Find directional gradients of 3-D image
imgradientxyz
does not normalize the gradient
output. If the range of the gradient output image has to match the
range of the input image, consider normalizing the gradient image,
depending on the method
argument used. For example,
with a Sobel kernel, the normalization factor is 1/44, for Prewitt,
the normalization factor is 1/18.