PNGs missing chunks

[D.M.]

Hello! I was trying to rip sprites from a Java mobile game, specifically a Chinese Pokemon clone, but pretty much all the PNGs in the game lack the chunks necessary for it to be read (stuff like the file header, IDAT, etc.). I was wondering how I would go about fixing the PNGs. I included some samples, 2 being some of the few functioning PNGs in the game, and the other 3 being the ones lacking chunks.

[rufaswan]

It is still PNG files, but with PNG header, chunk name + crc32 removed, making everything in fixed order.

For example, "img_220.mid" can be read as:

Code:

00  12 bytes  PNG IHDR header
- 00  4 bytes  width [= 286]
- 04  4 bytes  height [= 153]
- 08  1 byte  bit depth [= 8-bpp]
- 09  1 byte  color type [3=is RGB + has palette]

0c  2 bytes  chunk length
if type has palette , then it is PLTE chunk, then followed by tRNS for Alpha.
After that, the next chunk is IDAT chunk.

You can read more about PNG chunks here:
http://www.libpng.org/pub/png/spec/1.2/PNG-Chunks.html

For example, "img_2.mid" has color type = 6, so it is RGB + has alpha. No palette or PLTE chunk.

You can fix the images by reconstructing all headers back.

Good luck,
- Rufas

[D.M.]

Thanks! I'll check it out and try to do that.