[Numpy-discussion] numarray, nd_image transforms, and multi-channel images

Alexandre Guimond alexandre.guimond at mirada-solutions.com
Wed Apr 13 18:10:47 CDT 2005


Hi all.
 
I've been looking at numarray to do some image processing. A lot of the
work I do deal with transforming images, either with affine
transformations, or vector field. Numarray seems somewhat well equiped
to address these issues, but I am concerned about one aspect. It seems
that the transformation code (affine_transforrm and geometric_transform)
computes input coordonates for every output coordinate in the resulting
array. If I have an RGB image for which the transformation is the same
for all 3 RGB channels, I would assume that this will triple the
workload unncessarily. It might have a dramatic effect for the geometric
transformation which will most often be slower then affine. Is there any
way around this, e.g. is it possible to specify numarray to use the same
interpolation coefficients for the last "n" dimention of the array, or
to tell numarray to only compute interpolation coefficients and apply
those seperatly for each channel?
 
thx for any help / info.
 
alex.
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