A quantization level is determined for use by an encoder in encoding an image in accordance with a target number of bits. For each section of the image, the pixels are analyzed to estimate the complexity of the image section. For each of a plurality of candidate quantization levels, a relationship and the estimated complexity of the image sections are used to estimate the number of bits that would be generated by encoding the image with the encoder using the respective candidate quantization level, and based thereon one of the candidate quantization levels is selected. The relationship is a function of the quantization level used by the encoder, and is for use in relating the complexity of an image section to the number of bits that would be generated by encoding that image section with the encoder. The encoder uses the selected quantization level in encoding the image.