perimeter of a blob

[Ben Tupper <tupper(at)seadas.bigelow.org>]

I am looking for an efficient means of finding the perimeter of contiguous
blobs of pixels within an image.   These blobs are the regions
returned by the LABEL_REGION function.  I have been using the trusty
brute-force-and-ignorance appraoch where I scan rows and columns within
each blob,  recording the min and max coordinates of each row/column.  
It is a cumbersome task and leaves gaps in certain areas (especially concavities
in the blob.)

I'ld like to try something that does the following:

    Input  image and blob info  -> Something mysterious happens inside the computer -> Output the index values of the perimeter of the blob

I think this closely approximates the reverse of POLYFILLV (pretty close anyhow.)

Any suggestions?

Thanks in advance,

Ben

-- 
Ben Tupper

Bigelow Laboratory for Ocean Science
tupper@seadas.bigelow.org

pemaquidriver@tidewater.net