An image block comprising multiple image elements is compressed into at least one base codeword, interval codeword and index sequence. The respective bit-length of at least two of the codewords and the index sequence are dynamically defined based on the original vector components of the image elements, though the total bit length of the resulting compressed block is constant. The base codeword represents a base value and the interval codeword represents an interval. This interval encompasses multiple component values relative the base value. The index sequence is indicative of, for each image element, a component value selected from the multiple available values.