E1-6 - Sedma Nacionalna Konferencija so Me|unarodno U~estvo...

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ADAPTIVE ARTIFACTS REMOVAL IN BLOCK-BASED- CODED VIDEO SEQUENCES Tomislav Kartalov 1 , Zoran Ivanovski 2 , Ljupco Panovski 3 Faculty of Electrical Engineering – Skopje, Karpos II bb, P.O.B. 574, 1000 Skopje, 1 kartalov@etf.ukim.edu.mk; 2 mars@etf.ukim.edu.mk; 3 panovski@ukim.edu.mk Abstract – A novel post-processing algorithm for suppression of compression artifacts is presented in this paper. The method includes classification of three different types of artifacts (blocking, ringing and DCT-basis artifacts) and appropriate filtering. A two-step classification procedure is used: block-based in the DCT domain and pixel- based in the spatial domain. The filtering is applied adaptively by utilizing the artifact maps obtained in the classification phase. Experimental results show significant reduction of artifacts with no destruction of detail or edges, the overall result being an image with increased visual quality. Keywords – image compression, video compres- sion, compression artifacts, JPEG, MPEG 1. INTRODUCTION Recent research in the field of digital image and video coding has introduced a vast variety of compression and coding techniques and methods for transmitting digital visual information with fewer bits. Unfortunately, no matter how advanced the compression/coding method, a range of distortions is introduced at very low bit rates. An excellent digest of coding distortions in DCT-based video compression standard techniques is given in [1], along with explainations of the origins and of the typical appearances of various artifacts in still images (individual frames), and of temporal distortions in video sequences (H.261, H.263, MPEG1 and MPEG2). Fortunately, the steady progress in microelectronics has led to an enormous increase in computational power of coding and decoding devices, thus making it possible to upgrade standard coding/decoding procedures with steps enabling them to keep abreast of the persistent demand for lower bit rate applications without sacrificing their time performance. The easiest way to suppress the coding artifacts is to intervene after the coding/decoding process with some post-processing algorithm, which would artificially improve the image quality. A very solid summary of the post-processing techniques for coding distortions removal is presented in [2]. Many authors [1]-[7] agree that local image characteristics are very important for the visibility of the distortions. For example, blocking and ringing artifacts [1] are much less visible in image regions with high spatial activity than in plain areas, so they only need to be filtered out in the plain areas. Similarly, it is better not to filter areas rich in details in order to preserve the sharpness of edges and textures. Consequently, this brings out the necessity of making some sort of pixel classification that would be used as a guide for adaptive application of filtering. Several iterative post-processing techniques, based on local image characteristics, for filtering out blocking and ringing
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E1-6 - Sedma Nacionalna Konferencija so Me|unarodno U~estvo...

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