BUG: add writeable_output=True to pillow plugin to ensure data is writable by default
#976
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Closes: #877, #972
This PR adds the
writeable_outputkwarg to pillow'sreadanditerfunctions. If set to True (default) the plugin will ensure that the returned numpy array is writable, i.e., it will copy the data into a new buffer in cases where pillow would have otherwise returned a read-only array. This has the advantage of allowing in-place modifications of the returned array which makes the plugin backward compatible with v2 and is supposedly less surprising behavior.It does come with a performance penalty though because we may have to copy the pixel data of a (potentially large) image. If, however, read-only is sufficient, e.g., when we copy the decoded data straight into an image batch (aka. image tensor) this extra copy is unnecessary. In such cases, users can set
writeable_output=False. The plugin is then allowed to return read-only arrays if this is faster and users can enjoy improved performance.