Adaptive decision on the priority of horizontal or vertical direction for the SA-DCT

SA-DCT has shown excellent results for image compression at medium and high bit rates. Moreover, the decision on the direction of the first ID-processing of the SA-DCT influences the overall coding performance. Some methods for selecting this preferential direction are based on shape information only and the isolated use of any of them is not always able to outperform the other ones. A more efficient scheme, which is based on a trade-off between quality and rate has been proposed, but it is computationally too heavy. This paper introduces a novel scheme that uses a morphological feature to adaptively choose the best strategy (among three different ones) to determine the preferential direction for the SA-DCT. It provides comparable or better performance than those schemes which use shape information only, with lower computational load than the one which is based on quality versus rate.