[matplotlib-devel] image module questions

[John H. <jdh...@ac...>]

I'm starting to think about adding image support and wanted to get
some input about what it should include and how it should be designed.
The ideas are still pretty nascent but here is where I was planning to
start.

Create an image extension built around agg (not backend_agg).  This
would be a free standing extension not tied to any of the backends
with the responsibility of loading image data from a variety of
sources into a pixel buffer, and resizing it to a desired pixel size
(dependent on the axes window) with customizable interpolation.

Inputs: what file formats should be supported?  

  * I can do PNG rather easily since I already had to interface agg
    with png for save capabilities in backend_agg.

  * As for raw pixel data, should we try to support
    grayscale/luminance, rgb and rgba with the platform dependent byte
    ordering problems, or leave it to the user to load these into a
    numeric/numarray and init the image with that?  Should we follow
    PILs lead here and just provide a fromstring method with format
    strings?

  * What raw types should be supported: 8 bit luminance, 16 bit
    luminance, 8 bit rgb, 8bit rgba, 16 bit rgb or rgba?

Resizing: Generally the axes viewport and the image dimensions will
not agree.  Several possible solutions - perhaps all need to be
supported:
 
  * a custom axes creation func that fits the image when you just want
    to view and draw onto single image (ie no multiple subplots).

  * resize to fit, resize constrained aspect ratio, plot in current
    axes and clip image outside axes viewlim

  * with resizing, what pixel interpolation schemes are critical?  agg
    supports several: nearest neighbor, blinear, bicubic, spline,
    sinc.

Backends:

  I am thinking about using the same approach as in ft2font.  Have the
  image backend provide the load/resize/interpolate methods and fill a
  pixel buffer of appropriate size and letting the backends do
  whatever they want with it.  Agg can blend the image with the
  drawing buffer, gtk can draw from an rgba buffer.  Not sure about PS
  yet.  paint and wx can use their respective APIs to copy the pixel
  buffer.


Any other thoughts welcome...

JDH