Resampling vs Registration

Both resampling and registration (also spatial normalization/warping) modify the underlying matrices of one image to match that of another. But unlike resampling, only registration and warping inspect and modify based on the data within the images.

From Andy's Brain Book

Resampling means changing either the resolution, dimensions, or both the resolution and dimensions of an image.

Compared that to warping where

each brain [within an image] needs to be transformed

3dresample is an AFNI tool to resample an inset to the “master”. We can compare it to FSL's flirt which reorients a brain to a reference (-ref). Both commands produce a new image with the same grid. However, the output of the flirt command will have a brain that's been moved. The value of the voxel at (i,j) (1,1) will be different in the input, resampled (3dresample), and registered (flirt) images.