[Insight-users] problems with median filter

[Carolyn Johnston]

Hello all,

I am using ITK to run some experiments with registration of digital 
elevation models. I have run into a confusing problem using the median 
filter class.

I read in a digital elevation model and convert it to an itk float image 
using a conversion class. I set the image region, the origin, and the 
spacing for the image. I then write the resulting image out in raw format, 
and confirm that it is identical to what I read in.

I then filter the image, and again write the raw output. I have tested the 
gradient magnitude filter, the threshold filter, and the median filter. 
Median filtering seems to introduce a sizeable deterministic shift into the 
output: the other filters I have tried don't do this. The shift is on the 
order of 500 pixels in Y and around 10 or so in X (for a 3600 by 3600 
image). Rows and columns of zeros are introduced as well -- around 15 
columns of zeros and 5 rows of zeros at the boundaries of the original 
image. Other than that, the image wraps at the boundaries.

I suspect there is some parameter I am not setting, or am not setting 
correctly. I stepped through the median filtering code with gdb but did not 
find an uninitialized or default parameter read. What might be causing this 
problem?

thanks,
Carolyn Johnston
Sr. Engineer, Vexcel Corporation