About brightness

[EDIT: 20110523 17:15 CDT - reformat. clarify - WDR]

Hello everyone, I have a trouble with the brightness in a pic that I take:

http://i55.tinypic.com/2s1kt2g.jpg

I'm new in Matlab anyone can help me please? I need to remove the brightness in the edges, then to binarize just to see the white points, the picture is of bacterial colonies. Thanks!

PS: sorry for my bad English.

Answer 1

[Walter Roberson]

I suggest im2bw perhaps in combination with graythresh

[Andre Asfar]

Thanks!, I will try