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authorLibravatarLibravatar Biswakalyan Bhuyan <biswa@surgot.in> 2022-11-13 23:46:45 +0530
committerLibravatarLibravatar Biswakalyan Bhuyan <biswa@surgot.in> 2022-11-13 23:46:45 +0530
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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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