Satoshi Nogaki

An overlapped block motion compensation for high quality motion picture coding

An overlapped block motion compensation scheme, which is especially suitable for hybrid coding schemes combine with overlapped transforms, is described. Motion compensation is achieved using enlarged and overlapped blocks. When motion estimation is executed, a window function operates on the prediction error signals. The power of the resulting signal is calculated and used for motion vector evaluation. When motion-compensated prediction is executed, the same window function operates on the prediction signals. The total prediction signal is generated by summing up all the block signals obtained. With this scheme, prediction signals without blocking edges are obtained. The mean square error (MSE) of the prediction error signal is reduced about 19%, and FFT analysis results show that the coefficient power in the frequency domain is concentrated in the lower frequency part. This indicates higher coding efficiency for the overlapped transforms, and for conventional block based transforms as well.<<ETX>>

Hybrid picture coding with wavelet transform and overlapped motion-compensated interframe prediction coding

A novel video coding scheme using an orthonormal wavelet transform is proposed. The wavelet transform is used in a motion compensated interframe coder in which a blockless motion compensation technique is employed to increase efficiency of wavelet transform coding. A new scanning method for wavelet coefficients is also proposed which is rather different from subband coding. Simulation work is carried out to evaluate the proposed coding method. Significant improvement in subjective quality is obtained over that obtained with conventional hybrid coding methods that use blockwise motion compensation and DCT. Some improvement has also been realized in the signal to noise ratio. Although wavelet coding is still in its early stages of development, it appears to hold great promise for motion picture coding. >

A wavelet codec with overlapped motion compensation for very low bit-rate environment

The paper describes theories on overlapped motion compensation and their applications to a wavelet codec aimed for the very low bit-rate environment below 64 kb/s. The theories are concerned with the evaluation of prediction efficiency improved by overlapped motion compensation and also its smoothing effect on the discontinuities at block boundaries encountered when motion vectors do not coincide among neighboring blocks. They contribute to determine the optimum window shape for overlapped motion compensation in a developed wavelet codec, which suffers from reduction of coding efficiency when there are such discontinuities in a signal to be transformed. Regarding the wavelet codec, a new scanning method of transform coefficients and alternate use of normal and spatially-reversed basis functions for the cascaded wavelet transform are introduced. Finally, the implementation of the codec on a video image signal processor (VISP) is discussed. >

Memory compression method considering memory bandwidth for HDTV decoder LSIs

This paper proposes a frame memory compression method for an MPEG-2 Main Profile@High-Level (MP@HL) decoder LSI using Direct RambusTM DRAM (DRDRAM). The compression method is based on two-dimensional adaptive DPCM (2-D ADPCM) and is designed to achieve efficient memory access. HDTV bitstreams are decoded with a single 64 megabit (Mb) DRDRAM without subjective image quality degradation. Computer simulation is performed for ten HDTV bitstreams encoded at 22 Mbps. Simulation results show that, in the worst case, SNR loss compared to the full spec decoder is 0.71 dB for a luminance, 0.27 dB and 0.57 dB for chrominances.

A study on rate control method for MP@HL encoder with parallel encoder architecture using picture partitioning

This paper proposes rate control methods for parallel encoder architecture using picture partitioning, which is often used for MPEG-2 VIDEO Main Profile @ High Level (MP@HL) encoders. Partitioning boundaries are sometimes visible in decoded pictures because of control discontinuity. An adaptive bitrate allocation scheme is proposed to reduce the discontinuity of picture quality around partitioning boundaries. Quantizer scale (Qscale) restriction in rate control is also proposed for further improvement. Computer simulation results show that both optimum bitrate allocation and discontinuity reduction around the partitioning boundaries are achieved with the proposed methods.

A rate control method with preanalysis for real-time MPEG-2 video coding

This paper proposes a bit rate control method with a preanalysis for real-time MPEG-2 video coding. The rate control method allocates bits to pictures according to picture coding complexities obtained from the preanalysis. The bit allocation is adjusted to satisfy the VBV constraints. The method is evaluated by MPEG-2 video encoding experiments for sequences whose characteristics significantly change, such as scene changes or fade scenes. The experimental results show that the picture quality is improved by the proposed control method. The PSNR is 2 to 3 dB higher than the conventional method without a preanalysis in difficult scene periods. The method is very effective when a certain coding delay is allowed.

Load reduction methods for DTMF decoders with adaptive omission of frequency analysis

Dual-Tone Multi-Frequency (DTMF) signaling is used in telecommunication systems for dialing telephone numbers and sending commands to equipment such as interactive voice response (IVR) systems. There are two types of signalings to transmit DTMF digits: in-band and out-of-band. Since many systems use in-band signaling, equipment that uses DTMF signaling needs to support in-band signaling. Media servers that provide IVR services must process a huge number of sessions in parallel. The load of decoding in-band DTMF digits needs to be reduced to increase in the number of sessions processed by media servers. This paper presents load reduction methods with adaptive omission of frequency analysis and simulation results showing that the presented methods reduced the load of DTMF decoding by more than 50%.