AN ARITHMETIC CODING SCHEME FOR GRAY-SCALE IMAGES WITH MINIMUM DESCRIPTION LENGTH CRITERION

In the arithmetic coding of the multilevel gray-scale image (128 level s) up to now, the fixed model for the gray-scale image is applied. Thi s paper proposes a method to improve the compression ratio by introduc ing the minimum description length (MDL) into the encoder to describe more precisely the local property of the image and by adaptively selec ting the probabilistic model. In the course of this development, a pra ctical form of MDL criterion is presented to be adaptively applied to the encoding as an approximation to the MDL criterion proposed by Riss anen. A problem in the arithmetic coding of the multilevel gray-scale image using a probabilistic model with a large number of parameters is the deterioration of the compression ratio. To solve this problem, th is paper proposes a convergence acceleration method for the average co de length for the arithmetic encoding of the high-level gray-scale ima ge. Then, based on the proposed acceleration method, the MDL criterion is introduced into the arithmetic coding of the multilevel gray-scale image. Finally, the effectiveness of the proposed coding method is de monstrated by computer simulation.