Slice 3D image to obtain multiple 2D images

i have 3D images in .nii format and i want to slice them to obtain multiple 2D images Each 3D image are of size 256*256*150 and I want to obtain slices from a midpoint of z-axis like [:,:,75] to [:,:,100] interleaving 5 slices . For example [:,:,75],[:,:,80], [:,:,85]. Tricky part is i have to crop the image as well to leave the black boundary part and maintain contrast stretching of the image.