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Fix wrong formula for subsampling=2 while JPEG saving

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This commit is contained in:
Alexander 2017-08-27 20:03:36 +03:00
parent c7136f7ff8
commit 4d56db3a34
5 changed files with 15 additions and 9 deletions
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4
PIL/JpegImagePlugin.py
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@ -635,7 +635,11 @@ def _save(im, fp, filename):
subsampling = 0
elif subsampling == "4:2:2":
subsampling = 1
elif subsampling == "4:2:0":
subsampling = 2
elif subsampling == "4:1:1":
# For compatibility. Before Pillow 4.3, 4:1:1 actually meant 4:2:0.
# Set 4:2:0 if someone is still using that value.
subsampling = 2
elif subsampling == "keep":
if im.format != "JPEG":

10
PIL/JpegPresets.py
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@ -30,7 +30,7 @@ for chroma information than for luma information.
(ref.: https://en.wikipedia.org/wiki/Chroma_subsampling)
Possible subsampling values are 0, 1 and 2 that correspond to 4:4:4, 4:2:2 and
4:1:1 (or 4:2:0?).
4:2:0.
You can get the subsampling of a JPEG with the
`JpegImagePlugin.get_subsampling(im)` function.
@ -67,7 +67,7 @@ Libjpeg ref.: https://web.archive.org/web/20120328125543/http://www.jpegcameras.
"""
presets = {
'web_low': {'subsampling': 2, # "4:1:1"
'web_low': {'subsampling': 2, # "4:2:0"
'quantization': [
[20, 16, 25, 39, 50, 46, 62, 68,
16, 18, 23, 38, 38, 53, 65, 68,
@ -86,7 +86,7 @@ presets = {
68, 68, 68, 68, 68, 68, 68, 68,
68, 68, 68, 68, 68, 68, 68, 68]
]},
'web_medium': {'subsampling': 2, # "4:1:1"
'web_medium': {'subsampling': 2, # "4:2:0"
'quantization': [
[16, 11, 11, 16, 23, 27, 31, 30,
11, 12, 12, 15, 20, 23, 23, 30,
@ -162,7 +162,7 @@ presets = {
3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3]
]},
'low': {'subsampling': 2, # "4:1:1"
'low': {'subsampling': 2, # "4:2:0"
'quantization': [
[18, 14, 14, 21, 30, 35, 34, 17,
14, 16, 16, 19, 26, 23, 12, 12,
@ -181,7 +181,7 @@ presets = {
17, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12]
]},
'medium': {'subsampling': 2, # "4:1:1"
'medium': {'subsampling': 2, # "4:2:0"
'quantization': [
[12, 8, 8, 12, 17, 21, 24, 17,
8, 9, 9, 11, 15, 19, 12, 12,

4
Tests/test_file_jpeg.py
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@ -299,7 +299,7 @@ class TestFileJpeg(PillowTestCase):
self.assertEqual(getsampling(im), (1, 1, 1, 1, 1, 1))
im = self.roundtrip(hopper(), subsampling=1) # 4:2:2
self.assertEqual(getsampling(im), (2, 1, 1, 1, 1, 1))
im = self.roundtrip(hopper(), subsampling=2) # 4:1:1
im = self.roundtrip(hopper(), subsampling=2) # 4:2:0
self.assertEqual(getsampling(im), (2, 2, 1, 1, 1, 1))
im = self.roundtrip(hopper(), subsampling=3) # default (undefined)
self.assertEqual(getsampling(im), (2, 2, 1, 1, 1, 1))
@ -308,6 +308,8 @@ class TestFileJpeg(PillowTestCase):
self.assertEqual(getsampling(im), (1, 1, 1, 1, 1, 1))
im = self.roundtrip(hopper(), subsampling="4:2:2")
self.assertEqual(getsampling(im), (2, 1, 1, 1, 1, 1))
im = self.roundtrip(hopper(), subsampling="4:2:0")
self.assertEqual(getsampling(im), (2, 2, 1, 1, 1, 1))
im = self.roundtrip(hopper(), subsampling="4:1:1")
self.assertEqual(getsampling(im), (2, 2, 1, 1, 1, 1))

4
docs/handbook/image-file-formats.rst
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@ -275,11 +275,11 @@ The :py:meth:`~PIL.Image.Image.save` method supports the following options:
If present, sets the subsampling for the encoder.
* ``keep``: Only valid for JPEG files, will retain the original image setting.
* ``4:4:4``, ``4:2:2``, ``4:1:1``: Specific sampling values
* ``4:4:4``, ``4:2:2``, ``4:2:0``: Specific sampling values
* ``-1``: equivalent to ``keep``
* ``0``: equivalent to ``4:4:4``
* ``1``: equivalent to ``4:2:2``
* ``2``: equivalent to ``4:1:1``
* ``2``: equivalent to ``4:2:0``
**qtables**
If present, sets the qtables for the encoder. This is listed as an

2
libImaging/JpegEncode.c
View File

@ -194,7 +194,7 @@ ImagingJpegEncode(Imaging im, ImagingCodecState state, UINT8* buf, int bytes)
context->cinfo.comp_info[2].v_samp_factor = 1;
break;
}
case 2: /* 2x2, 1x1, 1x1 (4:1:1) : High */
case 2: /* 2x2, 1x1, 1x1 (4:2:0) : High */
{
context->cinfo.comp_info[0].h_samp_factor = 2;
context->cinfo.comp_info[0].v_samp_factor = 2;