1. A method of performing MQ-decoder processing on encoded image data representing at least a portion of an image, the method comprising the steps of: operating a processor implemented in hardware to: receive as input: 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; compute: a first value Amqmq which is equal to (Ad+D−Q); a second value Cmq which is equal to Cd+D; and perform 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 indicating that said received predicted symbol bit value is incorrect when said symbol indicator value assumes the value one.