Wonkyun Kim

16x16 macroblock partition size prediction for H.264 P slices

H.264 uses variable block sizes for macroblock partition. The H.264 encoder allows 2 intra coding modes and 5 inter coding modes for a macroblock in a P slice. This is the most essential part for high compression efficiency but requires many computations to decide the most suitable coding mode. In this paper, we present a fast mode decision algorithm for H.264 P slices. To reduce complexity, we analyze the results of P16times16 ME (motion estimation) of a macroblock according to the proposed decision model, and if this macroblock is considered to be coded with a larger mode, we prevent motion estimations for smaller modes. From statistical analysis, we define a decision model which estimates whether the macroblock partition size is further divided or not. Our experimental results show that the proposed algorithm can achieve 11-63% computational savings without significant degradation of visual quality and increase in bit rate

Complexity control strategy for real-time H.264/AVC encoder

The H.264/AVC encoder acquires high coding efficiency by using the various coding techniques, but requires very high computational complexity. Therefore, H.264/AVC encoder causes the problem of preserving acceptable video coding performance in the low-power/processor environments, such as wireless mobile. To optimize the rate-distortion (R-D) and complexity, we analyze the encoding structure and establish an analytic model for complexity. From this analysis, we propose a new approach for real-time encoder which maintains both frame rate and video quality. An encoding time control algorithm investigates the results of P16×16 motion estimation (ME) in the current frame and decides the number of skipped macro-blocks (MBs) in order to encode the frame within the allocated target encoding time. A complexity control algorithm manages the coding complexity of each frame by preventing motion estimations for smaller modes. Simulation results show that compared to the existing algorithm, the proposed algorithm can maintain frame rate without significant degradation of visual quality and increase in bit rate.

Contrast enhancement using histogram equalization based on logarithmic mapping

A widely used contrast enhancement method, the histogram equalization (HE) often produces images with unnatural appearances and visually disturbing artifacts because the HE compels the enhanced image to follow the uniform distribution. An adaptive histogram equalization using logarithmic mapping is presented, with a proposed algorithm based on a bin underflow and overflow method that achieves contrast enhancement by putting constraints on each histogram component differently. To incorporate characteristics of the human visual system, the logarithmic mapping function is used as constraint function, while the rate of contrast enhancement is controlled by determining the control parameters with the characteristics of the original image. The experimental results show that the proposed algorithm not only keeps the original histogram shape features, but also enhances the contrast effectively. Due to its simplicity, the proposed algorithm can be applied by simple hardware and processed in a real-time system.

Fast Mode Decision Algorithm Using Efficient Block Skip Techniques for H.264 P Slices

In this paper, we propose a fast algorithm that can reduce the complexity for inter mode decision of the H.264 encoder by minimizing a large number of calculations of inter mode decision process adaptively. The main idea is to use the technique skipping unnecessary macroblock modes. We focus on two block size modes, which is 16x16 and 8x8 block size modes, in proposed algorithm. The percentage of 16x16 block size modes is the largest in most of the sequences. This means that many redundant mode calculations can be removed. The percentage of 8x8 block size mode is small. But time consumption caused in the mode decision of encoder is very considerable. Therefore if we can extract the unnecessary 8x8 block size mode calculation well, a large amount of time can be saved in total encoding process. The experimental results show that the proposed algorithm can achieve up to 43% speed up ratio with a little PSNR loss. Increase of total bits encoded is also not much noticeable.

Remote sensing image enhancement based on singular value decomposition

A satellite image enhancement method based on singular value decomposition (SVD) is presented. The proposed method consists mainly of four steps: image decomposition, adjustable contrast enhancement, noise reduction, and image composition. The method decomposes an image into its singular values, from which the luminance information can be obtained using SVD. In turn, adjustable contrast enhancement is applied by changing the singular values, which are controlled by characteristic-based contrast-level parameters. In the noise reduction process, the high-frequency elements, such as noise, are removed using rank approximation. In the final image composition process, the proposed algorithm combines color and luminance components in order to preserve color consistency. Experimental results show that the proposed scheme has less noise than the conventional methods and improves contrast performance while preserving details.

Edge Direction-Based Simple Resampling Algorithm

We considered the problem of resampling video frames to adjust from 176x72 to 352times288 display formats. Images were divided into six regions according to six different edge directions and different reconstruction techniques were employed in each region. The algorithms developed and implemented on this system include edge pattern-based region classifier and resampling strategies for digital display. The performance of the proposed algorithm is compared to conventional methods such as nearest-neighbor interpolation, bilinear interpolation, and simple cubic curve fitting interpolation.

Fast intra mode decision algorithm using sub-sampled pixels

Intra prediction is a significant technique in H.264/AVC reference software. However, it has heavy computational complexity. In order to solve this problem, many fast algorithms have been proposed. In this paper, we propose a fast intra mode decision algorithm which predicts the edge direction of the current block using sub-sampled pixels to reduce high computational complexity of the H.264/AVC encoder. The proposed algorithm shows that it not only improves the coding performance but also reduces the computational complexity of the H.264/AVC encoder. The experimental results show that the proposed algorithm achieves the encoding time reduction of 75.74% on an average with slight peak signal-to-noise ratio (PSNR) drop and bit-rate increment.

Sub-Sampled Pixels based Fast Mode Selection Algorithm for Intra Prediction in H.264/AVC

Intra prediction is one of the significant techniques in H.264/AVC reference software; however, it has heavy computational complexity. In order to solve this problem, many fast algorithms have been proposed. In this paper, we propose a fast intra mode decision algorithm which predicts the edge direction of the current block using sub-sampled pixels to reduce high computational complexity of the H.264/AVC encoder. The proposed algorithm shows that it not only improves the coding performance but also reduces the computational complexity of the H.264/AVC encoder compared to previous algorithms. The experimental results show that the proposed algorithm achieves the encoding time reduction of 75.93% on an average with slight peak signal-to-noise ratio (PSNR) drop and bit-rate increment.