Hiuk Jae Shim

Wyner-Ziv video coding with side matching for improved side information

To make an encoder extremely simple by eliminating motion prediction/compensation from encoder, source coding with side information has been investigated based on the Wyner-Ziv theorem as the basic coding principle. However, the frame interpolation at decoder which is essential for redundancy elimination makes erroneous side information when the basic assumption of linear motion between frames is not satisfied. In this paper, we propose a new Wyner-Ziv video coding scheme featuring side matching in the frame interpolation to improve the side information. In the proposed scheme, Wyner-Ziv decoder compensates wrong blocks by side information using side matching and bi-directional searching. The noise reduction in side information allows the proposed algorithm to achieve coding improvements not only in bitrate but also in PSNR. Results of our experiments show improvement of PSNR up to 0.4dB.

Wyner-Ziv coding with spatio-temporal refinement based on successive turbo decoding

Arising needs for extremely simple encoder motivate investigations on distributed video coding (DVC). The Wyner-Ziv coding, one of the representative DVC schemes, reconstructs video by correcting noise on side information using channel code. Therefore, its coding performance decisively depends on the amount of noise in the side information. However it is hard for a decoder to generate good side information, especially in case that frames are less correlated., Large amount of parity bits certainly helps the decoder to correct noise but it only comes with low compression ratio. In this paper, we propose a method to enhance the quality of the side information, with incrementally transmitted parity bits from encoder. Results of our experiments have verified average PSNR gain up to 0.8 dB.

Fast inter mode decision process for HEVC encoder

In this paper, we propose a fast inter mode decision method for High Efficiency Video Coding (HEVC) in order to reduce computational complexity of its encoder. It utilizes correlated tendency of PU mode. Compared to the early termination schemes for fast mode decision already implemented in HEVC reference software, it reduces the loss of coding efficiency. Experimental results show that the proposed method decreases encoding time by about 22.5% with little increment in bit-rate. Furthermore, the proposed method shows encoding time reduction of 39.1% with only 0.8% increase of bit-rate when it is combined with existing fast methods such as early CU termination scheme.

Measurement coding for compressive imaging using a structural measuremnet matrix

Compressive imaging can acquire image signal in an under-sampled (i.e., under Nyquist rate) representation called measurement. However, measurement compression still has an essential problem in its overall rate-distortion performance. In this paper, we propose a measurement prediction method in which the best predictor is directionally selected in order to reduce the entropy of measurement to be sent. Generally, the measurement prediction usually works well with a small block while the quality of recovery is known to be better with a large block. In order to overcome this dilemma, we propose to use a structural measurement matrix with which compressive sensing is done in a small block size but recovery is performed in a large block size. In this way, both prediction and recovery are expected to be improved at the same time. Experimental results show its superiority in measurement coding amounting up to bitrate reduction by 39 %.

Deblocking filter for artifact reduction in distributed compressive video sensing

The distributed compressive video sensing (DCVS) poses itself as a very promising framework for future video coding on mobile devices due to its very low complexity at the encoder not only in sampling but also in compression. However its blocking artifacts and oscillatory artifacts especially in high-frequency components seriously degrade perceptual quality. In this paper, we try to solve both problems of the high-frequency oscillatory and blocking artifacts as a whole by a proposed deblocking filter. By differentiating those well-decoded blocks from poorly-decoded blocks using concept of reliability, the proposed method can improve DCVS framework in both objective and subjective qualities.

Fast inter sub-partition prediction unit mode decision for HEVC

In this paper, we propose a fast inter mode decision method for High Efficiency Video Coding (HEVC) in order to reduce its encoding complexity by simplifying the inter prediction unit (PU) mode decision process. Experimental results show that encoding time is reduced by 46.5% at the consequence of only 1.1% coding efficiency loss when the proposed method is jointly used with the early CU termination (ECU) method.

Motion linearity based skip decision for Wyner-Ziv coding

In this paper, we propose a SKIP decision method based on the linearity of motion in Wyner-Ziv coding structure. By comparing motion vectors of the side information with respect to each key frame, decoder evaluates quality of side information. When motion in side information is estimated as linear, a good quality of side information is expected, therefore we send the SKIP indication to encoder and as a result, parity bits of those selected blocks are saved. Moreover, if noise is small on the side information, reconstructed frame can be replaced by the side information without compromising its quality. The proposed method enhances compression performance in both bit-rate and PSNR, and our experimental result shows PSNR gain up to 1dB compared to the well-known conventional DVC codec.

DH-LZW: lossless data hiding method in LZW compression

In compressed data, there is not enough room available for data hiding, consequently many data hiding methods try to modify original data before compression. One of well-known lossless compression methods is LZW. It has been widespread due to wide use of GIF format. In spite of its reputation on compression, however, few data hiding methods are directly applicable to LZW itself. This may be due to few redundancies remained in losslessly compressed data. In this paper, we propose the DH-LZW method that embeds a certain message to source data in a lossless manner. Forced update method and an efficient data embedding scheme are proposed to be used. Finally, we show promising experimental results.

Rotation-, scaling-, and translation-robust image watermarking using Gabor kernels

In this paper, we propose a RST-robust watermarking algorithm which exploits the orientation feature of a host image by using 2D Gabor kernels. From the viewpoint of watermark detection, host images are usually regarded as noise. However, since geometric manipulations affect watermarks as well as the host images simultaneously, evaluating host image can be helpful to measure the nature of distortion. To make most use of this property, we first hierarchically find the orientation of the host image with 2D Gabor kernels and insert a modified reference pattern aligned to the estimated orientation in a selected transformed domain. Since the pattern is generated in a repetitive manner according to the orientation, in its detection step, we can simply project the signal in the direction of image orientation and average the projected value to obtain a 1-D average pattern. Finally, correlation of the 1-D projection average pattern with watermark identifies periodic peaks. Analyzed are experimental results against geometric attacks including aspect ratio changes and rotation.

Fast transform skip mode decision for HEVC screen content coding

This paper investigates a fast transform skip mode decision method which can reduce residual coding complexity of a transform skip tool for SCC (Screen Content Coding) extension of HEVC (High Efficiency Video Coding). Noticing the high tendency of transform skip mode occurring in 4×4 transform blocks in a coding unit (CU) coded as the intra block copy, the proposed fast method is designed to select either transform skip or coded block flag being zero for 4×4 blocks in a CU coded as intra block copy. Experiments verify reduction of total encoding time by average 3.0% and 4×4 transform block encoding time by 28.2% with only a slight increase of BD-rate by 0.22%. In addition, a modified transform skip mode signaling method is designed in order to minimize the coding efficiency loss due to the proposed fast mode decision. It shows reduction of total encoding time by 2.9% on average and encoding time of 4×4 transform block by 27.6% with only 0.05% BD-rate degradation.