[vtkusers] negative values in CT data

[David E. Jones]

There are a lot of vtk users who do volume visualization.  I do
this myself for data collected with microtomography.  There is a
characteristic of the reconstructed data which I don't understand.
It's this:  there are a lot of negative values in the data.  I've
attached a histogram which shows this.  The histogram is symmetric
which suggests that the negative values are meaningful.  I've also
attached a picture of one of the slices with level=.2 and
window=1.4 using the units on the historgram scale.

Is anyone familiar with the occurence of negative values and what
to do with them ?  I know that the negative values need to be
eliminated to use volume rendering.  In the past I've set them
to be 0 but I'm not sure this is correct.

Thanks in advance,
Dave

--
David E Jones
Du Pont Central Research
Experimental Station, Bldg 320
Wilmington, DE 19880-0320


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