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Document APNG support

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Peter Rowlands 2019-11-29 16:41:23 +09:00 committed by Andrew Murray
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docs/handbook/image-file-formats.rst
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@ -551,6 +551,119 @@ The :py:meth:`~PIL.Image.Image.save` method supports the following options:
library before building the Python Imaging Library. See the `installation
documentation <../installation.html>`_ for details.
APNG sequences
~~~~~~~~~~~~~~~~~
The PNG loader includes limited support for reading and writing APNG files.
When an APNG file is loaded, :py:meth:`~PIL.ImageFile.ImageFile.get_format_mimetype`
will return ``"image/apng"``, and the :py:attr:`~PIL.Image.Image.is_animated` property
will be ``True`` (even for single frame APNG files).
The :py:meth:`~PIL.Image.Image.seek` and :py:meth:`~PIL.Image.Image.tell` methods
are supported.
``im.seek()`` raises an :py:exc:`EOFError` if you try to seek after the last frame.
The following :py:attr:`~PIL.Image.Image.info` properties will be set for APNG frames,
where applicable:
**default_image**
Specifies whether or not this APNG file contains a separate default image,
which is not a part of the actual APNG animation.
When an APNG file contains a default image, the initially loaded image (i.e.
the result of ``seek(0)``) will be the default image.
To account for the presence of the default image, the
py:attr:`~PIL.Image.Image.n_frames` property will be set to ``frame_count + 1``,
where ``frame_count`` is the actual APNG animation frame count.
To load the first APNG animation frame, ``seek(1)`` must be called.
* ``True`` - The APNG contains default image, which is not an animation frame.
* ``False`` - The APNG does not contain a default image. The ``n_frames`` property
will be set to the actual APNG animation frame count.
The initially loaded image (i.e. ``seek(0)``) will be the first APNG animation
frame.
**loop**
The number of times to loop this APNG, 0 indicates infinite looping.
**duration**
The time to display this APNG frame (in milliseconds).
.. note::
The APNG loader returns images the same size as the APNG file's logical screen size.
The returned image contains the pixel data for a given frame, after applying
any APNG frame disposal and frame blend operations (i.e. it contains what a web
browser would render for this frame - the composite of all previous frames and this
frame).
Any APNG file containing sequence errors is treated as an invalid image. The APNG
loader will not attempt to repair and reorder files containing sequence errors.
Saving
~~~~~~
When calling :py:meth:`~PIL.Image.Image.save`, by default only a single frame PNG file
will be saved. To save an APNG file (including a single frame APNG), the ``save_all``
parameter must be set to ``True``. The following parameters can also be set:
**default_image**
Boolean value, specifying whether or not the base image is a default image.
If ``True``, the base image will be used as the default image, and the first image
from the ``append_images`` sequence will be the first APNG animation frame.
If ``False``, the base image will be used as the first APNG animation frame.
Defaults to ``False``.
**append_images**
A list or tuple of images to append as additional frames. Each of the
images in the list can be single or multiframe images. The size of each frame
should match the size of the base image. Also note that if a frame's mode does
not match that of the base image, the frame will be converted to the base image
mode.
**loop**
Integer number of times to loop this APNG, 0 indicates infinite looping.
Defaults to 0.
**duration**
Integer (or list or tuple of integers) length of time to display this APNG frame
(in milliseconds).
Defaults to 0.
**disposal**
An integer (or list or tuple of integers) specifying the APNG disposal
operation to be used for this frame before rendering the next frame.
Defaults to 0.
* 0 (:py:data:`~PIL.PngImagePlugin.APNG_DISPOSE_OP_NONE`, default) -
No disposal is done on this frame before rendering the next frame.
* 1 (:py:data:`PIL.PngImagePlugin.APNG_DISPOSE_OP_BACKGROUND`) -
This frame's modified region is cleared to fully transparent black before
rendering the next frame.
* 2 (:py:data:`~PIL.PngImagePlugin.APNG_DISPOSE_OP_PREVIOUS`) -
This frame's modified region is reverted to the previous frame's contents before
rendering the next frame.
**blend**
An integer (or list or tuple of integers) specifying the APNG blend
operation to be used for this frame before rendering the next frame.
Defaults to 0.
* 0 (:py:data:`~PIL.PngImagePlugin.APNG_BLEND_OP_SOURCE`) -
All color components of this frame, including alpha, overwrite the previous output
image contents.
* 1 (:py:data:`~PIL.PngImagePlugin.APNG_BLEND_OP_OVER`) -
This frame should be alpha composited with the previous output image contents.
.. note::
The ``duration``, ``disposal`` and ``blend`` parameters can be set to lists or tuples to
specify values for each individual frame in the animation. The length of the list or tuple
must be identical to the total number of actual frames in the APNG animation.
If the APNG contains a default image (i.e. ``default_image`` is set to ``True``),
these list or tuple parameters should not include an entry for the default image.
PPM
^^^