Patternbased Assembled DCT Scheme for Image Coding A Patternbased Assembled DCT (PADCT) scheme is proposed as a general framework to fully utilize texture structure property in images in a more feasible and flexible manner. Different patterns can be designed or extracted according to texture structures such as directionality and distribution patterns. Pixels in the block are divided into subpartitions, followed by assembling pixels in each subpartitions together into a compact and efficient form for the succeeding separated one dimensional transform operations, suitable DC prediction and entropy coding schemes are also introduced. PADCT has the advantages of advanced compact energy concentration, efficient usage of memory, fewer categories of one dimensional transform, and adaptability for hardware optimization. Experimental results show that the bitrate reduction over the 2D DCT is up to 35%. It also outperforms significantly than previous typical directional transform schemes in comparison with PSNR or subjective quality.

A New Quality Metric for Compressed Images based on DDCT As the performanceindicator of the image processing algorithms or systems, image quality assessment (IQA) has attracted the attention of many researchers. Aiming to the widely used compression standards, JPEG and JPEG2000, we propose a new no reference (NR) metric for compressed images to do IQA. This metric exploits the causes of distortion by JPEG and JPEG2000, employs the directional discrete cosine transform (DDCT) to obtain the detail and direction information of the images and incorporates with the visual perception to obtain the image quality index. Experimental results show that the proposed metric not only has outstanding performance on JPEG and JPEG2000 images, but also applicable to other types of artifacts.