1、Rec. ITU-R BT.1127 1RECOMMENDATION ITU-R BT.1127RELATIVE QUALITY REQUIREMENTS OF TELEVISION BROADCAST SYSTEMS(Question ITU-R 42/11)(1994)(1994)Rec. ITU-R BT.1127The ITU Radiocommunication Assembly,consideringa) that there is considerable discussion throughout the world on quality requirements of hig
2、h definition television,enhanced definition television, standard definition television, and limited definition television;b) that it may assist users in evaluating an appropriate system or systems if there are guidelines on the relativequality requirements of such broadcast systems,recommends1. that
3、 the quality requirements applicable to high definition, enhanced definition, standard definition, and limiteddefinition television are specified by a quality-space representation associated with design viewing distances inaccordance with Annex 1.ANNEX 1The relative quality requirements of televisio
4、n broadcast systemsThe ITU-R has considered alternative means of classifying television systems as a tool for decision makingand to assist studies. Having a well-defined way to describe the systems is a necessary prerequisite to classification.The most practical approach seems to be via a quality-sp
5、ace representation, of the kind shown in Fig. 1. Thesystems will have many facets; basic picture quality, transmission ruggedness, sound capacity etc. However, the corefeature, which can be used to best describe and delineate systems, and agreed criteria, is probably associated with basicpicture qua
6、lity.1. Example of the classification of television systems1.1 High definition televisionHDTV systems are described in Report ITU-R BT.801 as those systems which are essentially transparent to abi-dimensional representation of the real world, when the picture is seen at three times the height of the
7、 screen (3 H).There is no unique psycho-physical basis for translating this definition into quantitative subjective assessment terms.However, this Recommendation proposes that this can be interpreted to mean that subjective assessment results shouldalways fall into the “excellent” band in evaluation
8、s using the double stimulus continuous quality scale method asdescribed in Recommendation ITU-R BT.500. Quality evaluation results should include compensation for the residualerror of the reference. The quality (and therefore definition of HDTV) could lie in a requirement for the quality to bealways
9、 in this (excellent) band.2 Rec. ITU-R BT.11271.2 Enhanced definition televisionEDTV systems can be classified as a system capable of results in the excellent band when the picture is seen ata distance of four times the height of the screen (4 H) as shown in Fig. 1.3 H 4 H 5 H 6 H 7 H 8 H10080604020
10、3 H 4 H 5 H 6 H 7 H 8 H(16:9)(1)(16:9)(1)(4:3) (4:3)D01FIGURE 1Characterization of broadcast systems by design viewing distance and picture quality*ExcellentGoodFairPoorBadViewing distanceHDTV EDTV SDTV LDTVStudies carried out by Cablelabs in the United States of America describe viewer reaction whe
11、n TV pictures transmitted in an aspect ratio of 4:3 are reproduced in various forms on a 16:9 display.(1)*To be confirmed by future experiments.FIGURE 1/BT.1127.D01 = 13 CM1.3 Standard definition televisionIt is proposed that standard definition television (625/525-line) systems can be characterized
12、 by qualityrequirements associated with a viewing distance of 6 H.1.4 Limited definition televisionIt is proposed that limited definition television systems can be characterized by quality requirements associatedwith a viewing distance of 8 H.2. Design viewing distance and preferred viewing distance
13、The design viewing distance (DVD) is the distance at which the subjective assessment of the system should beperformed. Figure 1 shows the partitioning in terms of DVD for the quality levels described above.Associated with this classification of systems by quality and DVD, it may be helpful to be awa
14、re of therelationship between preferred viewing distance (PVD) and screen size. Studies show that PVD is related to the degreeof motion, the absolute eye-screen distance, screen size and programme content among other factors. Figure 2 shows theresults of studies carried out in Italy. These results a
15、re in close agreement with those obtained from similar studiescarried out in the United States of America by SMPTE. Further studies may indicate that the PVD could differ to thosein Fig. 2 due to viewing conditions and experiences in different countries.Rec. ITU-R BT.1127 3Therefore, both concepts s
16、hould be combined to ensure the fair evaluation of the systems concerned, and for afixed PVD, the size of the display used for evaluation using the methodology described in Recommen-dation ITU-R BT.500 should be enlarged to meet the required DVD, if possible.1075438342817123 H 4 H 5 H 6 H 7 H 8 HD02FIGURE 2Preferred viewing distance relationship to 16:9 screen size.The experiments used high definition sources, and areaveraged for a range of programme materialScreen diagonal(in)Preferred viewing distance StillpictureMovingpictureFIGURE 2/BT.1127.D02 = 9.5 CM_
