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idlanroigroup masking weirdness [message #60140] Mon, 28 April 2008 07:26
Loren Anderson is currently offline  Loren Anderson
Messages: 22
Registered: August 2007
Junior Member
Hi all,
I've been using idlanroigroup to create masks and there I've found
something to be aware of. Let's say you have a background mask that
goes from masked (value = 0, "-") to unmasked (value = 255, "+") like
so:

------++++++
------++++++
------++++++
------++++++
------++++++
------++++++

Now you want to do further masking on this, like so (cut out a
semicircle:

------++++++
-------+++++
--------++++
--------++++
-------++++
------++++++

What you will get will be a *filled* semicircle - it will not be
masked out. This applies only when the boundary goes from 0 to 255
from left to right. This sort of boundary: ++++----- does not produce
this problem. It must have something to do with how the mask array is
filled.

Here's an example: http://people.bu.edu/andersld/mask.jpg

-Loren
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