1. A method comprising: determining a first intermediate computation based on even pixels of an image vector associated with a first image, wherein the first intermediate computation includes calculating a box filter value for an even pixel; determining a second intermediate computation separate from the first intermediate computation and based on odd pixels of the image vector, wherein the second intermediate computation includes calculating a box filter value for an odd pixel; combining the first intermediate computation and the second intermediate computation into a Hessian matrix computation; and matching the first image to a second image based at least in part on the Hessian matrix computation.