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Video Quality Research
Improved Techniques that Measure Video Quality
Why Tools are Needed?
There are three ways to measure video quality:
- Look at a test signal
- Ask a person's opinion of a video
- Use a computer algorithm
Test signals were an effective way to measure video quality in the days of analog television. For example, the camera focused on a picture of wide and narrow lines. Video quality was measured by finding the narrowest line on a television monitor. This does not work for modern digital systems.
Asking a person's opinion of video-also known as subjective testing-is by far the most accurate way to measure video quality. The cost and the time required are often a problem. For example, industry needs rapid feedback while fine tuning a new product.
An objective video quality model is a computer algorithm that attempts to predict human perception of video quality. This is difficult to do well. A computer algorithm tries to imitate human perception, object recognition and judgment.
To be accurate, digital video quality measurements have to be based on perceived picture quality and have to be made in-service using the actual video being sent by the users of the digital video system. The primary reason for these requirements is that the performance of digital video systems is variable and depends upon the dynamic characteristics of both the input video (e.g., spatial detail, motion) and the digital transmission system (e.g., bit-rate, error-rate). Click here for more reasons why new video quality metrics are needed.
To address the above problems, ITS developed a new measurement paradigm that is based upon extraction and comparison of low bandwidth perception-based features (e.g., edges, motion) that can be easily communicated throughout the broadcast network. This measurement paradigm has received three U.S. patents, was adopted as an ANSI standard in 1996 (ANSI T1.801.03-1996) and revised in 2003 (ANSI T1.801.03-2003), was included in two International Telecommunication Union (ITU) Recommendations in 2004 (ITU-T Recommendation J.144 and ITU-R Recommendation BT.1683), and is being used by organizations worldwide. This measurement paradigm is known internationally as "reduced-reference" video quality measurements (see International Telecommunications Union, Telecommunication Standardization Sector, ITU-T Recommendation J.143, "User requirements for objective perceptual video quality measurements in digital cable television"). This ITS-developed methodology has been extensively tested on a wide range of video systems and bit rates including video teleconferencing, MPEG (1, 2, and 4), DS3 (45 Mb/sec), as well as analog video systems.