The quality (e.g., resolution) of image data, video data, and sound data representing a scene or signal is enhanced by a quality enhancement function trained on high quality and low quality representations of a portion of the same scene or signal. The enhancement function is thus optimized to the most relevant input. A training algorithm uses low quality image of a scene or scene portion, along with a high quality image of the same scene or scene portion, to optimize the parameters of a quality enhancement function. The optimized enhancement function is then used to enhance other low quality images of the scene or scene portion. Sound data is enhanced by using a low resolution sample of a portion of a signal, and a high resolution sample of the same signal portion, to train a quality enhancement function which is then used to enhance the remainder of the signal.