Hi all, I' m developing a medical software named InVesalius [1], it is a free software. It uses numpy arrays to store the medical images (CT and MRI) and the mask, the mask is used to mark the region of interest and to create 3D surfaces. Those array generally have 512x512 elements. The mask is created based in threshold, with lower and upper bound, this way: mask = numpy.zeros(medical_image.shape, dtype="uint16") mask[ numpy.logical_and( medical_image >= lower, medical_image <= upper)] = 255 Where lower and upper are the threshold bounds. Here I' m marking the array positions where medical_image is between the threshold bounds with 255, where isn' t with 0. The question is: Is there a better way to do that? Thank! [1] - svn.softwarepublico.gov.br/trac/invesalius