| """ |
| 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://web.archive.org/web/20240227115053/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 |
| |
| """ |
|
|
| from __future__ import annotations |
|
|
| |
| presets = { |
| 'web_low': {'subsampling': 2, |
| '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, |
| '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, |
| '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, |
| '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, |
| '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, |
| '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, |
| '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, |
| '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, |
| '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] |
| ]}, |
| } |
| |
|
|
