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Merge pull request #6831 from radarhere/transparency_documentation

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Document "transparency" info key
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mergify[bot] 2022-12-29 00:49:37 +00:00 committed by GitHub
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docs/handbook/concepts.rst
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@ -111,6 +111,18 @@ the file format handler (see the chapter on :ref:`image-file-formats`). Most
handlers add properties to the :py:attr:`~PIL.Image.Image.info` attribute when
loading an image, but ignore it when saving images.
Transparency
------------
If an image does not have an alpha band, transparency may be specified in the
:py:attr:`~PIL.Image.Image.info` attribute with a "transparency" key.
Most of the time, the "transparency" value is a single integer, describing
which pixel value is transparent in a "1", "L", "I" or "P" mode image.
However, PNG images may have three values, one for each channel in an "RGB"
mode image, or can have a byte string for a "P" mode image, to specify the
alpha value for each palette entry.
Orientation
-----------