248 lines
12 KiB
Python
248 lines
12 KiB
Python
"""
|
||
JPEG quality settings equivalent to the Photoshop settings.
|
||
Can be used when saving JPEG files.
|
||
|
||
The following presets are available by default:
|
||
``web_low``, ``web_medium``, ``web_high``, ``web_very_high``, ``web_maximum``,
|
||
``low``, ``medium``, ``high``, ``maximum``.
|
||
More presets can be added to the :py:data:`presets` dict if needed.
|
||
|
||
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.: 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
|
||
4:2:0.
|
||
|
||
You can get the subsampling of a JPEG with the
|
||
`JpegImagePlugin.get_sampling(im)` function.
|
||
|
||
In JPEG compressed data a JPEG marker is used instead of an EXIF tag.
|
||
(ref.: https://www.exiv2.org/tags.html)
|
||
|
||
|
||
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.: https://en.wikipedia.org/wiki/Quantization_matrix#Quantization_matrices,
|
||
https://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.:
|
||
https://web.archive.org/web/20120328125543/http://www.jpegcameras.com/libjpeg/libjpeg-3.html
|
||
|
||
"""
|
||
|
||
# fmt: off
|
||
presets = {
|
||
'web_low': {'subsampling': 2, # "4:2:0"
|
||
'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, # "4:2:0"
|
||
'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, # "4:2:0"
|
||
'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, # "4:2:0"
|
||
'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]
|
||
]},
|
||
}
|
||
# fmt: on
|