I. INTRODUCTIONA. INTRA FRAMESII. Total number of bits usedIEEE SIGNAL PROCESSING LETTERS, VOL. XX, NO. XX, XXXX 200XAbstract— Blocking artifacts are visible in the decodedframes of most video coding standards at low bit ratecoding. Latest video coding standard H.264/AVC uses anin-loop deblocking filter to remove the blocking artifacts.The main drawback of this filter is its highimplementation complexity. In this paper, we propose anin-loop deblocking filter to remove the blocking artifacts.In the proposed method, the maximum and minimumvalues among the six pixels across an edge are computed todecide whether the pixels of the block should be filtered ornot. For intra frames, again the block is classified assmooth or mildly textured region. Depending on theclassification of the block, the appropriate filter is appliedto that block. The main advantage of the proposed methodis its low complexity compared to JM 9.8 (H.264Software). A performance comparison of the proposedmethod and the current method is presented.Index Terms— Deblocking filter, Post filter, Loop filter,H.264 standard. EDICS Category: IMD-CODEI. INTRODUCTIONSignal source compression methods and coding bit ratesnormally influence the perceptual quality of compressedimages and video [1]. In general, the less the bit rates thesevere the coding artifacts manifest in the reconstructedvideo. Lower bit rates are desirable in many applications likevideo streaming because of the channel bandwidthconstraints. The block discrete cosine transform (BDCT)based coding scheme introduces blocking artifacts in flatregions and ringing artifacts along object edges at low bitrates [1]. Deblocking filters are used to remove the blockingartifacts in the decoded video. Although the deblocking filtersimprove the objective and subjective qualities of output videoframes, they are usually computationally intensive. There are number of deblocking algorithms proposed forreducing the block artifacts in BDCT based compressedimages with minimal smoothing of true edges. They can beclassified into three key categories: Projection onto convexsets (POCS), weighted sum of pixels across block boundaries,and adaptive filters. POCS based algorithm [2] iterativelyprojects back and forth between two sets on the entire picture.Its relative computation and implementation complexity isManuscript received July xx, 2006; revised Xxxxx xx, 20xxHitesh Yadav and Dr. K. R. Rao are with the Electrical EngineeringDepartment, University of Texas at Arlington, TX 76010 USA (e-mail:[email protected], [email protected])high compared to other two algorithms. It gives best qualityvisually with most of the video compared to other twomethods. The weighted sum based algorithms [3]computation complexity is high compared to the adaptivealgorithms. As adaptive algorithms [4] computationalcomplexity is low they are preferred algorithms for real timeimplementation. H.264/AVC uses an adaptive in-loopdeblocking filter to remove the blocking artifacts visible indecoded frames at low bit rate coding. The main drawback of this deblocking filter is itsimplementation complexity. Analysis of run time profiles ofdecoder sub-functions indicates that the deblocking filterprocess in H.264 is the most computationally intensive part[5]. Though recently efficient techniques to reduce theimplementation complexity have been proposed [6]-[8], thecomplexity still cannot be reduced significantly because of theflow of algorithm itself. The program code [9] includesextensive conditional branching. This makes codes unsuitablefor deeply pipelined processor and ASIC implementation. Inaddition, this program code exposes little parallelism. Hencethis code is unsuitable for VLIW processors, which areotherwise well suited to video encoding/decodingapplications.As we can see from the above, H.264/AVC has highimplementation complexity. In this paper, we present asimpler algorithm for the deblocking filter which reduces theimplementation complexity while maintaining the perceptualquality of the existing deblocking algorithm. In section 2, wepresent the algorithm for both inter and intra frames. Insection 3, the results obtained from the proposed algorithmand the one obtained from the JM reference software [9] arediscussed. II. PROPOSED ALGORITHMThe blocking artifacts are visible in both intra and interframes. The basic operation of the deblocking filter is asfollows: The deblocking filter is applied to all the edges of4x4 pixels blocks in each macroblock except to the edges onthe boundary of a frame or a slice. For each block, verticaledges are filtered from left to right first, and then horizontaledges are filtered from top to bottom. The decoded process isrepeated for all macroblocks in a frame. The one-dimensionalview of a 4x4 block edge is shown in Fig. 1. Here q0, q1, q2,q3 represent the values loaded from the current 4x4 block andthe p0, p1, p2, p3 represent the 4x4 block adjacent to thecurrent 4x4 block.A. INTRA FRAMESIntra frames are more susceptible to blocking artifactscompared to inter frames [10]. The smooth blocks in an intraframe have more severe blocking artifacts compared to otherOptimization of the Deblocking filter in H.264codec for real time implementationHitesh Yadav, Student Member IEEE and K. R. Rao, Member, IEEE1IEEE SIGNAL PROCESSING LETTERS, VOL. XX, NO. XX, XXXX 200Xblocks [10]. The proposed method as applied to intra framesis shown in Fig. 2.The first three blocks in Fig. 2. check for the conditions atthe slice boundaries. The user sets these conditions. Thesethree blocks are the same as used by the existing deblockingfilter in H.264. The next step in Fig. 2 is to compute themaximum and minimum values among the six pixels acrossan edge (p2, p1, p0, q0, q1, q2) and then calculate the differencebetween the maximum and the minimum value. If thisdifference is greater
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