Looks like the original is an apng: https://en.wikipedia.org/wiki/APNG

According to that spec, the first frame follows the regular png spec, and all the other frames of the animation are stored in private ancillary chunks. Pngtastic looks to have optimized the first frame and thrown all the others away, which seems reasonable to me.

The optimized file shows this output from pngcheck for me:

> 18:04:00 fluxcapacitor:~/Downloads$ pngcheck -v temp.0.2801077039369998-0.3276898964993583elephant.pngout.png 
zlib warning:  different version (expected 1.2.8, using 1.2.11)

File: temp.0.2801077039369998-0.3276898964993583elephant.pngout.png (12008 bytes)
  chunk IHDR at offset 0x0000c, length 13
    480 x 400 image, 32-bit RGB+alpha, non-interlaced
  chunk IDAT at offset 0x00025, length 11951
    zlib: deflated, 32K window, maximum compression
  chunk IEND at offset 0x02ee0, length 0
No errors detected in temp.0.2801077039369998-0.3276898964993583elephant.pngout.png (3 chunks, 98.4% compression).

I imagine the original file might fail in some decoders (ones that don't support apng), but the optimized file should render (first frame only, no animation) in any png decoder. It renders ok for me in Preview.app on the mac and in Chrome.

Well, for example, the decoder Discord uses fails to load to optimized image(and their decoder does not support apng and it renders first frame fine on original). Though the more I think about it, it could be the compressor used. Maybe its the fact the newer zopfli compression may not be supported so it may be a discord bug... even though its first release was 2013...

Odd, I just tried both the images you posted here in Discord and they both seem to work for me.

Could be a Mac versus PC issue in Discord, but doesn't seem to be a pngtastic bug to me, or at least I can't reproduce it.

Should native code be reintroduced as optional(either build-time or run-time setting) until the pure java impl is stable? I plan to pull the last commit where native code was still in use and see if the issue is still present tomorrow. Also, mac 's discord png code works with the image? That is quite interesting.

After testing, native code ran successfully and loaded by discord perfectly.