When encoding an array of data elements using an encoding process that generates an array of quantized frequency domain coefficients corresponding to an array of difference values between a source block of data elements of the array of data elements being encoded and a reference block of data elements, a bit count value for encoding an array of quantized frequency domain coefficients to be used to select whether to encode the source block in accordance with a particular set of encoding options is estimated by estimating a bit count value for encoding the locations of the non-zero quantized frequency domain coefficients in the array of quantized frequency domain coefficients based on the number of non-zero frequency domain coefficients in the array of quantized frequency domain coefficients.