reader update

I use the vtkImageimport interface to use the same pointer to pass in data for body drawing, the first time the pointer address grayscale range is 0 to 128, color map is 0 to 255, the second time to modify the pointer internal data range to 0 to 255, or the original color map, but this time the body color map is only 0 to 128. This time the reader to perform modified interface can solve this problem,but would like to ask why there is this situation