forked from josch/img2pdf
magick.py: use our own deflate algo for bit-by-bit reproducible output independent of the compressor used
This commit is contained in:
parent
6da2bc3aee
commit
559d42cd4a
2 changed files with 59 additions and 14 deletions
47
magick.py
47
magick.py
|
@ -71,6 +71,51 @@ def palettize(img, pal):
|
|||
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")
|
||||
|
@ -124,7 +169,7 @@ def write_png(data, path, bitdepth, colortype, palette=None):
|
|||
raw += struct.pack(">B", val)
|
||||
else:
|
||||
raise Exception()
|
||||
compressed = zlib.compress(raw)
|
||||
compressed = compress(raw)
|
||||
block = b"IDAT" + compressed
|
||||
f.write(
|
||||
struct.pack(">I", len(compressed))
|
||||
|
|
26
test.sh
26
test.sh
|
@ -97,19 +97,19 @@ trap error EXIT
|
|||
python3 magick.py "$tempdir"
|
||||
|
||||
cat << END | ( cd "$tempdir"; md5sum --check --status - )
|
||||
7ed200c092c726c68e889514fff0d8f1 alpha.png
|
||||
bf56e00465b98fb738f6edd2c58dac3b gray16.png
|
||||
f93c3e3c11dad3f8c11db4fd2d01c2cc gray1.png
|
||||
d63167c66e8a65bd5c15f68c8d554c48 gray2.png
|
||||
6bceb845d9c9946adad1526954973945 gray4.png
|
||||
7ba8152b9146eb7d9d50529189baf7db gray8.png
|
||||
75130ec7635919e40c7396d45899ddbe inverse.png
|
||||
bd1a2c9f9dfc51a827eafa3877cf7f83 normal16.png
|
||||
329eac79fec2e1bc30d7a50ba2e3f2a5 normal.png
|
||||
9ffd3f592b399f9f9c23892db82369cd palette1.png
|
||||
6d3a39fe5f2efea5975f048d11a5cb02 palette2.png
|
||||
57add39e5c278249b64ab23314a41c39 palette4.png
|
||||
192a3b298d812a156e6f248238d2bb52 palette8.png
|
||||
cc611e80cde3b9b7adb7723801a4e5d4 alpha.png
|
||||
706175887af8ca1a33cfd93449f970df gray16.png
|
||||
198e3333d7dc6158f94d1007e75c5bd3 gray1.png
|
||||
795ff9c5c59cdc95f5a0b9191a7247d9 gray2.png
|
||||
722223ba74be9cba1af4a549076b70d3 gray4.png
|
||||
2320216faa5a10bf0f5f04ebce07f8e1 gray8.png
|
||||
35a47d6ae6de8c9d0b31aa0cda8648f3 inverse.png
|
||||
6ad810399058a87d8145d8d9a7734da5 normal16.png
|
||||
c8d2e1f116f31ecdeae050524efca7b6 normal.png
|
||||
c69edd665ee3546d9eb57fe10cd8095a palette1.png
|
||||
504ecab83662aa2394042a62b1d2eafb palette2.png
|
||||
90d1bbe7b26e210d8846cf8692a98b72 palette4.png
|
||||
50bf09eb3571901f0bf642b9a733038c palette8.png
|
||||
END
|
||||
|
||||
# use img2pdfprog environment variable if it is set
|
||||
|
|
Loading…
Reference in a new issue