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- """
- 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
- :func:`.JpegImagePlugin.get_sampling` function.
-
- In JPEG compressed data a JPEG marker is used instead of an EXIF tag.
- (ref.: https://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 lists. You can pass this dict
- directly as the qtables argument when saving a JPEG.
-
- The quantization table format in presets is a list with sublists. These formats
- are interchangeable.
-
- 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
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