[Qgis-developer] Contrast Stretch Based on Current View

[Jeff Ruby]

I'm new to QGIS development.  I want to do a min-max contrast stretch
on raster layer based on the portion of the image currently displayed
in the window.  I believe I can figure out how to write a plugin that
will set the min max values, my problem is obtaining the min and max
values for the portion of the raster band the is currently displayed.
Any advice on how to do this?