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Proceedings Paper

A perceptual optimization of H.264/AVC bit allocation at the frame and macroblock levels
Author(s): M. Hrarti; H. Saadane; M.-C. Larabi; A. Tamtaoui; D. Aboutajdine
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Paper Abstract

In H.264/AVC rate control algorithm, the bit allocation process and the QP determination are not optimal. At frame layer, there is an implicit assumption considering that the video sequence is more or less stationary and consequently the neighbouring frames have similar characteristics. So, the target Bit-Rate for each frame is estimated using a straightforward process that allocates an equal bit budget for each frame regardless of its temporal and spatial complexities. This uniform allocation is surely not suited especially for all types of video sequences. The target bits determination at macroblock layer uses the MAD (Mean Absolute Difference) ratio as a complexity measure in order to promote interesting macroblocks, but this measure remains inefficient in handling macroblock characteristics. In a previous work we have proposed Rate-Quantization (R-Q) models for Intra and Inter frames used to deal with the QP determination shortcoming. In this paper, we look to overcome the limitation of the bit allocation process at the frame and the macroblock layers. At the frame level, we enhance the bit allocation process by exploiting frame complexity measures. Thereby, the target bit determination for P-frames is adjusted by combining two temporal measures: The first one is a motion ratio determined from actual bits used to encode previous frames. The second measure exploits both the difference between two consecutive frames and the histogram of this difference. At macroblock level, the visual saliency is used in the bit allocation process. The basic idea is to promote salient macroblocks. Hence, a saliency map, based on a Bottom-Up approach, is generated and a macroblock classification is performed. This classification is then used to accurately adjust UBitsH264 which represents the usual bit budget estimated by H.264/AVC bit allocation process. For salient macroblocks the adjustment leads to a bit budget which is always larger than UBitsH264. The extra bits added to code these macroblocks are deducted from the bit budget allocated to the non-salient macroblocks. Simulations have been carried out using JM15.0 reference software, several video sequences and different target Bit-Rates. In comparison with JM15.0 algorithm, the proposed approach improves the coding efficiency in terms of PSNR/PSNR-HVS (up to +2dB/+3dB). Furthermore, the bandwidth constraint is always satisfied because the actual Bit-Rate is always lower than or equal to the target Bit-Rate.

Paper Details

Date Published: 24 January 2012
PDF: 11 pages
Proc. SPIE 8293, Image Quality and System Performance IX, 82930V (24 January 2012);
Show Author Affiliations
M. Hrarti, XLim-SIC Lab., Univ of Poitiers (France)
GSCM-LRIT Lab., CNRS, Univ. MohamedV (Morocco)
H. Saadane, XLim-SIC Lab., Univ of Poitiers (France)
Nantes Univ. (France)
M.-C. Larabi, XLim-SIC Lab., Univ of Poitiers (France)
A. Tamtaoui, National Institute of Post and Telecommunications (Morocco)
D. Aboutajdine, GSCM-LRIT Lab., CNRS, Univ. MohamedV (Morocco)

Published in SPIE Proceedings Vol. 8293:
Image Quality and System Performance IX
Frans Gaykema; Peter D. Burns, Editor(s)

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