Wrong results when passing in a 2-bit png

Optiroc / SuperFamiconv

Flexible and composable tile graphics converter supporting Super Nintendo, Game Boy, Game Boy Color, Game Boy Advance, Mega Drive, PC Engine and WonderSwan formats.

MIT License

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Wrong results when passing in a 2-bit png #6

Closed clbr closed 5 years ago

clbr commented 6 years ago

superfamiconv tiles -DFR -i twobit.png -d test.chr
superfamiconv tiles -n test.chr -o test.png

When twobit.png is 2-bit (as seen by "file", Gimp saves them like that if they have 4 colors), the output is all corrupted. When I convert it to 8-bit, superfamiconv correctly converts it, and test.png looks good.

Optiroc commented 6 years ago

Interesting, may I ask for a 2-bit test file? One possibility is that the error lies with the PNG library (LodePNG) used, in which case I'll:

First, see if bumping it to the latest version fixes the issue
Second, file a bug report

It's not completely unlikely the the error is in my code either, of course! ;) Also, thanks for showing interest in the tool!

clbr commented 6 years ago

PNG_TRANSFORM_PACKING is needed when using the official libpng; that converts 1, 2 and 4-bit images to 8-bit for easier handling. Perhaps lodepng has a similar loading flag.

Sample: https://sub.god.jp/f/yooaen.png

Optiroc commented 6 years ago

There is indeed a bug in my code. LodePNG handles the image just fine (and certain other codepaths in superfamiconv has no problem with it either). Good catch! ;)

clbr commented 6 years ago

Just updating, the same bug happens with 4-bit PNGs.

Optiroc commented 5 years ago

I finally got around to fix this bug (as per commit https://github.com/Optiroc/SuperFamiconv/commit/864d673913d485692f1e80f8321cacc28ff146e8) I don't have any software that can save out a 2/4-bit PNG, so I have only been able to test with the 2-bit image you sent me. I do believe 4-bit images should work too, though.

clbr commented 5 years ago

Gimp is free and available for every OS.

Optiroc commented 5 years ago

I gave it a shot (GIMP-2.10, OSX), but was unable to find these options. With an image in indexed format, but the export PNG dialog will still only list 8/16bpc color pixel formats.

clbr commented 5 years ago

My Gimp is older, 2.6, and doesn't have that dropdown at all. Try the "automatic" option in it anyway, maybe it matches the old behavior.

clbr commented 5 years ago

https://mail.gnome.org/archives/commits-list/2017-January/msg00084.html Yes, the automatic option will do that. For an indexed image with <= 4 colors, 2-bit; for <= 16 colors, 4-bit.

Optiroc commented 5 years ago

I got it working, and fixed 4-bit image loading. Curiously, the LodePNG library did not like the CRC of 4-bit PNGs saved by GIMP. I'm not sure who's in the wrong here, but I disabled the CRC check.