What is png_get_palette_max supposed to do?

I've implemented this in my Perl module:

https://github.com/benkasminbullock/image-png-libpng/blob/master/tmpl/Libpng.xs.tmpl#L393

I wrote a test:

https://github.com/benkasminbullock/image-png-libpng/blob/master/t/get-palette-max.t

My PNG file in the test has a 256 colour palette:

https://github.com/benkasminbullock/image-png-libpng/blob/master/t/tantei-san.png

But the test outputs 0, rather than 256.

What does png_get_palette_max do? The documentation seems to imply it will
return the number of colours in the palette.

I googled for examples of this function but didn't find anything.

_______________________________________________
png-mng-implement mailing list
png-mng-implement-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
https://lists.sourceforge.net/lists/listinfo/png-mng-implement