astropulse/hitherdither

Dithering algorithms for arbitrary palettes in PIL

hitherdither

A package inspired by [1], implementing dithering algorithms that can be used with PIL/Pillow.

Description

This module is a small extension to PIL/Pillow, adding a more managable palette object and several dithering algorithms:

• Error diffusion dithering

  • Floyd-Steinberg
  • Jarvis-Judice-Ninke
  • Stucki
  • Burkes
  • Sierra3
  • Sierra2
  • Sierra-2-4A
  • Stevenson-Arce
  • Atkinson

• Standard ordered dithering

  • Bayer matrix
  • Cluster dot matrix
  • Arbitrary square threshold matrix (not implemented yet)

• Yliluoma's ordered dithering (see [1])

  • Algorithm 1
  • Algorithm 2 (not implemented yet)
  • Algorithm 3 (not implemented yet)

The dithering algorithms are applicable for arbitrary palettes and for both RGB and greyscale images.

Installation

pip install git+https://www.github.com/hbldh/hitherdither

Usage

Bayer dithering using a median cut palette:

from PIL import Image
import hitherdither

img = Image.open('image.jpg')
palette = hitherdither.palette.Palette.create_by_median_cut(img)
img_dithered = hitherdither.ordered.bayer.bayer_dithering(
    img, palette, [256/4, 256/4, 256/4], order=8)

Yliluoma's Algorithm 1 using a predefined palette:

from PIL import Image
import hitherdither

palette = hitherdither.palette.Palette(
    [0x080000, 0x201A0B, 0x432817, 0x492910,
     0x234309, 0x5D4F1E, 0x9C6B20, 0xA9220F,
     0x2B347C, 0x2B7409, 0xD0CA40, 0xE8A077,
     0x6A94AB, 0xD5C4B3, 0xFCE76E, 0xFCFAE2]
)

img = Image.open('image.jpg')
img_dithered = hitherdither.ordered.yliluoma.yliluomas_1_ordered_dithering(
    img, palette, order=8)

Tests

Tests can be run with pytest:

hbldh@devbox:~/Repos/hitherdither$ py.test tests
============================= test session starts ==============================
platform linux -- Python 3.5.2, pytest-3.0.2, py-1.4.31, pluggy-0.3.1
rootdir: /home/hbldh/Repos/hitherdither, inifile:
collected 13 items

tests/test_bayer.py ...
tests/test_palette.py ..........

========================== 13 passed in 0.11 seconds ===========================

References

[1]	(1, 2) Joel Yliluoma's arbitrary-palette positional dithering algorithm (http://bisqwit.iki.fi/story/howto/dither/jy/)