basicpng

Pure python PNG decoder.

Usage:

from basicpng import PngDecode

# Load PNG
D = PngDecode("./my.png")
# Grab the extreme corner's U8 RGBA values
x = D.w - 1
y = D.h - 1
(r, g, b, a) = D.get(x, y)
print(r, g, b)

What it does:

Parse IHDR, PLTE, IDAT and IEND chunks. Others are ignored entirely
Supports 1-16 bit per channel formats, including indexed color, but 16bits/channel formats get reduced to 8bits/channel
Only depends on the base Python distribution + zlib. There are cases where this is important...

Limitations:

Only progressive scan images are supported. Adam7 is not.
16bits/channel formats get reduced to 8bits/channel.
Transparency is read only from color types 4 and 6, fancy ancillary chunks are ignored.
Generally, no ancillary chunks are processed.
Probably a lot slower than libpng, I didn't even try to put the head-to-head :-)

In case you're wondering how you can generate test images with indexed-color or gray scale, here are the ImageMagick incantations:

convert ref.png -colors 16 -type Palette indexed.png
convert ref.png -colorspace Gray grayscale.png

identify will report the amount of colors and that it has one channel.

alzwded/basicpng

basicpng