forked from josch/img2pdf
test.sh: replace imagemagick with custom python script to produce bit-by-bit identical results on all architectures
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#!/usr/bin/env python3
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import sys
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import numpy
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import scipy.signal
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import zlib
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import struct
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def find_closest_palette_color(color, palette):
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if color.ndim == 0:
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idx = (numpy.abs(palette - color)).argmin()
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else:
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# naive distance function by computing the euclidean distance in RGB space
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idx = ((palette - color) ** 2).sum(axis=-1).argmin()
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return palette[idx]
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def floyd_steinberg(img, palette):
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for y in range(img.shape[0]):
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for x in range(img.shape[1]):
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oldpixel = img[y, x]
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newpixel = find_closest_palette_color(oldpixel, palette)
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quant_error = oldpixel - newpixel
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img[y, x] = newpixel
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if x + 1 < img.shape[1]:
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img[y, x + 1] += quant_error * 7 / 16
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if y + 1 < img.shape[0]:
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img[y + 1, x - 1] += quant_error * 3 / 16
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img[y + 1, x] += quant_error * 5 / 16
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if x + 1 < img.shape[1] and y + 1 < img.shape[0]:
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img[y + 1, x + 1] += quant_error * 1 / 16
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return img
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def convolve_rgba(img, kernel):
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return numpy.stack(
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(
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scipy.signal.convolve2d(img[:, :, 0], kernel, "same"),
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scipy.signal.convolve2d(img[:, :, 1], kernel, "same"),
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scipy.signal.convolve2d(img[:, :, 2], kernel, "same"),
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scipy.signal.convolve2d(img[:, :, 3], kernel, "same"),
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),
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axis=-1,
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)
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def rgb2gray(img):
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result = numpy.zeros((60, 60), dtype=numpy.dtype("int64"))
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for y in range(img.shape[0]):
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for x in range(img.shape[1]):
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clin = sum(img[y, x] * [0.2126, 0.7152, 0.0722]) / 0xFFFF
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if clin <= 0.0031308:
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csrgb = 12.92 * clin
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else:
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csrgb = 1.055 * clin ** (1 / 2.4) - 0.055
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result[y, x] = csrgb * 0xFFFF
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return result
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def palettize(img, pal):
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result = numpy.zeros((img.shape[0], img.shape[1]), dtype=numpy.dtype("int64"))
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for y in range(img.shape[0]):
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for x in range(img.shape[1]):
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for i, col in enumerate(pal):
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if numpy.array_equal(img[y, x], col):
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result[y, x] = i
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break
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else:
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raise Exception()
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return result
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def write_png(data, path, bitdepth, colortype, palette=None):
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with open(path, "wb") as f:
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f.write(b"\x89PNG\r\n\x1A\n")
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# PNG image type Colour type Allowed bit depths
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# Greyscale 0 1, 2, 4, 8, 16
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# Truecolour 2 8, 16
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# Indexed-colour 3 1, 2, 4, 8
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# Greyscale with alpha 4 8, 16
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# Truecolour with alpha 6 8, 16
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block = b"IHDR" + struct.pack(
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">IIBBBBB",
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data.shape[1], # width
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data.shape[0], # height
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bitdepth, # bitdepth
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colortype, # colortype
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0, # compression
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0, # filtertype
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0, # interlaced
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)
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f.write(
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struct.pack(">I", len(block) - 4)
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+ block
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+ struct.pack(">I", zlib.crc32(block))
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)
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if palette is not None:
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block = b"PLTE"
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for col in palette:
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block += struct.pack(">BBB", col[0], col[1], col[2])
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f.write(
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struct.pack(">I", len(block) - 4)
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+ block
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+ struct.pack(">I", zlib.crc32(block))
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)
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raw = b""
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for y in range(data.shape[0]):
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raw += b"\0"
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if bitdepth == 16:
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raw += data[y].astype(">u2").tobytes()
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elif bitdepth == 8:
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raw += data[y].astype(">u1").tobytes()
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elif bitdepth in [4, 2, 1]:
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valsperbyte = 8 // bitdepth
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for x in range(0, data.shape[1], valsperbyte):
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val = 0
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for j in range(valsperbyte):
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if x + j >= data.shape[1]:
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break
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val |= (data[y, x + j].astype(">u2") & (2 ** bitdepth - 1)) << (
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(valsperbyte - j - 1) * bitdepth
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)
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raw += struct.pack(">B", val)
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else:
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raise Exception()
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compressed = zlib.compress(raw)
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block = b"IDAT" + compressed
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f.write(
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struct.pack(">I", len(compressed))
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+ block
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+ struct.pack(">I", zlib.crc32(block))
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)
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block = b"IEND"
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f.write(struct.pack(">I", 0) + block + struct.pack(">I", zlib.crc32(block)))
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def main():
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outdir = sys.argv[1]
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# create a 256 color palette by first writing 16 shades of gray
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# and then writing an array of RGB colors with 6, 8 and 5 levels
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# for red, green and blue, respectively
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pal8 = numpy.zeros((256, 3), dtype=numpy.dtype("int64"))
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i = 0
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for gray in range(15, 255, 15):
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pal8[i] = [gray, gray, gray]
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i += 1
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for red in 0, 0x33, 0x66, 0x99, 0xCC, 0xFF:
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for green in 0, 0x24, 0x49, 0x6D, 0x92, 0xB6, 0xDB, 0xFF:
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for blue in 0, 0x40, 0x80, 0xBF, 0xFF:
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pal8[i] = [red, green, blue]
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i += 1
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assert i == 256
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# windows 16 color palette
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pal4 = numpy.array(
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[
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[0x00, 0x00, 0x00],
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[0x80, 0x00, 0x00],
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[0x00, 0x80, 0x00],
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[0x80, 0x80, 0x00],
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[0x00, 0x00, 0x80],
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[0x80, 0x00, 0x80],
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[0x00, 0x80, 0x80],
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[0xC0, 0xC0, 0xC0],
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[0x80, 0x80, 0x80],
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[0xFF, 0x00, 0x00],
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[0x00, 0xFF, 0x00],
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[0xFF, 0x00, 0x00],
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[0x00, 0xFF, 0x00],
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[0xFF, 0x00, 0xFF],
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[0x00, 0xFF, 0x00],
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[0xFF, 0xFF, 0xFF],
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],
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dtype=numpy.dtype("int64"),
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)
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# choose values slightly off red, lime and blue because otherwise
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# imagemagick will classify the image as Depth: 8/1-bit
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pal2 = numpy.array(
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[[0, 0, 0], [0xFE, 0, 0], [0, 0xFE, 0], [0, 0, 0xFE]],
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dtype=numpy.dtype("int64"),
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)
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# don't choose black and white or otherwise imagemagick will classify the
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# image as bilevel with 8/1-bit depth instead of palette with 8-bit color
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# don't choose gray colors or otherwise imagemagick will classify the
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# image as grayscale
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pal1 = numpy.array(
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[[0x01, 0x02, 0x03], [0xFE, 0xFD, 0xFC]], dtype=numpy.dtype("int64")
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)
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# gaussian kernel with sigma=3
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kernel = numpy.array(
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[
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[0.011362, 0.014962, 0.017649, 0.018648, 0.017649, 0.014962, 0.011362],
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[0.014962, 0.019703, 0.02324, 0.024556, 0.02324, 0.019703, 0.014962],
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[0.017649, 0.02324, 0.027413, 0.028964, 0.027413, 0.02324, 0.017649],
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[0.018648, 0.024556, 0.028964, 0.030603, 0.028964, 0.024556, 0.018648],
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[0.017649, 0.02324, 0.027413, 0.028964, 0.027413, 0.02324, 0.017649],
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[0.014962, 0.019703, 0.02324, 0.024556, 0.02324, 0.019703, 0.014962],
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[0.011362, 0.014962, 0.017649, 0.018648, 0.017649, 0.014962, 0.011362],
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],
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numpy.float,
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)
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# constructs a 2D array of a circle with a width of 36
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circle = list()
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offsets_36 = [14, 11, 9, 7, 6, 5, 4, 3, 3, 2, 2, 1, 1, 1, 0, 0, 0, 0]
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for offs in offsets_36 + offsets_36[::-1]:
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circle.append([0] * offs + [1] * (len(offsets_36) - offs) * 2 + [0] * offs)
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alpha = numpy.zeros((60, 60, 4), dtype=numpy.dtype("int64"))
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# draw three circles
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for (xpos, ypos, color) in [
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(12, 3, [0xFFFF, 0, 0, 0xFFFF]),
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(21, 21, [0, 0xFFFF, 0, 0xFFFF]),
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(3, 21, [0, 0, 0xFFFF, 0xFFFF]),
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]:
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for x, row in enumerate(circle):
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for y, pos in enumerate(row):
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if pos:
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alpha[y + ypos, x + xpos] += color
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alpha = numpy.clip(alpha, 0, 0xFFFF)
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alpha = convolve_rgba(alpha, kernel)
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write_png(alpha, outdir + "/alpha.png", 16, 6)
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normal16 = alpha[:, :, 0:3]
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write_png(normal16, outdir + "/normal16.png", 16, 2)
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write_png(normal16 / 0xFFFF * 0xFF, outdir + "/normal.png", 8, 2)
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write_png(0xFF - normal16 / 0xFFFF * 0xFF, outdir + "/inverse.png", 8, 2)
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gray16 = rgb2gray(normal16)
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write_png(gray16, outdir + "/gray16.png", 16, 0)
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write_png(gray16 / 0xFFFF * 0xFF, outdir + "/gray8.png", 8, 0)
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write_png(
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floyd_steinberg(gray16, numpy.arange(16) / 0xF * 0xFFFF) / 0xFFFF * 0xF,
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outdir + "/gray4.png",
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4,
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0,
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)
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write_png(
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floyd_steinberg(gray16, numpy.arange(4) / 0x3 * 0xFFFF) / 0xFFFF * 0x3,
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outdir + "/gray2.png",
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2,
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0,
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)
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write_png(
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floyd_steinberg(gray16, numpy.arange(2) / 0x1 * 0xFFFF) / 0xFFFF * 0x1,
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outdir + "/gray1.png",
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1,
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0,
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)
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write_png(
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palettize(
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floyd_steinberg(normal16, pal8 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal8
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),
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outdir + "/palette8.png",
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8,
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3,
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pal8,
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)
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write_png(
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palettize(
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floyd_steinberg(normal16, pal4 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal4
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),
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outdir + "/palette4.png",
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4,
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3,
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pal4,
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)
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write_png(
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palettize(
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floyd_steinberg(normal16, pal2 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal2
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),
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outdir + "/palette2.png",
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2,
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3,
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pal2,
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)
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write_png(
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palettize(
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floyd_steinberg(normal16, pal1 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal1
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),
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outdir + "/palette1.png",
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1,
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3,
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pal1,
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)
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main()
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