1. A method of generating a downsampled image from a first image, comprising: at a processor, receiving a first image, the first image comprising a plurality of regions, each region comprising a plurality of pixels; at the processor, combining pixel values of pixels within a plurality of adjacent regions of the first image to generate downsampled pixel values; in a storage device, storing the downsampled pixel values; and at the processor, generating a downsampled image using the downsampled pixel values as a region of the downsampled image; wherein combining pixel values from pixels within a plurality of adjacent regions of the first image comprises: at the processor, identifying a pixel within each of the adjacent regions, each identified pixel having a common relative location with respect to its region; and at the processor, aggregating the identified pixels to generate a pixel value for the downsampled image.