A computer, including a processor and a memory, the memory including instructions to be executed by the processor to generate a first color image of a road environment, determine one or more value decompositions of one or more of the red, green, and blue channels of the first color image, obtain one or more modified singular value decompositions by modifying respective ones of the singular value decompositions by a non-linear equation and reconstruct a second color image based on the modified one or more singular value decompositions. The instructions can include further instructions to train a deep neural network based on the second color image and operate a vehicle based on the deep neural network.