Pillow/PIL/JpegPresets.py

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"""
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.
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To apply the preset, specify::
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quality="preset_name"
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To apply only the quantization table::
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qtables="preset_name"
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To apply only the subsampling setting::
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subsampling="preset_name"
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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.
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(ref.: https://en.wikipedia.org/wiki/Chroma_subsampling)
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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).
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(ref.: https://en.wikipedia.org/wiki/Quantization_matrix#Quantization_matrices,
https://en.wikipedia.org/wiki/JPEG#Quantization)
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You can get the quantization tables of a JPEG with::
im.quantization
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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:
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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
"""
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presets = {
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'web_low': {'subsampling': 2, # "4:1:1"
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'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]
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]},
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'web_medium': {'subsampling': 2, # "4:1:1"
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'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]
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]},
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'web_high': {'subsampling': 0, # "4:4:4"
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'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],
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[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]
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]},
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'web_very_high': {'subsampling': 0, # "4:4:4"
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'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],
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[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]
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]},
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'web_maximum': {'subsampling': 0, # "4:4:4"
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'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],
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[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]
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]},
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'low': {'subsampling': 2, # "4:1:1"
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'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]
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]},
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'medium': {'subsampling': 2, # "4:1:1"
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'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]
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]},
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'high': {'subsampling': 0, # "4:4:4"
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'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],
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[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]
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]},
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'maximum': {'subsampling': 0, # "4:4:4"
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'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],
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[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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]},
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}