Combined Frequency and Spatial Domain Algorithm for the Removal of Blocking Artifacts
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Combined Frequency and Spatial Domain Algorithm for the Removal of Blocking Artifacts George A. Triantafyllidis Information Processing Laboratory, Electrical and Computer Engineering Department, Aristotle University of Thessaloniki, Thessaloniki 54006, Greece Email: [email protected]
Dimitrios Tzovaras Informatics and Telematics Institute, 1st Km Thermi-Panorama Road, Thermi-Thessaloniki 57001, Greece Email: [email protected]
Demetrios Sampson Informatics and Telematics Institute, 1st Km Thermi-Panorama Road, Thermi-Thessaloniki 57001, Greece Email: [email protected]
Michael G. Strintzis Information Processing Laboratory, Electrical and Computer Engineering Department, Aristotle University of Thessaloniki, Thessaloniki 54006, Greece Informatics and Telematics Institute, 1st Km Thermi-Panorama Road, Thermi-Thessaloniki 57001, Greece Email: [email protected] Received 31 July 2001 and in revised form 7 February 2002 A novel combined frequency and spatial domain method is presented in this paper for blockiness reduction for low bit rate compressed images. The method consists of two stages: in the first, better estimates of the reconstructed DCT coefficients are obtained based on their observed probability distribution. In the second, an efficient postprocessing scheme consisting of a region classification algorithm and a spatial adaptive filtering is applied for blockiness removal. The type of filtering is decided on the basis of an estimation of the local characteristics of the coded image. The main advantage of the proposed method is the efficient combination and design of these two stages which are acting complementarily for the reduction of blocking artifacts. This approach is shown to produce excellent results in removing blocking artifacts. The efficient performance of the proposed algorithm is due, firstly, to the proposition that the shape and the position of the filter kernel are adjusted according to the characteristics of the local image region and secondly, to the employment of the modified improved DCT coefficients by the postprocessing filter. Experimental results illustrating the performance of the proposed method are presented and evaluated. Keywords and phrases: blocking artifacts, DCT coefficient restoration, spatial adaptive filtering.
1.
INTRODUCTION
The block based discrete cosine transform (B-DCT) scheme is a fundamental component of many image and video compression standards. Due to its performance on highly correlated signals which is close to that of the (optimal) KarhunenLoeve transform (KLT), and the availability of fast software and hardware implementations, the B-DCT is highly popular in application to image compression. In particular, the BDCT is used in most of current image and video compression standards, such as JPEG [1, 2] and MPEG [3]. A major problem related to the DCT techniques is that
the decoded images, especially at low bit rates, exhibit visually annoying gray-level discontinuities along the block boundaries, commonly referred to as blocking artifacts. This is due to the fact th
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