1、 Recommendation ITU-R BT.1845-1(03/2010)Guidelines on metrics to be used when tailoring television programmes to broadcasting applications at variousimage quality levels, display sizesand aspect ratiosBT SeriesBroadcasting service(television)ii Rec. ITU-R BT.1845-1 Foreword The role of the Radiocomm
2、unication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulato
3、ry and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/
4、ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-
5、R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound)
6、 BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination betwee
7、n fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic P
8、ublication Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R BT.1845-1 1 RECOMMENDATION ITU-R BT.1845-1 Guidelines on metrics to be used when tailoring*television programmes to broadcasting
9、 applications at various image quality levels, display sizes and aspect ratios (2008-2010) Scope This Recommendation provides some guidance on the metrics relevant to the choice of image rasters that may be appropriate when tailoring television programme material to broadcasting applications which a
10、re characterized by presentation requirements different from those for which the programme was originally produced. The ITU Radiocommunication Assembly, considering a) that the typical value of the minimum angular resolution of human vision in both the vertical and horizontal directions is 1 arc-min
11、, which corresponds to the ability to discriminate detail that subtends an angle of 1 arc-min at the viewers eye, within a rather wide range of values for image contrast and mean luminance; the same may also apply to the ability of the human eye to discriminate edge transitions; b) that, consequentl
12、y, the optimal viewing distance for digital images can be taken to be the one at which the pixel pitch of the digital source image subtends an angle of 1 arc-min at the viewers eye; c) that this characteristic of the human visual acuity applies to static images, since moving images may look blurred
13、due to the limited ability of the display to portray movement, and of the human eye to follow movement on the display; d) that the static resolution of images is thus an appropriate parameter to characterize the resolution of image systems; e) that it is generally recognized that the normal reading
14、distance is about 35 cm and the closest distance to which the human eye can comfortably focus (“accommodate”) for extended periods of time (the “closest comfortable viewing distance”) can be taken to typically be 25 cm1; this has a bearing on the finest image detail that the human eye can comfortabl
15、y resolve on small *The verb “to tailor” is used in this text to indicate the post-processing operations required to adapt programme material for its presentation in broadcasting applications different from the one for which it had been originally produced, e.g. in terms of image size resolution, vi
16、ewing conditions, etc. 1Accommodation is the process by which the eye changes its focal distance to enable a clear vision of near or far objects. Generally, the eyes of very young individuals can focus on objects as close as about 8 cm. The range of accommodation, however, declines with age until, a
17、t the age of about 50, the minimal focusing distance becomes greater than the reading distance, which is about 35 cm, and the individual becomes presbyopic and needs reading glasses. For the purpose of this Recommendation we assume a closest comfortable viewing distance of 25 cm, which is closer tha
18、n the reading distance, but should still allow prolonged viewing without excessive eye fatigue. 2 Rec. ITU-R BT.1845-1 displays such as those of cellular phones, hand-held receivers and similar portable devices when they are used to display television programming; f) that consideration of the “optim
19、al viewing distance” and of the “closest comfortable viewing distance” may provide a scientific foundation to plot various image systems and display sizes in a common, static resolution space and table, based on objective technical parameter values2, further considering a) that digital television im
20、age systems for production are based on a matrix of pixels, and digital flat-panel television displays also use a presentation based on a matrix of pixels; b) that the pixel density in the presentation matrix and the way its pixels are addressed are not necessarily related to the pixel density and a
21、ddressing method used at source; consequently the source images to be displayed may need to be processed in the display, in order to re-map their pixel matrix on the pixel matrix of the display and to generally tailor them to the characteristics of the display, recommends 1 that the “optimal viewing
22、 distance”, the “optimal horizontal viewing angle” and the “closest comfortable viewing distance” should be used as guidelines on metrics applicable to digital image systems; these are shown for various digital image systems in Table 1 and Fig. 1; 2 that Table 1 and Fig. 1 should be taken into consi
23、deration to assist administrations in identifying the digital image systems that best fit the viewing conditions of various television broadcasting applications, based on the optimal viewing distance or on the optimal horizontal viewing angle foreseen for each application; 3 that in particular, the
24、column of Table 1 entitled “Minimum display size (mm) at the closest comfortable viewing distance” should be taken into consideration as a help in identifying the maximum image resolution needed to present television images on cell-phones or hand-held receivers that have comparatively small screens
25、designed to be watched at close distance; 4 that the following Notes should be regarded as part of this Recommendation: NOTE 1 For the purpose of this Recommendation the “optimal viewing distance” of a digital image is defined as the viewing distance at which two adjacent pixels of the source image
26、(before it is re-mapped on the display) subtend an angle of 1 arc-min at the viewers eye. NOTE 2 For the purpose of this Recommendation the “optimal horizontal viewing angle” is the horizontal viewing angle under which an image is seen at its optimal viewing distance. NOTE 3 This approach was alread
27、y conceptually delineated in Recommendation ITU-R BT.1127. 2Consideration of the closest comfortable viewing distance is appropriate for real images presented on a screen. It is not appropriate for virtual images, such as those presented in holography. Rec. ITU-R BT.1845-1 3 TABLE 1 Optimal horizont
28、al viewing angle, optimal viewing distance in image heights (H) and minimum display size at the closest comfortable viewing distance (25 cm) for various digital image systems Bar in Fig. 1 Image system Reference Aspect ratio Pixel aspect ratio Optimal horizontal viewing angle Optimal viewing distanc
29、e(1)Minimum display size (mm) at the closest comfortable viewing distance(2)A 720 483 Rec. ITU-R BT.601 4:3 0.88 11 7 H 48 36 B 640 480 VGA 4:3 1 11 7 H 48 36 C 720 576 Rec. ITU-R BT.601 4:3 1.07 13 6 H 56 42 D 1 024 768 XGA 4:3 1 17 4.4 H 76 57 E 1 280 720 Rec. ITU-R BT.1543 16:9 1 21 4.8 H 93 52 F
30、 1 400 1 050 SXGA+ 4:3 1 23 3.1 H 108 81 G 1 920 1 080 Rec. ITU-R BT.709 16:9 1 32 3.1 H 144 81 H 3 840 2 160 Rec. ITU-R BT.1769 16:9 1 58 1.5 H 296 166 I 7 680 4 320 Rec. ITU-R BT.1769 16:9 1 96 0.75 H 592 333 (1)See Recommendations ITU-R BT.1127 and ITU-R BT.1769. (2)It is assumed that the screen
31、resolution capability is adequate to properly display the relevant image system. 1845-01020406080100AB CDE FGH IFIGURE 1Optimal horizontal viewing angle (degrees) for various digital image systemsNOTES: Column 2 of Table 1 gives the sampling pixel structures for the image systems denoted as A, B, et
32、c. in Table 1 and Fig. 1; column 3 gives the related reference ITU-R BT Recommendations. Rows H and I in Table 1 and the related bars in Fig. 1 identify the image systems recommended for the expanded hierarchy of large screen digital imagery (LSDI). Rows B, D and F in Table 1 and the related bars in
33、 Fig. 1 identify some image systems used in computers. Table 1 and Fig. 1 include (as examples) only some of the image rasters used in computers. For instance, the 1 366 768 image raster used in several consumer television sets is not included, since its optimal viewing distance is very close to the one indicated in row E of Table 1 for the system of Recommendation ITU-R BT.1543, which has a similar pixel count.
