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Add support for 16-bit precision JPEG quantization values

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Don't force JPEG quantization to be baseline-compatible

Quantization values will not be limited to values 1..255 and may
be 16 bits if needed. This may cause compatibility issues.
This commit is contained in:
gofr 2020-09-12 20:15:33 +02:00
parent 2e029d9a79
commit 6db0843af4
2 changed files with 14 additions and 13 deletions
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20
src/PIL/JpegImagePlugin.py
View File

@ -36,6 +36,7 @@ import io
import os
import struct
import subprocess
import sys
import tempfile
import warnings
@ -244,15 +245,16 @@ def DQT(self, marker):
n = i16(self.fp.read(2)) - 2
s = ImageFile._safe_read(self.fp, n)
while len(s):
if len(s) < 65:
raise SyntaxError("bad quantization table marker")
v = i8(s[0])
if v // 16 == 0:
self.quantization[v & 15] = array.array("B", s[1:65])
s = s[65:]
else:
return # FIXME: add code to read 16-bit tables!
# raise SyntaxError, "bad quantization table element size"
precision = 1 if (v // 16 == 0) else 2 # in bytes
qt_length = 1 + precision * 64
if len(s) < qt_length:
raise SyntaxError("bad quantization table marker")
data = array.array("B" if precision == 1 else "H", s[1:qt_length])
if sys.byteorder == "little" and precision > 1:
data.byteswap() # the values are always big-endian
self.quantization[v & 15] = data
s = s[qt_length:]
#
@ -683,7 +685,7 @@ def _save(im, fp, filename):
try:
if len(table) != 64:
raise TypeError
table = array.array("B", table)
table = array.array("H", table)
except TypeError as e:
raise ValueError("Invalid quantization table") from e
else:

7
src/libImaging/JpegEncode.c
View File

@ -159,22 +159,21 @@ ImagingJpegEncode(Imaging im, ImagingCodecState state, UINT8* buf, int bytes)
quality = context->quality;
}
for (i = 0; i < context->qtablesLen; i++) {
// TODO: Should add support for none baseline
jpeg_add_quant_table(&context->cinfo, i, &context->qtables[i * DCTSIZE2],
quality, TRUE);
quality, FALSE);
context->cinfo.comp_info[i].quant_tbl_no = i;
last_q = i;
}
if (context->qtablesLen == 1) {
// jpeg_set_defaults created two qtables internally, but we only wanted one.
jpeg_add_quant_table(&context->cinfo, 1, &context->qtables[0],
quality, TRUE);
quality, FALSE);
}
for (i = last_q; i < context->cinfo.num_components; i++) {
context->cinfo.comp_info[i].quant_tbl_no = last_q;
}
} else if (context->quality != -1) {
jpeg_set_quality(&context->cinfo, context->quality, 1);
jpeg_set_quality(&context->cinfo, context->quality, FALSE);
}
/* Set subsampling options */