png2sixel does not work for small png files (~140x165)

[MiroPalmu]

On arch linux with foot version: 1.18.1 +pgo +ime +graphemes -assertions

img2sixel 1.10.3

configured with:
  libcurl: yes
  libpng: no
  libjpeg: no
  gdk-pixbuf2: yes
  GD: no

does not display small png files.

I have three test files with sizes 125x165 (a.png), 138x165 (b.png) and 138x140 (c.png). From these only b.png works. See screenshot below.