Mutsumi Ohta

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>>

Mathematical analysis of MPEG compression capability and its application to rate control

This paper presents mathematical frameworks of temporal predictive processing in the MPEG video compression standard. The coding gain is derived based on traditional prediction theories. The optimum ordering of three different picture types (I,P,B-pictures) is clarified according to the image source characteristics. A novel framework of the target bit assignment is presented with some experimental backgrounds. The solution consists of simple formulae, but provides drastic SNR gains to the conventional TM5 algorithm.

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. >

Very low bit rate video coding using arbitrarily shaped region-based motion compensation

This paper presents a novel region-based video coding algorithm for very low bit-rate transmission. A huge amount of region shape information in a conventional region-based coding does not need to be transmitted in the new approach, because it can be synchronously obtained from a reconstructed picture in both the encoder and decoder by image segmentation. Segmented region updating, which can obtain appropriate regions for motion compensated prediction, and a new bit assignment algorithm in prediction error coding are also developed. Computer simulations are carried out to evaluate the coding efficiency at 9.6 kb/s. The result indicates that the objective and subjective qualities for decoded pictures are improved compared to those for the conventional block-based method. This algorithm is significantly effective for mobile communication.

An encoder/decoder chip set for the MPEG video standard

A VLSI chip set capable of real-time MPEG (Moving Picture Experts Group) video encoding/decoding has been developed. It is composed of an inter-frame prediction chip, a transform and quantization chip, and a variable length coding chip. To make the chip set more cost effective, the MPEG algorithms are first partitioned into three blocks on the basis of their characteristics. Individual chip architectures are designed with the use of programmable DSP and application specific array approaches. A hierarchical data transmission method is introduced for use among the chips and frame memories. By using three chips, an MPEG video encounter can compress a 30-frames/s image sequence of 352 pels*240 lines. A decoder can be constructed with two chips for the same sequence.<<ETX>>

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. >

Entropy Coding for a Hybrid Scheme with Motion Compensation in Subprimary Rate Video Transmission

Entropy coding has been investigated for motion-compensated interframe (MC) prediction followed by two-dimensional discrete cosine transform (DCT) for prediction error. In particular, variable word length coding methods for motion vector and transform coefficients have been discussed assuming low bit rate such as 384 kbits/s for transmission of videoconference sequences. For motion vector information, it is advantageous to employ a one-dimensional code set common to both horizontal and vertical components of motion vectors. The code set can be obtained using a combined distribution of the two components. In order to encode transform coefficients, different methods are applied to significant and insignificant blocks. Run-length coding is adequate for representing clusters of insignificant blocks. In encoding transform coefficients in significant blocks, a zone coding method which encodes transform coefficients within a minimum area enclosing all nonzero coefficients is suitable. Simulation of video sequences shows that a combination of the coding methods described here can achieve high coding efficiency for videoconference sequences.

Focused object extraction with multiple cameras

This paper describes a novel framework for object extraction from images utilizing multiple cameras. Focused regions in images and disparities of point correspondences among multiple images are 3-D clues for the extraction. We examine the extraction of focused objects from images by these automatically acquired clues. Edges in images captured by the cameras are detected, and disparities of the edges in focused regions become the clues, called disparity keys. A focused object is extracted from an image as a set of edge intervals with the disparity keys. The falsely extracted parts can be detected by discontinuous contours of the object and recovered by contour morphing. Some experimental results under different conditions demonstrate the effectiveness and robustness of the proposed method. The method can be applied to image synthesis methods, such as synthesis/natural hybrid coding (SNHC) and to object-scalable coding in MPEG-4.

Visual text reader for virtual image communication on networks

This paper presents a media conversion system from text to video, which can be used as a virtual image communication tool over narrow-band networks. The proposed system analyzes a plain text, such as e-mail, and generates a video sequence for a humans bust shot which includes actions and facial expressions related to the contents. The voice sounds are also generated using text-to-speech system. Both video and voice are synchronized, so that video-phone like communication is available without any additional information out of the original text.

Entropy coding for wavelet transform of image and its application for motion picture coding

Motion picture wavelet coding is investigated. Wavelet coding is expected to be a next generation transform coding, because it can reduce blocking effect and mosquito noise, which are the major sources of image quality degradation in conventional transform coding methods. Entropy coding of wavelet coefficients is first discussed, then a blockless motion compensated adaptive inter/intra-frame prediction method is proposed for motion picture wavelet coding. Coding efficiency is evaluated by simulation. The proposed techniques improve subjective quality of decoded pictures.