1. A system, comprising: a processor configured to: receive a first image; assign an initial label to at least some pixels in the first image, including by assigning a first label to a first pixel; determine, based at least in part on labels of spectral neighbors of the first pixel, that the first pixel's label should be replaced with a different label; update the first pixel's label with the different label; receive a second image; and generate as output a composite classification image wherein a label of a given pixel in the composite classification image is selected from one of a label determined for the given pixel as it appears in the first image and a label for the given pixel as it appears in the second image; and a memory coupled to the processor and configured to provide the processor with instructions.