Bit Allocation with Visual Attention and Visual Distortion Sensitivity

In this work, a novel bit allocation method based on visual attention and distortion sensitivity is developed for JPEG2000. Although, visual attention map for an image can be measured by using well-known saliency map methods, true visual attention map can be obtained by conducting experiments to determine fixation points and their durations. A perception model might turn these duration of fixations into visual attention levels. Besides visual attention, visual distortion sensitivity may guide the bit allocation process effectively. This is because human visual system is more sensitive to the distortion around the edges than the distortion in the complex textured areas. In this work, a novel visual distortion sensitivity method that considers all edges without using a threshold for gradient magnitude and uses local entropy of gradient orientation distribution is proposed. Thus, the visual attention and the distortion sensitivity level of each code-block determine its quantization parameters. Using bit allocation based on the visual attention map provides higher subjective evaluation score than using bit allocation based on the post compression rate-distortion optimization method or on a previously proposed method based on the saliency map. Secondly, it is shown that the use of visual distortion sensitivity allows higher objective evaluation scores to be attained.