Yoshiaki Shishikui

Development of 135 Mbit/s HDTV codec

Abstract The source bit-rate of HDTV is extremely high compared with that of conventional standard TV, and a bit-rate reduction will become an important matter in the digital transmission of HDTV signals using a communication satellite or the Broadband-ISDN. The authors are developing an HDTV codec based on DCT plus motion-compensated prediction at a bit-rate of 135 Mbit/s and an original sampling frequency of the studio standard. This paper outlines the technical description of this HDTV prototype codec presently being built.

Video coding with wavelet image size reduction and wavelet super resolution reconstruction

We propose a novel video coding paradigm with wavelet image size reduction and wavelet super resolution (SR) reconstruction for the pre - and post-processing of a conventional MPEG-4 advanced video coding (AVC) | H.264 codec. The proposed method features the wavelet SR reconstruction in the post-processing can ensure stability and precision by using SR reconstruction parameters which are adaptively optimized with the original image on local SR reconstruction in the pre-processing. Experimental results showed that our proposed method has a higher objectively measured peak signal-to-noise ratio and outputs images with a better subjectively evaluated appearance than the MPEG-4 AVC | H.264 codec without this paradigm.

Robust depth-map estimation from image sequences with precise camera operation parameters

The depth-map of a scene conveys the fundamental information that is extremely useful for object segmentation, compact representation of videos, etc. We present an algorithm for robust depth-map estimation from image sequences with precise camera operation parameters. This algorithm exploits precise camera operation parameters to find correspondence points among multiple frames of an image sequence of a static scene. Our algorithm is able to deal with arbitrary camera movement. The experimental results show significant improvement in the accuracy of depth-maps compared with the conventional two-frame matching method.

Novel video coding paradigm with reduction/restoration processes

To optimally design distortions in lossy video coding, we propose the use of a novel coding paradigm with adaptive nonlinear transforms as pre/post-processors of a conventional video codec. The preprocessor decimates less important pixels based on an image analysis. A conventional video encoder such as MPEG-4 AVC/H.264 further eliminates the redundancy of the decimated images. On the decoder side, the postprocessor restores small decoded images of the conventional decoder to the original resolution using an inverse mapping including a super-resolution technique that uses a priori knowledge on the decimation in the preprocessing. Results of the experiments showed the proposed coding scheme poses distortion that has a more straightforward appearance than that of a directly encoded/decoded image by a sole conventional H.264 codec.

A high-precision camera operation parameter measurement system and its application to image motion inferring

In this paper we describe a high-precision camera operation parameter measurement system and apply it to image motion inferring. First, we outline the implemented system which is designed to provide camera operation parameters with a high precision required for image coding applications. Second, we calibrate the camera lens to determine its exact optical properties. A new technique is employed to improve the accuracy of internal camera parameters obtained from a commonly used algorithm. Last, we apply the pan, tilt and zoom operation parameters measured by the system to infer image motion. The experimental results show that the inferred motion coincides with the actual motion very closely, with an error of less than 0.5 pixel even for large motion up to 80 pixels.

Digital bit-rate reduction systems of HDTV

A study of digital coding of an HDTV picture appropriate for use with contribution links is described. Three coding methods, which are based on differential pulse-code modulation (DPCM), discrete transform cosine (DCT), and vector quantization (VQ) techniques, respectively, are proposed and evaluated with the aid of computer simulation. It has been found that all three methods provide good picture quality without perceptible degradation when used at a bit rate of twice the H4 rate. The vector-quantization-based method is the most hopeful candidate for transmission at a rate of H4.<<ETX>>

Analysis of overlapped block motion compensation based on a statistical motion distribution model

Overlapped block motion compensation (OBMC) has been shown to provide reduced prediction errors as well as reduced blocking artifacts compared with the conventional non-overlapped block motion compensation (NOBMC). However, there is no satisfactory theoretical basis that clearly interprets why OBMC can reduce prediction errors. We present a theoretical analysis of OBMC based on a novel statistical motion distribution model. Our analysis proves theoretically that prediction errors increase towards block boundaries and that OBMC has an error reduction and equalization property, with the errors being more reduced at block boundaries than at block centers. The analytical results are justified by empirical experiments with typical image sequences.

An HDTV Coding Scheme using Adaptive-Dimension DCT

Coding Schemes using motion compensation and DCT are generally used for digital transmission systems of HDTV signals. In these schemes, a picture quality degradation known as mosquito-noise is sometimes a serious problem. This kind of degradation is a vital issue for HDTV which is characterized by high picture quality. In this paper, a new coding scheme named adaptive-dimension DCT is proposed; its effectiveness is explained from both theoretical and experimental viewpoints. This scheme is quite easy to implement, and suitable for HDTV coding systems that require high-speed signal processing.

A study on introduction of PSD model for field merged signal and its analysis

This paper describes a theoretical model of the power spectrum density (PSD) for a field-merged frame signal, and compares the efficiency between the field based coding, and frame-based coding that uses the field-merged signal. Recently, for the coding of interlace-scanned television signals, the field-merged signal is also used as an input signal to spatial coding process. However, the nature of PSD, which is an important basis for a high efficiency coding, is not clarified enough for the field-merged signal. For instance, there is no assurance of the optimality of the conventional techniques that are applied to the field-merged signal. The author has introduced a theoretical PSD model for the field-merged signal, and has clarified its properties in relation to the motion of the image. Using the model, the performance of frame based-coding has been calculated.