To: Steve Fancy who wrote (43315 ) 7/24/1999 11:51:00 AM From: John Rieman Respond to of 50808
MPEG-2 testing equipment................... How Good is Your DTV Signal? A New Generation of T&M Devices Are Tailored To Specific Needs By Carl Mrozek (July 23, 1999) Broadcasters, satcasters and cable operators keen on getting the biggest bang for their bits are looking to a new generation of signal evaluation and monitoring equipment in order to be sure of delivering the signal quality which consumers, especially early adopters, expect from DTV. There is also the issue of using bandwidth efficiently and cost-effectively. Indeed, by NAB '99, more than a few manufacturers had stepped up to the plate to deliver the signal test and evaluation gear needed for the full range of DTV applications. One such device is the PAR by Snell & Wilcox, which is touted as "a powerful new method of assessing MPEG artifacts that can degrade picture quality." PAR, which stands for Picture Appraisal Rating, looks for artifacts within the bitstream with the help of an algorythmn that provides a numerical assessment of potential MPEG artifacts to be derived. In short, it "provides an estimate of the likely picture quality of a decoded MPEG-2 video bitstream," according to PAR developer, Michael Knee. Unlike some other T&M devices, PAR provides a rating independent of the source video quality. "It is single-ended in that it doesn't reference the source picture input to the encoder," Knee explained. "The algorythmn was derived from a large inventory of images, sequences and coding modes. Our tests have shown a strong correlation (.94) between PAR and a well known objective quality measure without access to the source video. It is especially useful for automatic, single-ended monitoring of MPEG-2 video coding performance. It is immune to conventional picture defects like like noise, film grain, decoding artifacts etc." Snell and Wilcox also unveiled a multi-function MPEG Analyzer, the MVA200, designed for studying MPEG transport streams down to the macro-block level. The MVA200 assesses in detail the performance of any MPEG encoder or decoder and can also be used to monitor and optimize the performance of components of the transmission system in the field. "It enables inspection of the structure of a transport stream and can decode a given program within it," according to Snell & Wilcox sources. "It can simultaneously analyze how the video stream was encoded down to the macro-block and even DCT block levels. It can also operate in conjunction with PAR to guage the effect of MPEG artifcacts in a compressed signal and to pinpoint where picture quality values fall below a defined level." Another innovative assessment device, the Picture Quality Analyzer (PQA), is the product of a long term collaboration between Tektronix and the Sarnoff Corp. The system, is touted as "the only objective picture quality measurement tool that actually looks at video, before and after processing," stated Tektronix marketing manager, Bruce McPherran. "The PQA200 analyzes picture quality using objective criteria which replicate subjective human visual assessment." More................................tvbroadcast.com