Information Technology Reference
In-Depth Information
Depending on the information that is made available to the algorithm,
video quality test algorithms can be divided into three categories:
1. A Full Reference (FR) algorithm has access to and makes use of the
original reference sequence for a comparison (i.e., a difference anal-
ysis). 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 process-
ing intensive.
2. A Reduced Reference (RR) algorithm uses a reduced side channel
between the sender and the receiver that is not capable of transmit-
ting the full reference signal. Instead, parameters are extracted at
the sending side that helps predict the quality at the receiving side.
RR measurements may offer reduced accuracy and represent a work-
ing compromise if bandwidth for the reference signal is limited.
3. A No Reference (NR) algorithm only uses the degraded signal for
the quality estimation and has no information of the original refer-
ence 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 does not even analyze the
decoded video on a pixel level but only works on an analysis of the
digital bit stream on an IP packet level. The measurement is conse-
quently limited to a transport stream analysis.
PEVQ is a full-reference algorithm according to the FR above and analyzes
the picture pixel-by-pixel after a temporal alignment (also referred to as
“temporal registration”) of corresponding frames of reference and test sig-
nals. PEVQ MOS results range from 1 (bad) to 5 (excellent).
In order to eliminate the effect of the encoder, we introduce the parameter
of relative PEVQ rate, reference PEVQ, and destination PEVQ. The reference
PEVQ is encoded video before the transmission compared with the original
video. The destination PEVQ is output video compared with the original
video. The destination PEVQ contains the transmission loss, so it must be
lower than the reference PEVQ. The relative PEVQ rate is destination PEVQ
over reference PEVQ. This is shown in Figure 3.17.
3.5.3 Video Quality Prediction
We did experiments with the ITU standard video. There are 18 videos and
each video tests three times. The videos are sent from a Dilithium UMTS
network analyzer (model no. FXPAG-P42G) to a 3G handset though circuit
switched network.
Based on our experiment results, the explicit expression could not fit the
data exactly. Then we tried implicit expression, it gives a good performance
