1、 Rec. ITU-R BT.1702 1 RECOMMENDATION ITU-R BT.1702 Guidance for the reduction of photosensitive epileptic seizures caused by television (Question ITU-R 47/6) (2005) Scope Extensive studies on the subject of photosensitive epilepsy, which have taken place around the world, have led to formulation of
2、this Recommendation. The guidance proposed in this Recommendation is for the protection of the vulnerable section of the viewing population who have photosensitive epilepsy, and who are therefore prone to seizures triggered by flashing lights, including certain types of flashing television images. B
3、roadcasting organizations are encouraged to raise awareness among programme producers of the risks of creating television image content which may induce photosensitive epileptic seizures in susceptible viewers. Appendices 1 to 5 provide additional information on this subject. The ITU Radiocommunicat
4、ion Assembly, considering a) that several cases of individual or collective photosensitive epileptic seizures in vulnerable persons, in particular children, induced by flickering television images have been reported from various parts of the world; b) that while television images displayed on televi
5、sion receivers do not themselves cause photosensitive epilepsy, they can be a trigger of seizures in individuals who happen to be prone to photosensitive epilepsy; c) that it is useful to identify measures to help avoid the inadvertent creation of material for transmission on broadcast television th
6、at would be likely to induce photosensitive epileptic seizures; d) that measures should be proportionate to the risks and should not place undue burdens on broadcasting organizations or programme producers; e) that the impact of measures on broadcasters or programme producers may vary with their pro
7、gramme genres; f) that, to be applied effectively, such measures should be simple and easy to understand by non-technical programme producers: that in the case of some live programming, such as news, programme production is often beyond the control of the broadcaster; that measurement results to che
8、ck compliance with the guidelines depend on a number of measurement parameters; 2 Rec. ITU-R BT.1702 that the viewing environment and the display device, which can affect the likelihood of problems arising in susceptible viewers, may be different depending on a style of living around the world; g) t
9、hat the risk of seizures cannot be eliminated for the most susceptible viewers: that a small number of highly susceptible viewers may benefit from protection by means of filtering applied in the receiver; that due to the complexity of the end-to-end broadcast chain that involves many organizations a
10、nd technologies, from capture, through production, mastering, broadcast, reception to display, and considering the viewing environment, no single organization has end-to-end control over this effect, recommends 1 that broadcasting organizations should be encouraged to raise awareness among programme
11、 producers of the risks of creating television image content which may induce photosensitive epileptic seizures in susceptible viewers of television broadcasts, further recommends 1 that producers of programme material for television broadcasting, consumer equipment manufacturers, and viewers, shoul
12、d refer to the technical information provided in the Appendices; 2 that further studies are required recognizing that different programme genres exist in broadcasting environments; 3 that due to the complexity of the medical issues involved, appropriate international medical organizations (e.g. Worl
13、d Health Organization) should be consulted, and routinely informed on this issue. Appendix 1 Technical information for production organizations on flashing images in television Flickering or intermittent images and certain types of regular pattern can cause problems for some viewers who have photose
14、nsitive epilepsy. Consideration of information from leading medical opinion in this area Abramov et al., 2000; Binnie et al., 2001; Binnie et al., 2002; Clippingdale and Isono, 1999; Harding, 1998; Harding and Jeavons, 1994; Nemtsova, 2001; Wilkins, 1995 and the experience of broadcasting organizati
15、ons have led to drawing up guidelines aimed at reducing the risk of exposure to potentially harmful stimuli. Rec. ITU-R BT.1702 3 Television is by nature a flickering medium. Transmitted pictures are refreshed at typically 50 or 60 times each second, in which case interlaced scanning generates flick
16、er 25 or 30 times each second. It is therefore impossible to eliminate the risk of flashing images on television causing convulsions in viewers with photosensitive epilepsy. To reduce risk, the following guidelines on visual content should be applied when flashing or regular patterns are clearly dis
17、cernible in normal domestic viewing conditions. It should be noted that the level of any cumulative risk arising from successive sequences of “potentially harmful” flashes over a prolonged period is unknown. If, as medical opinion suggests, the risk of seizures increases with the duration of flashin
18、g, it has been calculated that a sequence of flashing images lasting more than 5 s might constitute a risk even when it complies with the guidelines below. A potentially harmful flash occurs when there is a pair of opposing changes in luminance (i.e. an increase in luminance followed by a decrease,
19、or a decrease followed by an increase) of 20 cd/m2or more(see Notes 1 and 2). This applies only when the screen luminance of the darker image is below 160 cd/m2. Irrespective of luminance, a transition to or from a saturated red is also potentially harmful. Isolated single, double, or triple flashes
20、 are acceptable, but a sequence of flashes is not permitted when both the following occur: the combined area of flashes occurring concurrently occupies more than one quarter of the displayed(see Note 3) screen area; and there are more than three flashes within any one-second period. For clarificatio
21、n, successive flashes for which the leading edges are separated by nine frames or more are acceptable in a 50 Hz environment, or separated by ten frames or more are acceptable in a 60 Hz environment, irrespective of their brightness or screen area. Rapidly changing image sequences (for example, fast
22、 cuts) are provocative if they result in areas of the screen that flash, in which case the same constraints apply as for flashes. NOTE 1 Video waveform luminance is not a direct measure of display screen brightness. Not all domestic display devices have the same gamma characteristic, but a display w
23、ith a gamma of 2.2 may be assumed for the purpose of determining electrical measurements made to check compliance with these guidelines (see Appendix 2). NOTE 2 For the purpose of measurements made to check compliance with these guidelines, pictures are assumed to be displayed in accordance with the
24、 “home viewing environment” described in Recommendation ITU-R BT.500 in which peak white corresponds to a screen illumination of 200 cd/m2. NOTE 3 It may be assumed that overscan on modern domestic television receiver displays will normally be in the range 3.5% to 1% of the overall picture width or
25、height (as indicated in European Broadcasting Union Technical Recommendation R95-2000). NOTE 4 The use of automatic video analysers to help alert production staff to potential guideline violations in video material can be beneficial. 4 Rec. ITU-R BT.1702 References ABRAMOV, V. A., KRAPIVINA E. N. an
26、d MISHENKOV, S. L. July 2000 Ecological problems of teleradiobroadcasting, Seminar of Moscow A.S. Popovs Scientific Technical Society on Broadcasting and Telecommunication, Velikie Luky. BINNIE, C. D., EMMETT J., GARDINER, P., HARDING G. F. A., HARRISON D. and WILKINS, A. J. 2001 Characterizing the
27、Flashing Television Images that Precipitate Seizures, Proc. IBC2001. BINNIE, C. D., EMMETT, J., GARDINER, P., HARDING, G. F. A., HARRISON, D. and WILKINS, A. J. July/August 2002 Characterizing the Flashing Television Images that Precipitate Seizures, SMPTE J. CLIPPINGDALE, C. and ISONO H. October 19
28、99 Photosensitivity, Broadcast Guidelines and Video Monitoring. Proc. IEEE International Conference on Systems, Man examples include photographers flashlights or strobe lights in a disco. Part of the purpose of this guidance is to assist programme producers to avoid inadvertently creating video effe
29、cts that contain flashing images or patterns likely to be harmful. Rec. ITU-R BT.1702 5 1702-0100201004060801001201401601802002003004005006007000255075100125175200225234250275300325350375400425450475500525550575600625631650675700150232861157160185200Voltage (mV)Lightoutput(cd/m2)Note 2Note 1Gamma =
30、2.2FIGURE 1Screen light output vs luminance voltageVoltage(mV)Light(cd/m2)0.10.41.22.33.85.811.214.618.620.133.539.546.153.269.378.187.697.6108.3119.5131.4143.9170.78.3Note 1 A luminance voltage of 234 mV results in light output of 20.1 cd/m2. If the brighter image ofa flash or pattern is above this
31、 level, then it is potentially harmful if the light output between the darker andbrighter images differs by 20 cd/m2or more.Note 2 A luminance voltage of 631 mV results in light output of 160 cd/m2. If the darker image of a flash or pattern is below this level, then it is potentially harmful if the
32、light output between the darker andbrighter images differs by 20 cd/m2or more.6 Rec. ITU-R BT.1702 Appendix 3 Example framework for a unified measurement specification Measurement results to check compliance with the guidelines depend on a number of measurement parameters. Since it is desirable for
33、international programme exchange that consistent measurement specification be applied uniformly worldwide, it needs further study to develop a unified specification conforming to the guidance. The flowchart in Fig. 2 illustrates an example framework for such a measurement specification. Schematics a
34、nd detailed definitions for each block will be required. It is likely that more explicit definitions and detection criteria will also be required in specifying guidance on the use of saturated red colour. 1702-02Input videosignalField/frameconversionRGBconversionGammacorrectionSpatialfilteringMotion
35、compensationMotionestimationFlickermeasurementApplythresholdsDisplayresultsIf target of processing isfields, fine horizontal stripescan give flicker indicationAppropriate block averagingreduces spurious detectionsdue to noise and fine patternsMotion compensation reducesspurious detections due topann
36、ing and object motions; ACcomponent correlation superiorAppropriate definitions ofalarm generation criteria interms of numbers of brightnesstransitions and flashing screen areaCommentsAppropriate definitions ofbrightness transition instantsFIGURE 2Example framework for a unified measurement specific
37、ationRec. ITU-R BT.1702 7 Appendix 4 Filtering techniques to reduce flashing images in television Measures to reduce the risk of the transmission of potentially harmful stimuli, as described in Appendix 1, can be expected to provide a high degree of protection for the overwhelming majority of indivi
38、duals with photosensitivity. However, for a very small number of highly susceptible individuals, measures to reduce temporal stimuli prior to transmission would place unacceptable constraints on the quality of the images broadcast, to the disbenefit of the majority of viewers. In order to make it po
39、ssible for such highly susceptible individuals to be able to watch television without significant risk of seizure, filtering techniques may be applied in the receiver. The optional inclusion of measures in receivers has the advantage of providing protection against flashing images that may from time
40、 to time arise inadvertently from a range of possible video sources. Two types of measures have been identified. Adaptive temporal filtering Adaptive temporal filtering should reduce the frame-to-frame or field-to-field stimuli in the region 10-30 Hz. The exact parameters of such filtering are left
41、to manufacturers to devise, but could typically be expected to provide a 20 dB or more reduction at temporal frequencies of 10 Hz or greater. There will be trade-offs between the effectiveness of protection, and image blur. Compound optical filters For a small number of extremely photosensitive view
42、ers, a compound optical filter may be used to effect a substantial reduction in photoparoxysmal response. Such a filter can allow highly susceptible viewers to continue to watch television or computer displays who would otherwise be unable to do so. An effective filter is likely to comprise a compou
43、nd optical filtering arrangement, one filter reflecting long-wavelength red light selectively, and the other absorbing light evenly in the visible spectrum (neutral density). 8 Rec. ITU-R BT.1702 Appendix 5 Technical information on viewing environments While the implementation of technical guidance
44、to limit potentially provocative flicker in television images is valuable in reducing the number of television-induced cases of photosensitive epilepsy, other factors in addition to programme content also affect the likelihood of problems arising: Viewing environment: a given section of programme ma
45、terial is more likely to cause problems for photosensitive viewers if viewed in a darker room; on a brighter or larger screen; or if the viewer is closer to the screen. Viewer age profile: photosensitivity is reported as most prevalent among children and young people below the age of 20 years, the p
46、revalence falling with increasing age. A combination of these factors may further exacerbate the likelihood of problems arising, and the provision of advice to viewers (and the parents of younger viewers) on appropriate viewing environments may be a valuable preventative measure in itself. Accordingly, consideration should be given on providing advice for watching television in a well-lit room from a distance of at least two metres, particularly regarding programmes aimed at younger viewers such as animations.
