Image stats - going from Matlab to Python

Fernando Perez fperez.net at gmail.com
Mon Jan 31 08:22:19 CET 2005


tjv at hotmail.com wrote:

> Hi all,
> I am working with images in python using PIL. I come from a MATLAB
> background so I am finding it to be sometimes frustrating to do things
> correctly and quickly. All I need to do is load an image and store a
> list of pixel coordinates at which the alpha channel is set to 1.
> In Matlab this would be easy...Lets say we have a 2x2x4 array that
> represents the image. I would just type something like:
> 
> indices = find(im(:,:,3)==1);
> 
> then work with indices to get xy coords. Is there a similar way to
> accomplish the same thing in python and PIL without having a nested for
> loop and checking every pixel?
> I would appreciate advice. Thanks very much for your attention!

The kind of array functionality which you have in mind is implemented in python
by the Numeric/Numarray libraries.  You can (and should) use the PIL for the
more image-specific tasks, but basic array things are done via those others. 
You may also want to look at matplotlib, for a high level, matlab-compatible
plotting library.

Regards,

f




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