GIF flattening

[xyz]

XNView 2.50
Some GIFs displayed as GIF flattened.

[XnTriq]

According to XnView, your sample has different DPI values for X and Y (72×18). Adjust zoom if X/Y DPI are different in Tools → Settings… → General → General usually takes care of that. It makes no sense that the sample file is displayed correctly, if this option is turned off

[xyz]

Unchecking this option are fixed problem.

So it's probably a good idea to show a warning to the user or a message in the status bar in this case.
This warning could have a button to invoke the SET DPI dialog box.

[XnTriq]

So it's probably a good idea to show a warning to the user or a message in the status bar in this case.

Yes, I agree.

This warning could have a button to invoke the SET DPI dialog box.

As far as I know, the GIF file format (GIF87a/GIF89a) doesn't support DPI settings.

• GIFLIB documentation: Bits and Bytes
• Adobe Support Community: GIF exporting from Photoshop at low resolution and at a larger size
• Wikipedia: DPI or PPI in digital image files

[xyz]

This warning could have a button to invoke the SET DPI dialog box.

As far as I know, the GIF file format (GIF87a/GIF89a) doesn't support DPI settings.

tl;dr, but Change DPI tool work fine with this file

[XnTriq]

Change DPI tool work fine with this file

Confirmed