This class has been grabbed and modified from ITKv4 source tree. In its original version this class segments all the pixels/voxelswith an intensity between the threshold interval [lower upper] provided by the user. In the modified version, the user is asked to only provide an upper threshold, and all the pixels/voxels with an intensity below it are considered. In order to do so, the BelowThreshold methos is used instead of BetweenThreshold.