An image processing system includes an input interface to receive a set of pairs of images to train an image generator, each pair includes a low-resolution image of a scene and a high-resolution image of the scene, a processor to train the image generator by solving an optimization problem to produce parameters of the image generator reducing distances between image gradients of the high-resolution images and the corresponding low-resolution images upsampled by the image generator, and an output interface to render the parameters of the image generator.