[Insight-users] threshold levels for pixels in itkThresholdImageFilter

[danieljohnsonusa at netscape.net]

I am using  itkThresholdImageFilter to threshold a dicom image.  I am 
using the ThresholdOutside method to specify the range of pixel to 
leave unfiltered.  I initially set my upper and lower thresholds to 
values between 0 and 255, but I kept getting that everything was above 
the threshold.  I did some experimenting and  found the range of 
intensities that filtered what I wanted ended up being 6000 to 300000.  
Can anyone explain the intesity mapping range of values for a dicom 
image in itk?  Is this intensity number RGB pixel values all multiplied 
together, and if so, is there a way to specify thresholds individually 
to each instead of all 3 multiplied together?  Is there a way to tell 
how the pixels are formatted in your input image and convert between 
formats like RGB to greyscale?  A reference to any type of 
documentation that explains pixel intensities in the different formats 
would be greatly appreciated.

Thanks,

Daniel