A signal processing system for allocating data rates for encoding a plurality of signals to obtain a multiplexed bundle of signals, the signal processing system being configured to: receive a plurality of input signals, a given input signal of the plurality of input signals comprising a sequence of images; generate residual data and obtain complexity information on an image-by-image basis, comprising, for a respective image of the sequence of images: generating residual data based (a) on the respective image, the respective image having a first level of quality, and (b) on a rendition of the respective image at a second, lower level of quality, the signal processing system being configured to generate the residual data by: processing the respective image having the first level of quality to generate the rendition of the respective image at the second, lower level of quality; processing the generated rendition of the respective image at the second, lower level of quality to generate a rendition of the respective image at the first level of quality; and generating the residual data based on the difference between the respective image at the first level of quality and the generated rendition of the respective image at the first level of quality; and before encoding the respective image, obtaining complexity information relating to the respective image based at least in part on the generated residual data for the respective image; derive a data rate target for each of the plurality of input signals in dependence on an overall data rate target for the plurality of input signals, the data rate target for the given input signal depending at least in part on the complexity information; encode the plurality of input signals in accordance with the respective derived data rate targets to obtain a plurality of encoded signals; multiplex the plurality of encoded signals to obtain a multiplexed bundle of encoded signals, the multiplexed bundle of encoded signals having a combined data rate satisfying the overall data rate target; and output the multiplexed bundle of encoded signals. receive a plurality of input signals, a given input signal of the plurality of input signals comprising a sequence of images; generate residual data and obtain complexity information on an image-by-image basis, comprising, for a respective image of the sequence of images: generating residual data based (a) on the respective image, the respective image having a first level of quality, and (b) on a rendition of the respective image at a second, lower level of quality, the signal processing system being configured to generate the residual data by: processing the respective image having the first level of quality to generate the rendition of the respective image at the second, lower level of quality; processing the generated rendition of the respective image at the second, lower level of quality to generate a rendition of the respective image at the first level of quality; and generating the residual data based on the difference between the respective image at the first level of quality and the generated rendition of the respective image at the first level of quality; and before encoding the respective image, obtaining complexity information relating to the respective image based at least in part on the generated residual data for the respective image; generating residual data based (a) on the respective image, the respective image having a first level of quality, and (b) on a rendition of the respective image at a second, lower level of quality, the signal processing system being configured to generate the residual data by: processing the respective image having the first level of quality to generate the rendition of the respective image at the second, lower level of quality; processing the generated rendition of the respective image at the second, lower level of quality to generate a rendition of the respective image at the first level of quality; and generating the residual data based on the difference between the respective image at the first level of quality and the generated rendition of the respective image at the first level of quality; and processing the respective image having the first level of quality to generate the rendition of the respective image at the second, lower level of quality; processing the generated rendition of the respective image at the second, lower level of quality to generate a rendition of the respective image at the first level of quality; and generating the residual data based on the difference between the respective image at the first level of quality and the generated rendition of the respective image at the first level of quality; and before encoding the respective image, obtaining complexity information relating to the respective image based at least in part on the generated residual data for the respective image; derive a data rate target for each of the plurality of input signals in dependence on an overall data rate target for the plurality of input signals, the data rate target for the given input signal depending at least in part on the complexity information; encode the plurality of input signals in accordance with the respective derived data rate targets to obtain a plurality of encoded signals; multiplex the plurality of encoded signals to obtain a multiplexed bundle of encoded signals, the multiplexed bundle of encoded signals having a combined data rate satisfying the overall data rate target; and output the multiplexed bundle of encoded signals.