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Video quality is a characteristic of video passed through a video processing system. Since the time when the first video sequence was recorded, lots of video processing systems have been designed. Different systems may have different influence on a video sequence, so video quality evaluation is a very important task. This article needs copyediting (checking for proper English spelling, grammar, usage, tone, style, and voice). ...
From analog to digital video
In the ages of analog video systems it was possible to evaluate the quality of video processing system by calculating the frequency response of some traditional test signal (for example, a collection of color bars and circles). An analog or analogue signal is any continuously variable signal. ...
Frequency response is the measure of any systems response to frequency, but is usually used in connection with electronic amplifiers and similar systems, particularly in relation to audio signals. ...
Nowadays digital video systems are intensively replacing analog ones, and evaluation methods must be changed. Performance of digital video processing system can vary powerfully and depends on dynamic characteristics of input video signal (e.g. motion, level of spatial details). That's why digital video quality must be evaluated on video sequences that can be actually received by users. Digital video is a type of video recording system that works by using a digital, rather than analog, representation of the video signal. ...
Objective video quality The objective evaluation techniques are mathematical models that successfully emulate the subjective quality assessment results, based on criteria and metrics that can be measured objectively. The objective methods are classified, according to the availability of the original video signal, which is considered to be in high quality. Therefore, they can be classified as Full Reference Methods, Reduced Reference Methods and No-Reference Methods. The most traditional way of evaluating the quality of digital video processing system (e.g. video codec like DivX, XviD) is counting of PSNR between source signal and video passed through this system. PSNR is one of objective video quality metrics - metrics that can be automatically computed by a computer program. Recently a number of more complicated and precise metrics were developed, for example VQM and SSIM. A video codec is a device or software module that enables the use of compression for digital video. ...
This article is about the video codec DivX. For the pay-per-view DVD system, see DIVX. DivX® is a video codec created by DivX, Inc. ...
XviD is an open source MPEG-4 video codec originally based on OpenDivX. XviD was started by a group of volunteer programmers after the OpenDivX source was closed in July 2001. ...
The phrase peak signal-to-noise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum value of a signal and the magnitude of background noise. ...
The Structural SIMilarity (SSIM) index is a novel method for measuring the similarity between two images. ...
All the aforementioned post-encoding objective methods may require repeating post-encoding tests in order to determine the encoding parameters that satisfy a specific level of user satisfaction, making them time consuming, complex and impractical for implementation on real commercial applications. For this reason, a lot of research has been focused on developing novel objective evaluation methods, which enable the prediction of the perceived quality level of a encoded video at a pre-encoding stage.
Subjective video quality The main goal of many objective video quality metrics is to automatically estimate user's opinion on a video processed by the system. But the best way to find out user's opinion is just to ask him! There are a lot of ways to do it; they are called “subjective video quality measurements”. Many of this methods are described in ITU-T recommendation BT.500. Their main idea is the same as in Mean Opinion Score for audio: video sequences are shown to the group of viewers and then their opinion is averaged to evaluate the quality of each video sequence, but details of testing may vary powerfully. Subjective video quality is a subjective characteristic of video quality. ...
The ITU Telecommunication Standardization Sector (ITU-T) coordinates standards for telecommunications on behalf of the International Telecommunication Union (ITU) and is based in Geneva, Switzerland. ...
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See also Quality refers to the inherent or distinctive characteristics or properties of a person, object, process or other thing. ...
Subjective video quality is a subjective characteristic of video quality. ...
A video codec is a software module that offers compression for digital video. ...
[info from searchnetworking. ...
The phrase peak signal-to-noise ratio, often abbreviated PSNR, is an engineering term for the ratio between the maximum value of a signal and the magnitude of background noise. ...
External links - Video Quality Experts Group
- University program for objective video quality measurements
- ITU-T page with recommendations on subjective video quality assessments
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