Reference Category

reference: https://en.wikipedia.org/wiki/PEVQ

Depending on the information that is made available to the algorithm, video quality test algorithms can be divided into three categories:

A “Full Reference” (FR) algorithm has access to and makes use of the original reference sequence for a comparison (i.e. a difference analysis). It can compare each pixel of the reference sequence to each corresponding pixel of the degraded sequence. FR measurements deliver the highest accuracy and repeatability but tend to be processing intensive.

A “Reduced Reference” (RR) algorithm uses a reduced side channel between the sender and the receiver which is not capable of transmitting the full reference signal. Instead, parameters are extracted at the sending side which help predicting the quality at the receiving side. RR measurements may offer reduced accuracy and represent a working compromise if bandwidth for the reference signal is limited.

A “No Reference” (NR) algorithm only uses the degraded signal for the quality estimation and has no information of the original reference sequence. NR algorithms are low accuracy estimates, only, as the originating quality of the source reference is completely unknown. A common variant of NR algorithms don't even analyze the decoded video on a pixel level but work on an analysis of the digital bit stream on an IP packet level, only. The measurement is consequently limited to a transport stream analysis.

PEVQ is full-reference algorithm and analyzes the picture pixel-by-pixel after a temporal alignment (also referred to as 'temporal registration') of corresponding frames of reference and test signal. PEVQ MOS results range from 1 (bad) to 5 (excellent).