App icon not displaying correctly on macOS 15.7.2

[hazdzz]

Description:
Hi, I'm experiencing an issue where the Sloth.app icon is displaying as a colored grid pattern instead of the proper app icon on external 1080p displays.

Environment:

• macOS version: 15.7.2
• Chip: M1 Pro
• Sloth version: 3.5 (368)

Screenshots:

[sveinbjornt]

Is the icon scrambled like this at all sizes and everywhere in the Finder and Dock UI?

[hazdzz]

Is the icon scrambled like this at all sizes and everywhere in the Finder and Dock UI?

On my external 1080p displays, the small-size icon appears scrambled in Finder and Launchpad, while the normal-size icon displays correctly in the Dock, Finder, and Launchpad.

[sveinbjornt]

Could you do me a favour?

Ctrl-click Sloth.app, select Show Package Contents, then open Contents, then Resources, and open the sloth.icns file in that folder with Preview. Do any of the images appear scrambled in Preview?

[sveinbjornt]

Thank you, but how does Preview show the app's icon file?

What I'm trying to discover is whether this is a Finder bug or a bug in the macOS CoreImage image processing library.

[hazdzz]

[sveinbjornt]

Hmmm.... looks like a Finder bug. Does this persist between restarts? I am not able to reproduce this on macOS 15.7.1. Will upgrade the OS to 15.7.2 to see if this is a regression in the latest OS update.

[hazdzz]

Hmmm.... looks like a Finder bug. Does this persist between restarts? I am not able to reproduce this on macOS 15.7.1. Will upgrade the OS to 15.7.2 to see if this is a regression in the latest OS update.

I rebooted my MacBook Pro, but the problem still exists.

[sveinbjornt]

Upgraded to 15.7.2, unable to reproduce. All PNG forms validated by the spec. This is an Apple bug, not mine. Apparently their PNG decoding library is not following the spec. Closing.

[hazdzz]

Root Cause

The @1x versions of small-size icons in AppIcon.icns are corrupted:

• ✗ icon_16x16.png - displays as colorful mosaic
• ✗ icon_32x32.png - displays as colorful mosaic
• ✓ icon_16x16@2x.png and all larger sizes are fine

This only affects external monitors because Retina displays use the working @2x versions, while external monitors may require the corrupted @1x versions depending on their scaling settings.

Solution

1. Extract the existing iconset:

iconutil -c iconset /path/to/Sloth.app/Contents/Resources/AppIcon.icns -o ~/Desktop/AppIcon.iconset

2. Regenerate the corrupted small icons from a high-resolution source:

cd ~/Desktop/AppIcon.iconset/
sips -z 16 16 icon_512x512@2x.png --out icon_16x16.png
sips -z 32 32 icon_512x512@2x.png --out icon_32x32.png

3. Repackage the iconset:

iconutil -c icns ~/Desktop/AppIcon.iconset -o ~/Desktop/AppIcon.icns

4. Replace the file in the app bundle and clear icon cache:

# Backup original
cp /path/to/Sloth.app/Contents/Resources/AppIcon.icns{,.backup}

# Replace with fixed version
cp ~/Desktop/AppIcon.icns /path/to/Sloth.app/Contents/Resources/AppIcon.icns

# Clear macOS icon cache
sudo rm -rf /Library/Caches/com.apple.iconservices.store
killall Dock

[hazdzz]

Upgraded to 15.7.2, unable to reproduce. All PNG forms validated by the spec. This is an Apple bug, not mine. Apparently their PNG decoding library is not following the spec. Closing.

I found the cause. Please repackage the icon file following the method above, and that should resolve the issue.

[sveinbjornt]

LLM?