original.

[NathanSweet]

4.3.56-beta

[NathanSweet]

raptor-gray.zip