imresize and ImageJ

[ijourneaux]

I am trying to understand some differences in the results between ImageJ and
Octave when resizing an image

In imageJ If I start with a gray scale image that is 4000x1200 pixels and
scale it down to 1000x300  then down to 250x75. The default for ImageJ are
bilinear.

If I repeat the same steps in Octave, i.e. imresize(a, .25, linear) the std
deviations are not what I would have expected.
Here are the stdev
                     ImageJ       Octave
4000x1200      4.694          4.694           
1000x300        3.253          4.711
250x75           2.007          4.555

The drop in std dev seen in ImageJ seem to be what I would have expected.
With Octave, the fact that the std dev actaully increased in the first
resize operation seems particularly odd.

Perhaps I am misinterpreting what imresize is supposed to do in Octave?
Appreciate any thoughts.



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