Exporting sprite sheet - libpng: Wrote palette index exceeding num_palette

[pseiler]

LibreSprite version

Version 1.0 (AppImage)

Describe the bug

When I try to export a spritesheet, I get the following error:

libpng: Wrote palette index exceeding num_palette
Error saving frame 1 in the file "/home/user/tux.png"

To Reproduce

Expected behaviour

Download this libresprite file here.

OS/Hardware

• Operative System: openSUSE 15.3 x86_64
• CPU: some Intel i5

Additional context

Aseprite seems to have this bug already fixed.
aseprite/aseprite#2842

[tbsp]

I can reproduce this error consistently with the following steps:

• Create a new indexed image, white background
• Load the preset a64 palette (any palette will likely do, though I haven't tried them all)
• Save the image as a png, error occurs

The problem appears to be the image is filled with an out-of-range palette index (but looks like it's full of index 0). Filling the entire canvas with the paint bucket before doing anything else will clear out the out-of-range color and prevent the error. If something is already drawn the magic wand tool is able to distinguish the color and select it, to identify areas to fill with a valid color.