After an image has been drawn onto a canvas, you may want to
reuse such image further. However, for large images, keeping the
entire image data in memory could cause out of memory errors,
especially on 32-bit machines where it's easier to run out of
Call this method after drawing an image to release any memory
that can be released, normally the decoded image data.
Calling this method may degrade performance since before drawing
an image the image data must be reloaded.
Not all image formats support this method.