[Numpy-discussion] Update for IM. a small image processing system

RJS rays at san.rr.com
Wed Jan 7 22:35:04 CST 2004

Hello Peter,

 > On Wednesday 07 January 2004 07:50, RJS wrote:

 > >   Most programs I have seen align a selected sub-image, then shift
 > >  the whole image/array (without rotation, although that would be 
 > If I understand you well, you essentially want to estimate a shift 
between two
 > images. I have some code that can do that. I do not intend to include 
that in
 > nd_image for now, but I can send you the code.

Yes, please. I sure that it's better/faster than my PIL or PythonMagick 
efforts. I don't know about machine vision etc, but shift is indispensable 
for video astronomy.

 > >  2. A fast method(ology) to do weighted sums of 2D arrays with a mask
 > >  available for each array.
 > I think this can be achieved relatively easily with standard numarray
 > operations.

Yes, it is straight-forward, in a way, but I'm always scouring the net for 
C and Python algorithms. Very (most?) often they're better than my own. 
This app is really a proof-of-concept; hopefully others will incorporate 
the "clipped image stacking" into their already fine astro apps.
The problem is that the standard methods - median, mean, or summing - all 
suffer when long images in unequal exposure stacks have large clipped regions.



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