Report itu-r bt. 2160-2 (10/2011)



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4.2 Taking stereoscopic images


Following considerations are recommended in taking 3D stereoscopic images.

• Images must be produced in the manner that fatigue of eyes caused by sudden change of vision should be minimized. For this purpose, images should be produced in the manner that no sudden change of disparity should occur in a short period of time, and it is recommended to prevent fatigue of eyes by adopting smooth camera work in using zoom, panning and other display techniques. It is also recommended that the images should be edited to prevent a severe change of disparity between scenes.

• 3D image distortion, which does not occur in 2D images, should be minimized. When taking images closely to an object with cross cameras, one must be careful not to make any keystone distortion. A compensating work is recommended if the eyes are not comfortable with the images.

• In taking images, one should be careful in using zoom lenses, and it is recommended to minimize the cardboard effect and the puppet theatre effect by adjusting the space between cameras.

• When presenting an object near a side edge of the display, the object should not be projected if possible.

• If the depth of an object perceived through binocular screen disparity is too small when compared to the known depth of the object, a cardboard effect may occur. In this case, this effect should be minimized with the camera work [8].

• A puppet theatre effect is made when there is a gap between the stereoscopic image displayed and the size of the object perceived in the real world. Viewers are likely to perceive an object as small as a doll. This effect easily occurs especially on a small display [8].

• A disparity between left and right images should be consistent if the image is produced properly. If a scene is taken with cross stereo cameras, the image produces a keystone distortion in the echelon formation with inappropriate vertical parallax. The vertical parallax increases as the space between cross stereo cameras grows and the focal distance of the lens reduces [9].

• Cross stereo cameras may create an inappropriate horizontal parallax, which in turn, causes a distortion of stereoscopic depth. Viewers may perceive that an object at the edge is farther than that in the centre of the display [9].

4.3 Caption


In 3DTV, the caption must be displayed in front of objects in order to prevent that the caption is unnaturally inside an object. If an object is projected, however, the caption being nearer to viewers than the object may cause a fatigue of eyes due to an excessive disparity. In this case, it is recommended to change the position of the caption to prevent fatigue of eyes.

4.4 Screen disparity


• For uncrossed disparity, the screen disparity between left/right images should not exceed the average gap between eyes.

• For crossed disparity, excessive screen disparity between left/right images may cause a fatigue of eyes.

• Continued viewing of excessive binocular disparity causes a fatigue of eyes. Therefore, it is recommended not to present excessive crossed disparity continuously.

5 Display guideline

5.1 Crosstalk of display


A crosstalk of display causes discomfort in viewing stereoscopic images. It is recommended to minimize crosstalk in consideration of the following:

– A crosstalk of display is a phenomenon occurring due to incomplete separation of left and right images. It varies depending on the display method and left/right image separation method. For example, in the polariscopic method, crosstalk is caused by the optical performance of the polarizing filter and the incomplete adjustment between the polarizing filter and the display pixel elements. In case of active shutter method, the pixel response speed becomes the main factor of crosstalk.

– Crosstalk of display is an independent parameter to the content, and can be indicated in an objective value for each display. For example, the crosstalk for the left eye is induced from the brightness of the right image versus that of the left image seen by the left eye, and vice versa.

The crosstalk experienced subjectively by viewers may be caused by the content, as well as the display crosstalk. Therefore, it is recommended to consider the following when producing a content:

– Subjective crosstalk experienced increases if there is a large contrast or binocular disparity between left and right images at the same position of the display [7].

5.2 Display refresh rate


In order to prevent flickering, the refresh rate of left and right images should be 60 Hz or higher. Therefore, the total refresh rate of a time-division 3D display should be 120 Hz or higher.

5.3 3D glasses


In addition to the display crosstalk, crosstalk may occur due to the glasses. Therefore, it is recommended to consider the following to minimize crosstalk:

– For polarized glasses, leakage of light caused by optical performance of the polarizing filter generates crosstalk. For active shutter glasses, crosstalk is generated by the light penetrated due to the optical performance of the glasses when the liquid crystal is closed, and the sync timing gap between the display and the glasses.

– Active shutter glasses acquire information on synchronization between left and right images and the action commands are acquired via communication with the display. In order to acquire an intensive image effect with 3D glasses at conversion from 2D to 3D and during viewing 3D images, the signals and protocols for communication shall be robust against external interference, and interruption shall be minimized.

References

[1] ISO IWA3, Image safety-Reducing the incidence of undesirable biomedical effects caused by visual image sequences, 2005

[2] Sugawara, M., Mitiani, K., Kanazawa, F.M., Okano, F. & Nishida, Y., “Future prospects of HDTV – Technical trends toward 1080p”, Paper presented IBC2005 conference, 2005

[3] van Ee, R., “Correlation between stereoanomaly and perceived depth when disparity and motion interact in binocular matching”, Perception, 32, pp.67-84, 2003

[4] Richards, W., “Stereopsis and stereoblindness. Experimental Brain Research”, 10, pp. 380-388, 1970

[5] Richards, W., “Anomalous stereoscopic depth perception”, Journal of the Optical Society of America, 61, pp.410-419, 1971

[6] Bell, B., Wolf, E., & Bernholz, C. D., “Depth perception as a function of age”, Aging and Human Development, 3, pp.77-81, 1972

[7] Woods, A.J., “Understanding crosstalk in stereoscopic displays”, Keynote presentation in 3DSA conference, Tokyo, Japan, pp.19-21, 2010

[8] Lydia M.J. Meetsters, Wijnand A. IJsselsteijn, and Pieter J.H. Seuntiens, “A Survey of Perceptual Evaluations and Requirements of Three-Dimensional TV”, IEEE Transactions on circuits and systems for video technology, vol. 14, no. 3, pp.381-391, 2004

[9] Andrew Woods, “Image Distortions in Stereoscopic Video Systems”, Stereoscopic Displays and Applications IV, Proceedings of the SPIE Vol. 1915, San Jose, CA, 1993



Annex 6

Italian Health Ministry Circular Letters

The Italian Health Ministry issued a Circular Letter dated March 17, 2010, addressed to all the Regional Health Agencies, the Police, the associations of cinema operators and for information to the Ministry for Economy Development, which is responsible for telecommunications including broadcasting. The Italian Ministry action was prompted by a request of the Italian Consumer Protection Authority, and it was based on advice provided by the Ministry’s High Advisory Council on Health. Some further clarifications were issued in a subsequent circular letter dated 6 August 2010.

The circulars are available (in Italian) on the website of the Ministry, and a translation is provided below.

The Ministry circular letter of March 17, 2010 states that:

– the scientific literature does not seem to provide firm proof that viewing stereoscopic programming would force human eyes and brain to perform unnatural processing of visual information; consequently there are no clinical indications at this moment against the use of 3D spectacles during cinema screenings, on condition that such screenings are limited in duration (the advice of the High Advisory Council on Health on this point was more detailed: it is suggested that viewing should be limited in time, and that it should contain intermissions proportionate to the total programme duration);

– some functional problems may arise in young viewers due to the use of 3D spectacles to view cinema presentations, because binocular vision may not yet be present or well established in young viewers, or because they may be cross-eyed or amblyopic, or because they may be going through a period of visus rehabilitation; however those problems should cause no irreversible damage or pathologies;

– consequently, the public that attends stereoscopic screenings should be informed that children under six years should not use 3D spectacles and that even adults should not use them for a duration that exceeds a single screening session.

A further circular letter of the Ministry, dated 6 August 2010, stated that in those cases when single-use glasses cannot be considered due to their technology or cost, 3D glasses must be properly disinfected and repackaged before they are provided to the next user since the risk of transmission of bacterial infections tends to increase with the successive use of the same spectacles by different viewers.

Annex 7

Example notifications given to viewers in Japan


Background


The following notifications prepared by DPA16 are presented to viewers on the air before stereoscopic 3DTV programmes are broadcast or by the web site.

1 Notifications when 3D programmes are broadcast on same channel as 2D programmes


• This programme is 3DTV. (When a 3DTV programme starts.)

• The 3DTV programme is about to end, and will be followed by a 2DTV programme. (When a 3DTV programme ends.)

• Change the “3D/2D” mode as appropriate. (When the type of programme, i.e. 3D or 2D, changes.)

2 Notifications that should be broadcast with 3DTV programmes


• Watch TV in a well-lighted room and at an adequate viewing distance.

• Stop watching, take off your 3D glasses, and take a rest if feeling discomfort while watching 3DTV.

• Supervise infants’ viewing of 3DTV.

• Check whether stereoscopic images can be correctly seen or not by using inserted clips before starting 3DTV programmes.


3 Notifications may inform viewers, even though some of these are basically in the product manual


• Prepare appropriate products for 3DTV to use in programmes.

• Side-by-side images may be shown on the display when watching 3DTV programmes on 2D television.

• The On Screen Display (OSD) may disrupt 3D images.

• Refer to safety precautions in using 3D eyewear.



• Information on content of 3DTV programmes is available from the electronic programme guide (EPG) or homepage to help with programme choices. `
Annex 8





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