1. A method of processing encoded image data representing at least a portion of an image, the method comprising the steps of: accessing a set of encoded image data stored in a memory; operating a processor to perform a JPEG decoding operation on the accessed set of encoded image data, said JPEG decoding operation including performing MQ decoding by processing: i) a base value D, ii) a subinterval length Q which is a sub-portion of the total coding interval length A; iii) a discounted total interval value Ad, said discounted total interval value being equal to a full coding interval A, plus said subinterval length Q, minus said base value D; iv) a discounted code value, Cd, said discounted code value being equal to a code value, C, plus said subinterval length Q, minus said base value D; and v) a predicted symbol bit value S; said processing including: i) computing a first value Amqmq which is equal to (Ad+D−Q); ii) computing a second value Cmq which is equal to Cd +D; and iii) performing a logical shift right operation by the number of bit positions (N−1) on the value (Cmq XOR Amqmq) where N is the number of bit positions used to represent each of Cmq and Amqmq, to generate a symbol indicator value indicating whether the received predicated symbol bit value S is incorrect, said generated symbol indicator value indicating that said received predicted symbol bit value is incorrect when said generated symbol indicator value assumes the value one; generating a set of decoded image data, from a result of the processing performed as part of said MQ decoding, said result including said generated symbol indicator value; and supplying decoded image data from said generated set of decoded image data to a display device.