94 lines
2.4 KiB
Python
94 lines
2.4 KiB
Python
"""Error diffusion dither patterns."""
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import numpy as np
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class DitherPattern:
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PATTERN = None
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ORIGIN = None
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def __init__(self, error_fraction=1.0):
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self.PATTERN *= error_fraction
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class NoDither(DitherPattern):
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"""No dithering."""
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PATTERN = np.array(((0, 0), (0, 0)),
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dtype=np.float32).reshape(2, 2) / np.float32(16)
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ORIGIN = (0, 1)
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class FloydSteinbergDither(DitherPattern):
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"""Floyd-Steinberg dither."""
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# 0 * 7
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# 3 5 1
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PATTERN = np.array(((0, 0, 7), (3, 5, 1)),
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dtype=np.float32).reshape(2, 3) / np.float32(16)
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ORIGIN = (0, 1)
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class FloydSteinbergDither2(DitherPattern):
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"""Floyd-Steinberg dither."""
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# 0 * 7
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# 3 5 1
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PATTERN = np.array(
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((0, 0, 0, 0, 0, 7),
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(3, 5, 1, 0, 0, 0)),
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dtype=np.float32).reshape(2, 6) / np.float32(16)
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ORIGIN = (0, 2)
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class BuckelsDither(DitherPattern):
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"""Default dither from bmp2dhr."""
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# 0 * 2 1
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# 1 2 1 0
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# 0 1 0 0
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PATTERN = np.array(((0, 0, 2, 1), (1, 2, 1, 0), (0, 1, 0, 0)),
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dtype=np.float32).reshape(3, 4) / np.float32(8)
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ORIGIN = (0, 1)
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class JarvisDither(DitherPattern):
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"""Jarvis-Judice-Ninke dithering."""
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# 0 0 X 7 5
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# 3 5 7 5 3
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# 1 3 5 3 1
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PATTERN = np.array(((0, 0, 0, 7, 5), (3, 5, 7, 5, 3), (1, 3, 5, 3, 1)),
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dtype=np.float32).reshape(3, 5) / np.float32(48)
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ORIGIN = (0, 2)
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class JarvisModifiedDither(DitherPattern):
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"""Jarvis dithering, modified to diffuse errors to 4 forward x positions.
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This works well for double hi-res dithering, since the "best" colour
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match to a given pixel may only be accessible up to 4 x-positions further
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on. Standard Jarvis dithering only propagates errors for 2 x-positions
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in the forward direction, which means that errors may have diffused away
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before we get to the pixel that can best take advantage of it.
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"""
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# 0 0 X 7 5
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# 3 5 7 5 3
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# 1 3 5 3 1
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PATTERN = np.array((
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(0, 0, 0, 15, 11, 7, 3),
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(3, 5, 7, 5, 3, 1, 0),
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(1, 3, 5, 3, 1, 0, 0)), dtype=np.float32).reshape(3, 7)
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PATTERN /= np.sum(PATTERN)
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ORIGIN = (0, 2)
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PATTERNS = {
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'floyd': FloydSteinbergDither,
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'floyd2': FloydSteinbergDither2,
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'floyd-steinberg': FloydSteinbergDither,
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'buckels': BuckelsDither,
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'jarvis': JarvisDither,
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'jarvis-mod': JarvisModifiedDither,
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'none': NoDither,
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}
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DEFAULT_PATTERN = 'floyd'
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