hitherdither

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A package inspired by [1], implementing dithering algorithms that can be used with PIL/Pillow <https://pillow.readthedocs.io/en/3.3.x/>.

Description

This module is a small extension to PIL/Pillow <https://pillow.readthedocs.io/en/3.3.x/>_, 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:

.. code:: python

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 <http://bisqwit.iki.fi/story/howto/dither/jy/#YliluomaSOrderedDitheringAlgorithm 1>_ using a predefined palette:

.. code:: python

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 <http://doc.pytest.org/en/latest/>`_:

.. code:: sh

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

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