[vtk-developers] ImageThreshold efficiency improvements

[Bill Lorensen]

Folks,
I've made some minor changes to ImageThreshold to improve its performance. On solaris systems I see a two-fold improvement while in Windows I see over 5 times improvement in performance. The culprit was a cast to float for every pixel comparison. This is especially inefficient on Intel machines.

All comparisons are now done using the input data's type. I've run all of the regression tests and they pass.

NOTE: since the comparisons are now done in the native type of the input data, rather than float, some comaprisions may produce different results. These can occur at the boundaries of the threshold intervals.

At any rate, I think the improvement merits the change,

Bill