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Rec. ITU-R BT.500-11 1
RECOMMENDATION ITU-R BT.500-11
Methodology for the subjective assessment of the
quality of television pictures
(Question ITU-R 211/11)
(1974-1978-1982-1986-1990-1992-1994-1995-1998-1998-2000-2002)
The ITU Radiocommunication Assembly,
considering
a) that a large amount of information has been collected about the methods used in various
laboratories for the assessment of picture quality;
b) that examination of these methods shows that there exists a considerable measure of
agreement between the different laboratories about a number of aspects of the tests;
c) that the adoption of standardized methods is of importance in the exchange of information
between various laboratories;
d) that routine or operational assessments of picture quality and/or impairments using a
five-grade quality and impairment scale made during routine or special operations by certain
supervisory engineers, can also make some use of certain aspects of the methods recommended for
laboratory assessments;
e) that the introduction of new kinds of television signal processing such as digital coding and
bit-rate reduction, new kinds of television signals using time-multiplexed components and, possibly,
new services such as enhanced television and HDTV may require changes in the methods of
making subjective assessments;
f) that the introduction of such processing, signals and services, will increase the likelihood
that the performance of each section of the signal chain will be conditioned by processes carried out
in previous parts of the chain,
recommends
1 that the general methods of test, the grading scales and the viewing conditions for the
assessment of picture quality, described in the following Annexes should be used for laboratory
experiments and whenever possible for operational assessments;
2 that, in the near future and notwithstanding the existence of alternative methods and the
development of new methods, those described in § 4 and 5 of Annex 1 to this Recommendation
should be used when possible; and
3 that, in view of the importance of establishing the basis of subjective assessments, the
fullest descriptions possible of test configurations, test materials, observers, and methods should be
provided in all test reports;
4 that, in order to facilitate the exchange of information between different laboratories, the
collected data should be processed in accordance with the statistical techniques detailed in Annex 2
to this Recommendation.
2 Rec. ITU-R BT.500-11
NOTE 1 – Information on subjective assessment methods for establishing the performance of
television systems is given in Annex 1.
NOTE 2 – Description of statistical techniques for the processing of the data collected during the
subjective tests is given in Annex 2.
ANNEX 1
Description of assessment methods
1 Introduction
Subjective assessment methods are used to establish the performance of television systems using
measurements that more directly anticipate the reactions of those who might view the systems
tested. In this regard, it is understood that it may not be possible to fully characterize system
performance by objective means; consequently, it is necessary to supplement objective
measurements with subjective measurements.
In general, there are two classes of subjective assessments. First, there are assessments that establish
the performance of systems under optimum conditions. These typically are called quality
assessments. Second, there are assessments that establish the ability of systems to retain quality
under non-optimum conditions that relate to transmission or emission. These typically are called
impairment assessments.
To conduct appropriate subjective assessments, it is first necessary to select from the different
options available those that best suit the objectives and circumstances of the assessment problem at
hand. To help in this task, after the general features reported in § 2, some information is given in § 3
on the assessment problems addressed by each method. Then, the two main recommended methods
are detailed in § 4 and 5. Finally, general information on alternative methods under study is reported
in § 6.
The purpose of this Annex is limited to the detailed description of the assessment methods. The
choice of the most appropriate method is nevertheless dependent on the service objectives the
system under test aims at. The complete evaluation procedures of specific applications are therefore
reported in other ITU-R Recommendations.
2 Common features
General viewing conditions for subjective assessments are given. Specific viewing conditions, for
subjective assessments of specific systems, are given in the related Recommendations.
2.1 General viewing conditions
Different environments with different viewing conditions are described.
The laboratory viewing environment is intended to provide critical conditions to check systems.
General viewing conditions for subjective assessments in the laboratory environment are given in
§ 2.1.1.
The home viewing environment is intended to provide a means to evaluate quality at the consumer
side of the TV chain. General viewing conditions in § 2.1.2 reproduce a near to home environment.
Rec. ITU-R BT.500-11 3
These parameters have been selected to define an environment slightly more critical than the typical
home viewing situations.
Some aspects relating to the monitors resolution and contrast are discussed.
2.1.1 Laboratory environment
2.1.1.1 General viewing conditions for subjective assessments in laboratory environment
The assessors’ viewing conditions should be arranged as follows:
a) Ratio of luminance of inactive screen to peak luminance: ≤ 0.02
b) Ratio of the luminance of the screen, when displaying
only black level in a completely dark room, to that
corresponding to peak white: ≈ 0.01
c) Display brightness and contrast: set up via PLUGE (see
Recommendations
ITU-R BT.814 and
ITU-R BT.815)
d) Maximum observation angle relative to the normal (this number
applies to CRT displays, whereas the appropriate numbers for
other displays are under study): 30°
e) Ratio of luminance of background behind picture monitor to
peak luminance of picture: ≈ 0.15
f) Chromaticity of background: D
65
g) Other room illumination: low
2.1.2 Home environment
2.1.2.1 General viewing conditions for subjective assessments in home environment
a) Ratio of luminance of inactive screen to peak luminance: ≤ 0.02 (see § 2.1.4)
b) Display brightness and contrast: set up via PLUGE (see
Recommendations
ITU-R BT.818 and
ITU-R BT.815)
c) Maximum observation angle relative to the normal
(this number applies to CRT displays, whereas the
appropriate numbers for other displays are under study): 30°
d) Screen size for a 4/3 format ratio: This screen size should
satisfy rules of preferred
viewing distance (PVD)
e) Screen size for a 16/9 format ratio: This screen size should
satisfy PVD rules
4 Rec. ITU-R BT.500-11
f) Monitor processing: Without digital
processing
g) Monitor resolution: See § 2.1.3
h) Peak luminance: 200 cd/m
2
i) Environmental illuminance on the screen (Incident
light from the environment falling on the screen,
should be measured perpendicularly to the screen): 200 lux
The viewing distance and the screen sizes are to be selected in order to satisfy the PVD. The PVD
(in function of the screen sizes) is shown in the following table and graph. Figures could be valid
both for SDTV and HDTV as very little difference was found.
0500-00
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
PVD for moving images
PVD (H)
Ratio of viewing distance (m) to picture height (m)
0 0.5 1 1.5 2
Screen height (m)
Screen diagonal
(in)
Screen height
(H )
PVD
4/3 ratio 16/9 ratio (m) (H )
12 15 0.18 9
15 18 0.23 8
20 24 0.30 7
29 36 0.45 6
60 73 0.91 5
> 100 > 120 > 1.53 3-4
Rec. ITU-R BT.500-11 5
This table and graph are intended to give information on the PVD and related screen sizes to be
adopted in the Recommendations for specific applications.
2.1.3 Monitor resolution
The resolution of professional monitors, equipped with professional CRTs, usually complies with
the required standards for subjective assessments in their luminance operating range.
Not all monitors can reach a 200 cd/m
2
peak luminance.
To check and report the maximum and minimum resolutions (centre and corners of the screen) at
the used luminance value might be suggested.
If consumer TV sets with consumer CRTs are used for subjective assessments, the resolution could
be inadequate, depending on the luminance value.
In this case it is strongly recommended to check and report the maximum and minimum resolutions
(centre and corners of the screen) at the used luminance value.
At present the most practical system available to subjective assessments performers, in order to
check monitors or consumer TV sets resolution, is the use of a swept test pattern electronically
generated.
A visual analysis allows to check the resolution. The visual threshold is estimated to be –12/–20 dB.
The main drawback of this system is the aliasing created by the shadow mask that makes the visual
evaluation hard, but, on the other hand, the aliasing presence indicates that the video frequency
signal exceeds the limits given by the shadow mask, which under samples the video signal.
Further studies on CRTs definition testing could be recommended.
2.1.4 Monitor contrast
Contrast could be strongly influenced by the environment illuminance.
Professional monitors CRTs seldom use technologies to improve their contrast in a high
illuminance environment, so it is possible they do not comply with the requested contrast standard
if used in a high illuminance environment.
Consumer CRTs use technologies to get a better contrast in a high illuminance environment.
To calculate the contrast of a given CRT, the screen reflection coefficient, K, of such CRT is
needed. In the best case the screen reflection coefficient is approximately K = 6%.
With a diffused environment I illuminance of 200 lux and a K = 6%, a 3.82 cd/m
2
, luminance
reflection of inactive screen areas is calculated
with the following formula:
K
I
L
reflected
π
=
With the given values, the reflected luminance (cd/m
2
) is nearly 2% of the incident illuminance
(lux).
The CRT is considered not to have mirror like reflections on the front glass, whose exact influence
on contrast is difficult to quantify because it is very dependant on lighting conditions.
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资源评论
- wangjiajingalice2014-06-21可以借鉴,不错
- ragnarok012013-05-13正是我想要的ITU-R BT 500.11,感谢
amoom
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