Graphics Reference
In-Depth Information
A *
B *
A
Original
B
Coded
Original
Coded
Vote N
1 sec
10 sec
1 sec
10 sec
1 sec
10 sec
1 sec
10 sec
5 sec
Time
Fig. 9.10
DSCQS basic test cell (BTC)
As shown in Fig. 9.10 , the BTC structure of the DSCQS method contains two
consecutive pairs of presentations. At first, a mid-grey screen with the letter “A”,
in the middle, is displayed for a second followed by a 10-s presentation of a
video clip—either original or impaired. Then, a mid-grey screen with the letter “B”
appears followed by a 10-s presentation of the second video clip. Similar process is
repeated during the second round of presentation by changing letters A and B to A*
and B*, instead. Finally, a message is displayed for 5 s instructing the viewers to
vote.
9.4.1.3
Training Session
The outcome of the visual tests could be highly dependent on the proper training
of the participants. In order to allow viewers to get familiarized with the testing
procedures, it is important that viewers are briefed about the testing procedures and
participate in a training session before starting subjective evaluation tests. Also, the
video clips shown for the training need to be different from those used during the
actual tests. Coding impairments should resemble those that appear on the tested
materials, though. In the training session, three BTCs (the worst quality, medium
quality and the best quality) should be included allowing viewers to know the quality
range of the test.
9.4.1.4
Viewing Environment
In the laboratory where the viewing session is being held, general internal light has
to be low and a uniform light has to be placed behind the monitor. The intensity of
the light is specified in the ITU-R BT.500 [ 11 , 14 ]. No light source has to be directed
to the screen or cause reflections. Ceiling, floor and walls of the laboratory have to be
made of non-reflecting material (e.g. carpet or velvet) and should have a color tuned
as close as possible to CIE Standard Illuminant D65 (daylight illuminant, 6500K).
The viewing room must be protected from external visual or audio pollution.
Search WWH ::




Custom Search