Affinity Photo 2.4.0 crashes when opening a GIF with only plain text extensions

[JoelOwens]

Affinity Photo 2.4.0 on Windows 10 crashes without an error message when loading a GIF file that only uses plain text extensions.

In practice, the format can hardly be opened by any current program, but these do not crash, but show an error message (such as Photoshop, GIMP, IrfanView, Windows Photo App).

Example: http://cd.textfiles.com/megarom/megarom1/GIF/89AILLUS.GIF

[Hangman]

I'm guessing because the format simply isn't supported though yes, it does indeed instantly crash Affinity apps without any warning...

 

"GIF's Plain Text Extension is a way to define an image composed entirely of text without actually storing the text as a bitmapped image. It defines a rectangular grid of character cells into which text characters of the specified foreground and background colours are placed, starting from the upper left and proceeding left to right and top to bottom; the decoder chooses the font that is the closest match to the specified size.

A casual reading of the GIF specification might suggest that the Plain Text Extension defines a method for cheaply overlaying fixed-width text on top of ordinary pixel data--and, indeed, that was probably the primary motivation behind the extension. But a more careful inspection reveals that the Plain Text Extension is treated as a separate subimage within the GIF stream, on equal terms with any block of bitmap data. It may, in fact, be the only graphic rendering block within the stream. And since PNG images are required to include bitmap data (i.e., IDAT chunks), allowing GIF Plain Text information to be included is perilously close to sanctioning multi-image PNGs. Largely because of this, the gIFt chunk was officially deprecated in October 1998. It is still allowed for backward compatibility (the horses have already left the barn, so to speak), but the current recommendation is that all decoders ignore the chunk and that encoders not write it in the first place. In fact, it is quite possible that no encoder or decoder ever did support gIFt; the Plain Text Extension was rarely used even in GIF's heyday, and even gif2png never supported it."