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Merged
aclark4life merged 1 commit into from
Mar 8, 2013
Merged

Adding option to specify/keep quantization tables when saving to JPEG - issue #42 #77

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88 changes: 87 additions & 1 deletion PIL/JpegImagePlugin.py
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Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -36,6 +36,7 @@

import array, struct
from . import Image, ImageFile, _binary
from JpegPresets import presets

i8 = _binary.i8
o8 = _binary.o8
Expand Down Expand Up @@ -416,6 +417,31 @@ def fixup(value):
"YCbCr": "YCbCr",
}

zigzag_index = ( 0, 1, 5, 6, 14, 15, 27, 28,
2, 4, 7, 13, 16, 26, 29, 42,
3, 8, 12, 17, 25, 30, 41, 43,
9, 11, 18, 24, 31, 40, 44, 53,
10, 19, 23, 32, 39, 45, 52, 54,
20, 22, 33, 38, 46, 51, 55, 60,
21, 34, 37, 47, 50, 56, 59, 61,
35, 36, 48, 49, 57, 58, 62, 63)

samplings = {
(1, 1, 1, 1, 1, 1): 0,
(2, 1, 1, 1, 1, 1): 1,
(2, 2, 1, 1, 1, 1): 2,
}

def convert_dict_qtables(qtables):
qtables = [qtables[key] for key in xrange(len(qtables)) if qtables.has_key(key)]
for idx, table in enumerate(qtables):
qtables[idx] = [table[i] for i in zigzag_index]
return qtables

def get_sampling(im):
sampling = im.layer[0][1:3] + im.layer[1][1:3] + im.layer[2][1:3]
return samplings.get(sampling, -1)

def _save(im, fp, filename):

try:
Expand All @@ -427,13 +453,72 @@ def _save(im, fp, filename):

dpi = info.get("dpi", (0, 0))

quality = info.get("quality", 0)
subsampling = info.get("subsampling", -1)
qtables = info.get("qtables")

if quality == "keep":
quality = 0
subsampling = "keep"
qtables = "keep"
elif quality in presets:
preset = presets[quality]
quality = 0
subsampling = preset.get('subsampling', -1)
qtables = preset.get('quantization')
elif not isinstance(quality, int):
raise ValueError("Invalid quality setting")
else:
if subsampling in presets:
subsampling = presets[subsampling].get('subsampling', -1)
if qtables in presets:
qtables = presets[qtables].get('quantization')

if subsampling == "4:4:4":
subsampling = 0
elif subsampling == "4:2:2":
subsampling = 1
elif subsampling == "4:1:1":
subsampling = 2
elif subsampling == "keep":
if im.format != "JPEG":
raise ValueError("Cannot use 'keep' when original image is not a JPEG")
subsampling = get_sampling(im)

def validate_qtables(qtables):
if qtables is None:
return qtables
if isinstance(qtables, basestring):
try:
lines = [int(num) for line in qtables.splitlines()
for num in line.split('#', 1)[0].split()]
except ValueError:
raise ValueError("Invalid quantization table")
else:
qtables = [lines[s:s+64] for s in xrange(0, len(lines), 64)]
if isinstance(qtables, (tuple, list, dict)):
if isinstance(qtables, dict):
qtables = convert_dict_qtables(qtables)
elif isinstance(qtables, tuple):
qtables = list(qtables)
if not (0 < len(qtables) < 5):
raise ValueError("None or too many quantization tables")
for idx, table in enumerate(qtables):
try:
if len(table) != 64:
raise
table = array.array('b', table)
except TypeError:
raise ValueError("Invalid quantization table")
else:
qtables[idx] = list(table)
return qtables

if qtables == "keep":
if im.format != "JPEG":
raise ValueError("Cannot use 'keep' when original image is not a JPEG")
qtables = getattr(im, "quantization", None)
qtables = validate_qtables(qtables)

extra = b""

Expand All @@ -454,7 +539,7 @@ def _save(im, fp, filename):

# get keyword arguments
im.encoderconfig = (
info.get("quality", 0),
quality,
# "progressive" is the official name, but older documentation
# says "progression"
# FIXME: issue a warning if the wrong form is used (post-1.1.7)
Expand All @@ -464,6 +549,7 @@ def _save(im, fp, filename):
info.get("streamtype", 0),
dpi[0], dpi[1],
subsampling,
qtables,
extra,
info.get("exif", b"")
)
Expand Down
250 changes: 250 additions & 0 deletions PIL/JpegPresets.py
View file
Open in desktop
Original file line number Diff line number Diff line change
@@ -0,0 +1,250 @@
"""
JPEG quality settings equivalent to the Photoshop settings.

More presets can be added to the presets dict if needed.

Can be use when saving JPEG file.

To apply the preset, specify:

- quality=preset name

To apply only the quantization table:

- qtables=preset name

To apply only the subsampling setting:

- subsampling=preset name

Example:

im.save("image_name.jpg", quality="web_high")


Subsampling
-----------

Subsampling is the practice of encoding images by implementing less resolution
for chroma information than for luma information.
(ref.: http://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?).

You can get the subsampling of a JPEG with the
`JpegImagePlugin.get_subsampling(im)` function.


Quantization tables
-------------------

They are values use by the DCT (Discrete cosine transform) to remove
*unnecessary* information from the image (the lossy part of the compression).
(ref.: http://en.wikipedia.org/wiki/Quantization_matrix#Quantization_matrices,
http://en.wikipedia.org/wiki/JPEG#Quantization)

You can get the quantization tables of a JPEG with:

im.quantization

This will return a dict with a number of arrays. You can pass this dict directly
as the qtables argument when saving a JPEG.

The tables format between im.quantization and quantization in presets differ in
3 ways:

1. The base container of the preset is a list with sublists instead of dict.
dict[0] -> list[0], dict[1] -> list[1], ...

2. Each table in a preset is a list instead of an array.

3. The zigzag order is remove in the preset (needed by libjpeg >= 6a).

You can convert the dict format to the preset format with the
`JpegImagePlugin.convert_dict_qtables(dict_qtables)` function.

Libjpeg ref.: http://www.jpegcameras.com/libjpeg/libjpeg-3.html

"""

presets = {
'web_low': {'subsampling': 2, # "4:1:1"
'quantization': [
[20, 16, 25, 39, 50, 46, 62, 68,
16, 18, 23, 38, 38, 53, 65, 68,
25, 23, 31, 38, 53, 65, 68, 68,
39, 38, 38, 53, 65, 68, 68, 68,
50, 38, 53, 65, 68, 68, 68, 68,
46, 53, 65, 68, 68, 68, 68, 68,
62, 65, 68, 68, 68, 68, 68, 68,
68, 68, 68, 68, 68, 68, 68, 68],
[21, 25, 32, 38, 54, 68, 68, 68,
25, 28, 24, 38, 54, 68, 68, 68,
32, 24, 32, 43, 66, 68, 68, 68,
38, 38, 43, 53, 68, 68, 68, 68,
54, 54, 66, 68, 68, 68, 68, 68,
68, 68, 68, 68, 68, 68, 68, 68,
68, 68, 68, 68, 68, 68, 68, 68,
68, 68, 68, 68, 68, 68, 68, 68]
]},

'web_medium': {'subsampling': 2, # "4:1:1"
'quantization': [
[16, 11, 11, 16, 23, 27, 31, 30,
11, 12, 12, 15, 20, 23, 23, 30,
11, 12, 13, 16, 23, 26, 35, 47,
16, 15, 16, 23, 26, 37, 47, 64,
23, 20, 23, 26, 39, 51, 64, 64,
27, 23, 26, 37, 51, 64, 64, 64,
31, 23, 35, 47, 64, 64, 64, 64,
30, 30, 47, 64, 64, 64, 64, 64],
[17, 15, 17, 21, 20, 26, 38, 48,
15, 19, 18, 17, 20, 26, 35, 43,
17, 18, 20, 22, 26, 30, 46, 53,
21, 17, 22, 28, 30, 39, 53, 64,
20, 20, 26, 30, 39, 48, 64, 64,
26, 26, 30, 39, 48, 63, 64, 64,
38, 35, 46, 53, 64, 64, 64, 64,
48, 43, 53, 64, 64, 64, 64, 64]
]},

'web_high': {'subsampling': 0, # "4:4:4"
'quantization': [
[ 6, 4, 4, 6, 9, 11, 12, 16,
4, 5, 5, 6, 8, 10, 12, 12,
4, 5, 5, 6, 10, 12, 14, 19,
6, 6, 6, 11, 12, 15, 19, 28,
9, 8, 10, 12, 16, 20, 27, 31,
11, 10, 12, 15, 20, 27, 31, 31,
12, 12, 14, 19, 27, 31, 31, 31,
16, 12, 19, 28, 31, 31, 31, 31],
[ 7, 7, 13, 24, 26, 31, 31, 31,
7, 12, 16, 21, 31, 31, 31, 31,
13, 16, 17, 31, 31, 31, 31, 31,
24, 21, 31, 31, 31, 31, 31, 31,
26, 31, 31, 31, 31, 31, 31, 31,
31, 31, 31, 31, 31, 31, 31, 31,
31, 31, 31, 31, 31, 31, 31, 31,
31, 31, 31, 31, 31, 31, 31, 31]
]},

'web_very_high': {'subsampling': 0, # "4:4:4"
'quantization': [
[ 2, 2, 2, 2, 3, 4, 5, 6,
2, 2, 2, 2, 3, 4, 5, 6,
2, 2, 2, 2, 4, 5, 7, 9,
2, 2, 2, 4, 5, 7, 9, 12,
3, 3, 4, 5, 8, 10, 12, 12,
4, 4, 5, 7, 10, 12, 12, 12,
5, 5, 7, 9, 12, 12, 12, 12,
6, 6, 9, 12, 12, 12, 12, 12],
[ 3, 3, 5, 9, 13, 15, 15, 15,
3, 4, 6, 11, 14, 12, 12, 12,
5, 6, 9, 14, 12, 12, 12, 12,
9, 11, 14, 12, 12, 12, 12, 12,
13, 14, 12, 12, 12, 12, 12, 12,
15, 12, 12, 12, 12, 12, 12, 12,
15, 12, 12, 12, 12, 12, 12, 12,
15, 12, 12, 12, 12, 12, 12, 12]
]},

'web_maximum': {'subsampling': 0, # "4:4:4"
'quantization': [
[ 1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 1,
1, 1, 1, 1, 1, 1, 1, 2,
1, 1, 1, 1, 1, 1, 2, 2,
1, 1, 1, 1, 1, 2, 2, 3,
1, 1, 1, 1, 2, 2, 3, 3,
1, 1, 1, 2, 2, 3, 3, 3,
1, 1, 2, 2, 3, 3, 3, 3],
[ 1, 1, 1, 2, 2, 3, 3, 3,
1, 1, 1, 2, 3, 3, 3, 3,
1, 1, 1, 3, 3, 3, 3, 3,
2, 2, 3, 3, 3, 3, 3, 3,
2, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3,
3, 3, 3, 3, 3, 3, 3, 3]
]},

'low': {'subsampling': 2, # "4:1:1"
'quantization': [
[18, 14, 14, 21, 30, 35, 34, 17,
14, 16, 16, 19, 26, 23, 12, 12,
14, 16, 17, 21, 23, 12, 12, 12,
21, 19, 21, 23, 12, 12, 12, 12,
30, 26, 23, 12, 12, 12, 12, 12,
35, 23, 12, 12, 12, 12, 12, 12,
34, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12],
[20, 19, 22, 27, 20, 20, 17, 17,
19, 25, 23, 14, 14, 12, 12, 12,
22, 23, 14, 14, 12, 12, 12, 12,
27, 14, 14, 12, 12, 12, 12, 12,
20, 14, 12, 12, 12, 12, 12, 12,
20, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12]
]},
'medium': {'subsampling': 2, # "4:1:1"
'quantization': [
[12, 8, 8, 12, 17, 21, 24, 17,
8, 9, 9, 11, 15, 19, 12, 12,
8, 9, 10, 12, 19, 12, 12, 12,
12, 11, 12, 21, 12, 12, 12, 12,
17, 15, 19, 12, 12, 12, 12, 12,
21, 19, 12, 12, 12, 12, 12, 12,
24, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12],
[13, 11, 13, 16, 20, 20, 17, 17,
11, 14, 14, 14, 14, 12, 12, 12,
13, 14, 14, 14, 12, 12, 12, 12,
16, 14, 14, 12, 12, 12, 12, 12,
20, 14, 12, 12, 12, 12, 12, 12,
20, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12]
]},

'high': {'subsampling': 0, # "4:4:4"
'quantization': [
[ 6, 4, 4, 6, 9, 11, 12, 16,
4, 5, 5, 6, 8, 10, 12, 12,
4, 5, 5, 6, 10, 12, 12, 12,
6, 6, 6, 11, 12, 12, 12, 12,
9, 8, 10, 12, 12, 12, 12, 12,
11, 10, 12, 12, 12, 12, 12, 12,
12, 12, 12, 12, 12, 12, 12, 12,
16, 12, 12, 12, 12, 12, 12, 12],
[ 7, 7, 13, 24, 20, 20, 17, 17,
7, 12, 16, 14, 14, 12, 12, 12,
13, 16, 14, 14, 12, 12, 12, 12,
24, 14, 14, 12, 12, 12, 12, 12,
20, 14, 12, 12, 12, 12, 12, 12,
20, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12,
17, 12, 12, 12, 12, 12, 12, 12]
]},

'maximum': {'subsampling': 0, # "4:4:4"
'quantization': [
[ 2, 2, 2, 2, 3, 4, 5, 6,
2, 2, 2, 2, 3, 4, 5, 6,
2, 2, 2, 2, 4, 5, 7, 9,
2, 2, 2, 4, 5, 7, 9, 12,
3, 3, 4, 5, 8, 10, 12, 12,
4, 4, 5, 7, 10, 12, 12, 12,
5, 5, 7, 9, 12, 12, 12, 12,
6, 6, 9, 12, 12, 12, 12, 12],
[ 3, 3, 5, 9, 13, 15, 15, 15,
3, 4, 6, 10, 14, 12, 12, 12,
5, 6, 9, 14, 12, 12, 12, 12,
9, 10, 14, 12, 12, 12, 12, 12,
13, 14, 12, 12, 12, 12, 12, 12,
15, 12, 12, 12, 12, 12, 12, 12,
15, 12, 12, 12, 12, 12, 12, 12,
15, 12, 12, 12, 12, 12, 12, 12]
]},
}
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