Hi Stephen,

I don't know much about image analysis, but in the scipy tutorial (7.2 Filtering), there is an example of an image filter that highlights the edges of an image. If I guess correctly, it finds the smoothing spline of the image and then computes the derivative of the spline. A high derivative means that the image intensity shifts rapidly, so maybe that could help you.

David

2006/6/30, stephen emslie <stephenemslie@gmail.com>:
I am in the process of implementing an image processing algorithm that requires following rays extending outwards from a starting point and calculating the intensity derivative at each point. The idea is to find the point where the difference in intensity goes beyond a particular threshold.

Specifically I'm examining an image of an eye to find the pupil, and the edge of the pupil is a sharp change in intensity.

How does one iterate along a line in a 2d matrix, and is there a better way to do this? Is this a problem that linear algebra can help with?

Thanks
Stephen Emslie

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