1、Rec. ITU-R BT.811-1 1RECOMMENDATION ITU-R BT.811-1THE SUBJECTIVE ASSESSMENT OF ENHANCED PALAND SECAM SYSTEMS(Question ITU-R 211/11)(1992-1994)Rec. ITU-R BT.811-1The ITU Radiocommunication Assembly,consideringa) that many proposals for improving the quality of PAL and SECAM systems are under discussi
2、on, some ofwhich concern only the receiver (e.g. doubling of the frame-rate) while others involve a considerable change of theemission system;b) that for enhanced PAL and SECAM emission formats, separate evaluations will be necessary for the enhancedpicture and for the compatible picture;c) that the
3、re will be a need to evaluate, for both the enhanced and compatible picture, the following: basic picture quality; failure characteristics; echo behaviour; and susceptibility to interference,recommends1. that for the evaluation of basic picture quality for enhanced PAL and SECAM emission systems, th
4、e double-stimulus continuous quality-scale method is recommended for both kinds of assessments (enhanced and compatiblepictures) (see Recommendation ITU-R BT.500).As a reference it is recommended to use: a 4:2:2 picture with an aspect ratio of 16:9 for the enhanced picture; a full-screen PAL or SECA
5、M picture for the compatible picture, if necessary produced by a pan-and-scantechnique.Test sequences should be critical but not unduly so with respect to the intended enhancements and possibledegradations mentioned above. The increasing use of computer graphics and video effects should also be take
6、n intoconsideration. Some sequences should include fine detailed structures and edges, which could cause cross effects inthe PAL or SECAM formats. Still and moving picture sequences are required;2. that for the evaluation of failure characteristics, echo behaviour and interference behaviour, the dou
7、ble-stimulus impairment scale method (Recommendation ITU-R BT.500) should be used for the tests of the enhanced andthe compatible picture. It is recommended to use the source references as in 1 above;3. that, for subjective assessments, the general viewing conditions be as given in Recommendation IT
8、U-RBT.500, while specific viewing conditions be as given in Table 1;4. that the quality and processing capabilities of the production format used as a source for the enhanced PALor SECAM pictures should also be evaluated.2 Rec. ITU-R BT.811-1TABLE 1Specific viewing conditions for subjective assessme
9、nts of enhancedPAL and SECAM systemsCondition Item Valuesa Ratio of viewing distance to picture height4 H and 6 H for the enhanced picture(1)4 H and 6 H for the compatible picture(2)b Peak luminance of the display 70 cd/m2c Viewing angle subtended by that part ofthe background that satisfies specifi
10、cations 43 high 57 wided Displays For the 16:9 enhanced picture, display should behigh quality with a screen size of 28 in (72 cm)or greaterFor the 4:3 compatible image, display should behigh quality with a screen size of 22 in (56 cm)or greater(1)A distance of four times the height of the picture (
11、4 H) is the preferred distance, but using assessors at 6 H also isacceptable, provided the results are given separately.(2)6 H is the preferred distance, but using assessors at 4 H also is acceptable, provided the results are given separately.ANNEX 1Explanatory noteThe fair evaluation of enhanced te
12、levision systems, applying the assessment methodology described inRecommendation ITU-R BT.500, requires that particular attention be paid to the following items (among others): choice and display of the reference to assess the basic quality of the enhanced system under evaluation; choice and display
13、 of the reference to assess the quality if the compatible picture is viewed with a conven-tional television system (different aspect ratio, etc.).For enhanced systems with a 16:9 aspect ratio, assessment of the compatible picture, usually with a letter-boxpresentation, implies comparison against a r
14、eference signal with a 4:3 aspect ratio. The comparison of signals withdifferent aspect ratios requires special measures; the assessment should use the same 4:3 display and the samepresentation arrangement.Two possible alternative arrangements may be considered: presentation of the compatible pictur
15、e on a 4:3 display in letter-box format and of the reference 16:9source on a 4:3 display in letter-box format by anamorphic scan conversion to letter-box form; or presentation of the compatible picture on a 4:3 display with the side panels eliminated and the imagemagnified to the full height of the screen and of the reference 16:9 source on a 4:3 display in full heightby eliminating the side panels and displaying in normal height.In both cases, two 4:3 monitors with different vertical scanning are needed. Therefore, extreme care should beexercised in matching the two monitors._
