Deblocking algorithm for DCT-based compressed images using anisotropic diffusion

Among many image compression approaches, the discrete cosine transform (DCT) is widely used. However, dividing an image into small blocks prior to coding causes "blocking artifacts". A deblocking algorithm is proposed for DCT-based compressed images using anisotropic diffusion; it is derived from the ALM (Alvarez, Lions, Morel) diffusion model (Alvarez, L. et al., SIAM J. Numer. Anal., vol.29, no.3, p.845-66, 1992). It can control the diffusion rate in the normal direction of the edges using a "rate control parameter". It functions not only as an isotropic diffusion at block boundaries of smooth regions, but also as an anisotropic diffusion that diffuses the image only in the normal direction of the edges at edges or block boundaries of texture regions. The rate control parameters at block boundaries are chosen carefully to reduce discontinuities. To avoid oversmoothing of the texture region, a "speed parameter" is employed. The speed parameter makes the diffusion process slow at the texture region, while making it fast at the smooth region.