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img2pdf/magick.py

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Python
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#!/usr/bin/env python3
import sys
import numpy
import scipy.signal
import zlib
import struct
def find_closest_palette_color(color, palette):
if color.ndim == 0:
idx = (numpy.abs(palette - color)).argmin()
else:
# naive distance function by computing the euclidean distance in RGB space
idx = ((palette - color) ** 2).sum(axis=-1).argmin()
return palette[idx]
def floyd_steinberg(img, palette):
for y in range(img.shape[0]):
for x in range(img.shape[1]):
oldpixel = img[y, x]
newpixel = find_closest_palette_color(oldpixel, palette)
quant_error = oldpixel - newpixel
img[y, x] = newpixel
if x + 1 < img.shape[1]:
img[y, x + 1] += quant_error * 7 / 16
if y + 1 < img.shape[0]:
img[y + 1, x - 1] += quant_error * 3 / 16
img[y + 1, x] += quant_error * 5 / 16
if x + 1 < img.shape[1] and y + 1 < img.shape[0]:
img[y + 1, x + 1] += quant_error * 1 / 16
return img
def convolve_rgba(img, kernel):
return numpy.stack(
(
scipy.signal.convolve2d(img[:, :, 0], kernel, "same"),
scipy.signal.convolve2d(img[:, :, 1], kernel, "same"),
scipy.signal.convolve2d(img[:, :, 2], kernel, "same"),
scipy.signal.convolve2d(img[:, :, 3], kernel, "same"),
),
axis=-1,
)
def rgb2gray(img):
result = numpy.zeros((60, 60), dtype=numpy.dtype("int64"))
for y in range(img.shape[0]):
for x in range(img.shape[1]):
clin = sum(img[y, x] * [0.2126, 0.7152, 0.0722]) / 0xFFFF
if clin <= 0.0031308:
csrgb = 12.92 * clin
else:
csrgb = 1.055 * clin ** (1 / 2.4) - 0.055
result[y, x] = csrgb * 0xFFFF
return result
def palettize(img, pal):
result = numpy.zeros((img.shape[0], img.shape[1]), dtype=numpy.dtype("int64"))
for y in range(img.shape[0]):
for x in range(img.shape[1]):
for i, col in enumerate(pal):
if numpy.array_equal(img[y, x], col):
result[y, x] = i
break
else:
raise Exception()
return result
# we cannot use zlib.compress() because different compressors may compress the
# same data differently, for example by using different optimizations on
# different architectures:
# https://lists.fedoraproject.org/archives/list/devel@lists.fedoraproject.org/thread/R7GD4L5Z6HELCDAL2RDESWR2F3ZXHWVX/
#
# to make the compressed representation of the uncompressed data bit-by-bit
# identical on all platforms we make use of the compression method 0, that is,
# no compression at all :)
def compress(data):
# two-byte zlib header (rfc1950)
# common header for lowest compression level
# bits 0-3: Compression info, base-2 logarithm of the LZ77 window size,
# minus eight -- 7 indicates a 32K window size
# bits 4-7: Compression method -- 8 is deflate
# bits 8-9: Compression level -- 0 is fastest
# bit 10: preset dictionary -- 0 is none
# bits 11-15: check bits so that the 16-bit unsigned integer stored in MSB
# order is a multiple of 31
result = b"\x78\x01"
# content is stored in deflate format (rfc1951)
# maximum chunk size is the largest 16 bit unsigned integer
chunksize = 0xFFFF
for i in range(0, len(data), chunksize):
# bits 0-4 are unused
# bits 5-6 indicate compression method -- 0 is no compression
# bit 7 indicates the last chunk
if i * chunksize < len(data) - chunksize:
result += b"\x00"
else:
# last chunck
result += b"\x01"
chunk = data[i : i + chunksize]
# the chunk length as little endian 16 bit unsigned integer
result += struct.pack("<H", len(chunk))
# the one's complement of the chunk length
# one's complement is all bits inverted which is the result of
# xor with 0xffff for a 16 bit unsigned integer
result += struct.pack("<H", len(chunk) ^ 0xFFFF)
result += chunk
# adler32 checksum of the uncompressed data as big endian 32 bit unsigned
# integer
result += struct.pack(">I", zlib.adler32(data))
return result
def write_png(data, path, bitdepth, colortype, palette=None):
with open(path, "wb") as f:
f.write(b"\x89PNG\r\n\x1A\n")
# PNG image type Colour type Allowed bit depths
# Greyscale 0 1, 2, 4, 8, 16
# Truecolour 2 8, 16
# Indexed-colour 3 1, 2, 4, 8
# Greyscale with alpha 4 8, 16
# Truecolour with alpha 6 8, 16
block = b"IHDR" + struct.pack(
">IIBBBBB",
data.shape[1], # width
data.shape[0], # height
bitdepth, # bitdepth
colortype, # colortype
0, # compression
0, # filtertype
0, # interlaced
)
f.write(
struct.pack(">I", len(block) - 4)
+ block
+ struct.pack(">I", zlib.crc32(block))
)
if palette is not None:
block = b"PLTE"
for col in palette:
block += struct.pack(">BBB", col[0], col[1], col[2])
f.write(
struct.pack(">I", len(block) - 4)
+ block
+ struct.pack(">I", zlib.crc32(block))
)
raw = b""
for y in range(data.shape[0]):
raw += b"\0"
if bitdepth == 16:
raw += data[y].astype(">u2").tobytes()
elif bitdepth == 8:
raw += data[y].astype(">u1").tobytes()
elif bitdepth in [4, 2, 1]:
valsperbyte = 8 // bitdepth
for x in range(0, data.shape[1], valsperbyte):
val = 0
for j in range(valsperbyte):
if x + j >= data.shape[1]:
break
val |= (data[y, x + j].astype(">u2") & (2 ** bitdepth - 1)) << (
(valsperbyte - j - 1) * bitdepth
)
raw += struct.pack(">B", val)
else:
raise Exception()
compressed = compress(raw)
block = b"IDAT" + compressed
f.write(
struct.pack(">I", len(compressed))
+ block
+ struct.pack(">I", zlib.crc32(block))
)
block = b"IEND"
f.write(struct.pack(">I", 0) + block + struct.pack(">I", zlib.crc32(block)))
def main():
outdir = sys.argv[1]
# create a 256 color palette by first writing 16 shades of gray
# and then writing an array of RGB colors with 6, 8 and 5 levels
# for red, green and blue, respectively
pal8 = numpy.zeros((256, 3), dtype=numpy.dtype("int64"))
i = 0
for gray in range(15, 255, 15):
pal8[i] = [gray, gray, gray]
i += 1
for red in 0, 0x33, 0x66, 0x99, 0xCC, 0xFF:
for green in 0, 0x24, 0x49, 0x6D, 0x92, 0xB6, 0xDB, 0xFF:
for blue in 0, 0x40, 0x80, 0xBF, 0xFF:
pal8[i] = [red, green, blue]
i += 1
assert i == 256
# windows 16 color palette
pal4 = numpy.array(
[
[0x00, 0x00, 0x00],
[0x80, 0x00, 0x00],
[0x00, 0x80, 0x00],
[0x80, 0x80, 0x00],
[0x00, 0x00, 0x80],
[0x80, 0x00, 0x80],
[0x00, 0x80, 0x80],
[0xC0, 0xC0, 0xC0],
[0x80, 0x80, 0x80],
[0xFF, 0x00, 0x00],
[0x00, 0xFF, 0x00],
[0xFF, 0x00, 0x00],
[0x00, 0xFF, 0x00],
[0xFF, 0x00, 0xFF],
[0x00, 0xFF, 0x00],
[0xFF, 0xFF, 0xFF],
],
dtype=numpy.dtype("int64"),
)
# choose values slightly off red, lime and blue because otherwise
# imagemagick will classify the image as Depth: 8/1-bit
pal2 = numpy.array(
[[0, 0, 0], [0xFE, 0, 0], [0, 0xFE, 0], [0, 0, 0xFE]],
dtype=numpy.dtype("int64"),
)
# don't choose black and white or otherwise imagemagick will classify the
# image as bilevel with 8/1-bit depth instead of palette with 8-bit color
# don't choose gray colors or otherwise imagemagick will classify the
# image as grayscale
pal1 = numpy.array(
[[0x01, 0x02, 0x03], [0xFE, 0xFD, 0xFC]], dtype=numpy.dtype("int64")
)
# gaussian kernel with sigma=3
kernel = numpy.array(
[
[0.011362, 0.014962, 0.017649, 0.018648, 0.017649, 0.014962, 0.011362],
[0.014962, 0.019703, 0.02324, 0.024556, 0.02324, 0.019703, 0.014962],
[0.017649, 0.02324, 0.027413, 0.028964, 0.027413, 0.02324, 0.017649],
[0.018648, 0.024556, 0.028964, 0.030603, 0.028964, 0.024556, 0.018648],
[0.017649, 0.02324, 0.027413, 0.028964, 0.027413, 0.02324, 0.017649],
[0.014962, 0.019703, 0.02324, 0.024556, 0.02324, 0.019703, 0.014962],
[0.011362, 0.014962, 0.017649, 0.018648, 0.017649, 0.014962, 0.011362],
],
numpy.float,
)
# constructs a 2D array of a circle with a width of 36
circle = list()
offsets_36 = [14, 11, 9, 7, 6, 5, 4, 3, 3, 2, 2, 1, 1, 1, 0, 0, 0, 0]
for offs in offsets_36 + offsets_36[::-1]:
circle.append([0] * offs + [1] * (len(offsets_36) - offs) * 2 + [0] * offs)
alpha = numpy.zeros((60, 60, 4), dtype=numpy.dtype("int64"))
# draw three circles
for (xpos, ypos, color) in [
(12, 3, [0xFFFF, 0, 0, 0xFFFF]),
(21, 21, [0, 0xFFFF, 0, 0xFFFF]),
(3, 21, [0, 0, 0xFFFF, 0xFFFF]),
]:
for x, row in enumerate(circle):
for y, pos in enumerate(row):
if pos:
alpha[y + ypos, x + xpos] += color
alpha = numpy.clip(alpha, 0, 0xFFFF)
alpha = convolve_rgba(alpha, kernel)
write_png(alpha, outdir + "/alpha.png", 16, 6)
normal16 = alpha[:, :, 0:3]
write_png(normal16, outdir + "/normal16.png", 16, 2)
write_png(normal16 / 0xFFFF * 0xFF, outdir + "/normal.png", 8, 2)
write_png(0xFF - normal16 / 0xFFFF * 0xFF, outdir + "/inverse.png", 8, 2)
gray16 = rgb2gray(normal16)
write_png(gray16, outdir + "/gray16.png", 16, 0)
write_png(gray16 / 0xFFFF * 0xFF, outdir + "/gray8.png", 8, 0)
write_png(
floyd_steinberg(gray16, numpy.arange(16) / 0xF * 0xFFFF) / 0xFFFF * 0xF,
outdir + "/gray4.png",
4,
0,
)
write_png(
floyd_steinberg(gray16, numpy.arange(4) / 0x3 * 0xFFFF) / 0xFFFF * 0x3,
outdir + "/gray2.png",
2,
0,
)
write_png(
floyd_steinberg(gray16, numpy.arange(2) / 0x1 * 0xFFFF) / 0xFFFF * 0x1,
outdir + "/gray1.png",
1,
0,
)
write_png(
palettize(
floyd_steinberg(normal16, pal8 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal8
),
outdir + "/palette8.png",
8,
3,
pal8,
)
write_png(
palettize(
floyd_steinberg(normal16, pal4 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal4
),
outdir + "/palette4.png",
4,
3,
pal4,
)
write_png(
palettize(
floyd_steinberg(normal16, pal2 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal2
),
outdir + "/palette2.png",
2,
3,
pal2,
)
write_png(
palettize(
floyd_steinberg(normal16, pal1 * 0xFFFF / 0xFF) / 0xFFFF * 0xFF, pal1
),
outdir + "/palette1.png",
1,
3,
pal1,
)
if __name__ == "__main__":
main()
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