Update concepts.rst; clarify 'bands'

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Charles Merriam 2015-09-03 13:26:04 -07:00
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@ -4,12 +4,17 @@ Concepts
The Python Imaging Library handles *raster images*; that is, rectangles of
pixel data.
.. _concept-bands:
Bands
-----
An image can consist of one or more bands of data. The Python Imaging Library
allows you to store several bands in a single image, provided they all have the
same dimensions and depth.
same dimensions and depth. For example, a PNG image might have 'R', 'G', 'B',
and 'A' bands for the red, green, blue, and alpha transparency values. Many
operations act on each band separately, e.g., histograms. It is often useful to
think of each pixel as having one value per band.
To get the number and names of bands in an image, use the
:py:meth:`~PIL.Image.Image.getbands` method.