Abstract: A method of configuring an image encoder emulator. Input image data is encoded at an encoding stage comprising a network of inter-connected weights, and decoded at a decoding stage to generate a first distorted version of the input image data. The first distorted version is compared with a second distorted version of the input image data generated using an external encoder to determine a distortion difference score. A rate prediction model is used to predict an encoding bitrate associated with encoding the input image data to a quality corresponding to the first distorted version. A rate difference score is determined by comparing the predicted encoding bitrate with an encoding bitrate used by the external encoder to encode the input image data to a quality corresponding to the second distorted version. The weights of the encoding stage are trained based on the distortion difference score and the rate difference score.