Showing papers on "Video quality published in 1990"

N-Way Conferencing with Packet Video

Abstract: : Packet switching technology promises to allow improvement of video quality by efficiently supporting variable-rate video coding. Its inherent multiplexing of multiple streams also allows more efficient multi-destination delivery for N-way conferencing. However, most commercial video codecs are designed to work with circuits, not packets, in part because these benefits are accompanied by some problems. This paper describes a packet video system implementation in which commercial codecs were adapted to exploit the benefits of packet switching while addressing the problems as follows: 1) clock synchronization was obviated by asynchronous operation; 2) delay was reduced by bandwidth reservation and fast packet forwarding; and 3) packet loss was reduced by bandwidth reservation and forward error correction. An overview of the system is followed by sections addressing each of the problems and benefits, plus future directions for expansion of the system.

Features for automated quality assessment of digitally transmitted video

Abstract: This report describes an automated method of video quality assessment based on extraction and classification of features from sampled input and output video. The first subsystem of the automated video quality measurement system is the feature extraction subsystem. Features are extracted from the sampled video that quantify many of the distortions present in modern digital compression and transmission systems. The feature measurements may then be injected into a quality classification subsystem which will determine the overall quality rating of the video. This report discusses the first subsystem of the automated video quality assessment system, namely the feature extraction subsystem. The measurement techniques used to extract a number of useful features are discussed in detail. Results are presented using sampled video teleconferencing data that contained common video compression artifacts.

Video quality gradient measures for digital networks

Abstract: Two of the most significant video quality degradations produced by digital compression in codecs are image blurring and distortion of edges in areas of motion. These degradations become more evident at reduced transmission rates. Two objective measures of video quality, one based on Laplacian and the other on Sobel gradient operators, are proposed. They are validated with desktop video teleconferencing (VTC) data for digital networks with sequences containing significant motion and complex detail. The measured results are compared over a range of transmission bit rates. The sensitivity and reliability of the measures are enhanced by determining the optimum Gray level thresholds for computing the measures. Both measures correlate well with transmission rate and subjective opinion of the video quality, particularly for blurring. >

Video audio multiplex system

Abstract: PURPOSE:To improve the quality of video image by assigning the transmission ratio of video and audio data in response to the presence of audio data. CONSTITUTION:An audio data generating section 2 detects the presence of the audio data, a transmission controller 3 sends a coded clock to a video data generating section 1 and an audio data generating section 2 depending on the data and a multiplex section 4 uses a multiplex control clock from the transmission controller 3 so as to multiplex the video data and the audio data. Then a bit assignment signal BAS generated from the transmission controller 3 is changed corresponding to the presence of the audio data and the changed signal is multiplexed by a multiplex section 5 and the resulting signal is sent to a receiver side. The receiver side varies the decoded clock of the video output generating section 10 and the audio output generating section 11 to decode the video data and the audio data. Thus, only the video information is sent in the absence of the audio data to improve the video quality.

Digital video on fiber: the Heathrow system

Abstract: Over the last 50 years residential video has evolved spectacularly in terms of both displayed signal quality and viewer choice. Fiber optic transmission, having brought the benefits of all-digital transport to the interoffice and long haul telecommunications networks, is now poised for a major deployment in the loop plant, which could aid further the evolution of video quality and choice. In 1987 Northern Telecom and Bell South decided to incorporate video into the fiber access system to be deployed in Heathrow, near Orlando, FL. This system was intended to provide design experience in fiber access technologies and to gain field experience in planning, installing, commissioning, and maintaining fiber based residential systems and to explore some of the resultant service opportunities. The Heathrow fiber access system provides subscribers with digital voice, data, and video services from the central office, as shown in Fig. 1.