simplepng.py

Simple (and inefficient) png manipulation library in a single python3 file.

0. Reads and writes the binary structure of PNG image files in pure python.
1. Can flip/rotate images.
2. Can composite images together using alpha blending.
3. Runs pretty slowly due to some heavy python code running for each pixel.

Status

Still in development.

Example Usage

import simplepng

# read two png files
with open("background.png", "rb") as f:
  image = simplepng.read_png(f, verbose=True)
with open("sprite.png", "rb") as f:
  other_image = simplepng.read_png(f, verbose=True)

# paste the second image onto the first one using alpha blending
image.paste(other_image, 0, 0, 0, 0)

# write the result to a new file
with open("scene.png", "wb") as f:
  simplepng.write_png(f, image)

Running the tests

Run this command in this project's root directory:

python3 test/test.py

Limitations

In memory, this library stores images in RGBA format with 8 bits per channel (32 bits per pixel). When reading 16-bit channels, this library downsamples them to 8-bit channels by simply ignoring the less signficiant byte.

When reading images, only chunk types IHDR, IPLT, tRNS, IDAT, and IEND are recognized; all others are ignored.

When encoding png images, this library makes very simple and naive (i.e. suboptimal) encoding decisions:

• Channel layout is always RGBA with 8 bits per channel (32 bits per pixel).
• Every scanline uses filter type 1 (difference from previous value).

Some experimental evidence using GIMP to re-encode images created with this library shows that this naivety inflates images by about 20% for some images. Of course, this depends heavily on the image being encoded, so YMMV.