Showing papers on "Video quality published in 1991"

Motion-compensated video coding with adaptive perceptual quantization

Abstract: The authors address the problem of adapting the Motion Picture Experts Group (MPEG) quantizer for scenes of different complexity (at bit rates around 1 Mb/s), such that the perceptual quality of the reconstructed video is optimized. Adaptive quantisation techniques conforming to the MPEG syntax can significantly improve the performance of the encoder. The authors concentrate on a one-pass causal scheme to limit the complexity of the encoder. The system employs prestored models for perceptual quality and a bit rate that have been experimentally derived. A framework is provided for determining these models as well as adapting them to locally varying scene characteristics. The variance of an 8*8 (luminance) block is basic to the techniques developed. Following standard practice, it is defined as the average of the square of the deviations of the pixels in the block from the mean pixel value. >

Objective quality assessment of digitally transmitted video

Abstract: The authors discuss an automated, objective video quality measurement system being developed for use in measuring end-to-end user performance. The method is based on extraction and classification of features from sampled input and output video. The extracted features quantify many of the distortions present in modern digital compression and transmission systems. These distortions include video compression artifacts resulting from spatial compression (blocking, edge blurring/smearing, etc.) and temporal compression (image persistence, jerky motion, etc.). Since the quality of the motion and still portions of a video scene can differ dramatically, an algorithm that segments each video frame into motion and still parts has been developed. >

The development of objective video quality measures that emulate human perception

Abstract: A method for deriving an objective video quality metric that emulates the human video quality metric is described. The objective metric comprises a family of measurements that quantify spatial, temporal, luminance, and chrominance distortions, followed by a prediction algorithm. The intent is that the derived metric will work well over a wide range of digital and analog video transmission and storage technologies. After describing the need for these measures, a detailed description of the derivation process and some preliminary results are given. >

MPEG (moving pictures expert group) video compression algorithm: a review

Abstract: A video coding technique aimed at compression of video and its associated audio at about 1.5 Mbits/s has been developed by the Moving Pictures Expert Group (MPEG-Video). The Moving Pictures Expert Group is part of the ISO-IEC JTC1/SC2/WG11, an organization responsible for the standardization of coded representation of video and audio for information systems. The video compression technique developed by MPEG covers many applications from interactive systems on CD-ROM to delivery of video information over telecommunications networks. The MPEG video compression algorithm relies on two basic techniques: block based motion compensation for the reduction of the temporal redundancy and transform domain based compression for the reduction of spatial redundancy. Motion compensation techniques are applied with both predictive and interpolative techniques. The prediction error signal is further compressed with spatial redundancy reduction (DCT). The quality of the compressed video with the MPEG algorithm at about 1.5 Mbits/s has been compared to that of consumer grade VCR's. The quality, cost and features of the MPEG video algorithm make it directly applicable to personal computers and workstation thus allowing the development of many new applications integrating video, sound, images, text and graphics.

The development and correlation of objective and subjective video quality measures

Abstract: The authors describe a method for deriving objective measurements of video quality that agree with the human perception of video quality. The development process presented is based on three components. First, a wide-ranging library of video screens is digitized and processed. The second component involves the collection of viewer quality ratings for this same video library. This results in a set of subjective data. The final component of the process is a simultaneous statistical analysis of the subjective and objective data sets. The authors focus on the second component of the process. The facility used to gather viewer quality ratings, the Institute for Telecommunication Sciences (ITS) video viewing laboratory, is described. The test methodology is presented, along with a discussion of the selection of video scenes for the tests. Plans for the integration of subjective and objective data sets are considered. >

Gradient measures of compressed video teleconferencing quality

Abstract: Two objective measures, computed from received digital images, that can be used to assess video quality are proposed. These measures, based on Laplacian and Sobel gradient operators, are developed and applied to video teleconferencing (VTC) sequences of live desktop scenes and conference table scenes with motion present. The measured results are then 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 are shown to monotonically increase with transmission rate and corresponding illustrative subjective evaluation of the images. These measures have been proposed for possible inclusion into a draft National VTC Standard under development in the ANSI T1Q1.5 teleconferencing standards group. >

Video encoding multiplex transmission system

Abstract: PURPOSE:To improve transmission efficiency and a video quality by controlling respective encoding by means of the sum of a generation information quantity by means of the encoding of video signals at the time of encoding and multiplex- transmitting the video signals of plural channels. CONSTITUTION:A video signal A is variable length-encoded in a video encoding part 1 and is outputted as encoding information. An information quantity measurement part 4 measures the information quantity of encoded information concerned and outputs it to an information quantity control part 7. The encoded information is multiplexed in a multiplex transmission part 8 together with encoded information of the other video signals B and C, and they are transmitted to a transmission line 9. The information quantity control part 7 controls respective video encoding parts 1-3 by the information quantity measured in respective information quantity measurement parts 4-6. Control is executed when the sum of the information quantity of repective video signals exceeds a set point, for example.

Analysis of optimum-frame-rate in low-bit-rate video coding

Abstract: We analyze frame rates in low bit rate video coding and show that an optimal frame rate can betheoretically obtained. In order to achieve an optimum balance between coded picture quality andmotion smoothness, a frame rate has to be selected which is appropriate to parameters such as coding scheme, property of the video signals and coding bit rate. In this paper, coding distortion measured by mean square error due to quantization is analyzed by modeling video signals, and it is shown that theframe rate can be uniquely optimized. The result of this analysis is compared with the results ofcomputer simulation. In addition, the relation between this analysis and the subjective evaluation is described. 1. INTRODUCTIONVisual communication is expected to prevail increasingly in future thanks to the rapid development of digital networks such as Integrated Services Digital Network (ISDN). In particular, TV conference I video phone has been one of the major media of communication since the

Correlation Between ITS Objective Measures and Subjective Video Quality: Preliminary Results on a Set of 15 Scenes

Abstract: Presents preliminary results on the objective to subjective quality correlation for a set of 5 test scenes passed through three systems (NTSC, VHS, and DS1 MPEG coding). One objective metric that correlates well with subjective quality quantifies the amount of false or extra edges that have been added to the output video. There appears to be some advantages to applying the metric separately to the still and motion portions of the video.

Bit-rate control algorithm on video packet coding and its characteristics

Abstract: A bit-rate control method based on a hybrid coding algorithm is proposed for packet video coding. Three types of bit-rate control modes, the constant bit-rate mode, the average bit-rate control mode and the free bit-rate mode, are investigated. According to the opinion test the latter two modes have an advantage in video quality over the constant bit-rate mode. A teleconference terminal, which includes this video codec, audio codec and packet adaptor, is implemented in actual hardware on High-speed Packet Switching system. On this system, video information are transmitted in UI frame (a packet format in X.25 protocol) at 64 K ∼ 800 Kbit/s.