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



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1 Necessity of Safety Guideline

1.1 Necessity


Unlike 2DTV, 3D TV might cause some sort of discomfort such as dizziness, headache or fatigue of eyes to some viewers. Thus it is necessary to prepare a 3DTV broadcasting safety guideline to minimize or remove the cause of such discomfort so that safer and more comfortable viewing of 3D broadcasting services is ensured.

1.2 Typical discomforts


Fatigue of eyes

• Unclear vision (eyes being dimmed)

Eyes feeling heavy

• Double vision

• Eyes being dried

Fatigue of body

• Headache or migraine

Sickness and nausea

Dizziness


2 Viewing circumstances guideline

2.1 Viewing time and rest time


Viewers are recommended to take a 5~15 min break every hour, which is also recommended for 2D video display [1].

2.2 Viewing distance


The recommend viewing distance is 3~6 times of the height of 3D video display. For example, 2~4 m is recommended for 55 inch TV. If there is not sufficient space for the above distance, viewers are recommended to view TV at the farthest distance possible.

– In case of 2D video display, viewing at too short distance deteriorates the perceivable spatial resolution, and viewing at too far distance reduces absorption. For 3D video display, another consideration is the size of binocular disparity. Viewing an image closer raises the size of binocular disparity entered into the viewer’s eyes, causing optical discomfort [2].


2.3 Viewing position

2.3.1 Viewing position


Viewers are recommended to take the position to face the centre of the video right in front of the display.

– Viewing 3D video right in front of the display minimizes distortion of scenes. Viewing the video at an oblique angle causes “shear distortion” which is a phenomenon that 3D image is distorted as if it follows the viewer. It also distorts the shape and the size of image formed on the eyes. These distortions may cause optical discomfort.


2.3.2 Horizontal viewing position


Viewers are recommended to maintain level of the display and eyes.

– Binocular disparity is given horizontally to the display. If the head of a viewer is inclined considerably to a side, the binocular disparity of the image is entered as a vertical parallax into the viewer’s stereopsis system. Therefore, the viewer feels difficulty in perceiving the depth provided by the binocular disparity. Even if the viewer manages to perceive the depth, the vertical parallax increased by the inclined head makes it difficult for the viewer to fuse two images into a single 3D image.



FIGURE 18

Horizontal viewing position


2.3.3 Right angle viewing position


Viewers should stare the display at the right angle in front of the display.

– Viewing a display with the head turned to a side makes a difference of size of image entering into eyes, causing a difficulty in fusing two images into a single 3D image.



FIGURE 19

Right angle viewing position


2.4 Others


Viewers are recommended to maintain comfortable viewing conditions by taking the following actions [1]:

Adjust light, sound and air condition of the viewing space.

– Adjust brightness and colour of the display.

3 Viewer guideline

3.1 Symptoms caused by 3D viewing on viewers


Viewers are recommended to stop viewing 3DTV if they have a headache, pain in eyes, dizziness, nausea, palpitation, unclear vision, unpleasant feeling, optical discomfort or double vision [1].

Fast movement of objects on the display or excessive accommodation-convergence mismatch/conflict may cause fatigue of eyes. In this case, viewers should stop viewing 3DTV and take a break. If viewers experience any other discomfort, they should stop watching and stare into a far distance.


3.2 Stereo blindness and stereo abnormality


Viewers with stereo blindness or stereo abnormality may suffer an optical discomfort with double vision. They are recommended to avoid watching 3D images.

– Not every person can perceive vivid stereoscopic depth from 3D images. According to the report, about 1% of population cannot perceive the stereoscopic depth for any reason, and about 30% can perceive the stereoscopic depth by detecting the stimulation for a specific depth only from the protruded or retreated images [3][4][5].

– Viewers having a strabismus or astigmatism may have a difficulty in perceiving the stereoscopic depth, and suffer more severe fatigue of eyes with double image than the viewers with normal vision.

– Amblyopia is accompanied by astigmatism in many cases for children, and mostly, they cannot perceive the stereoscopic depth. Viewers with large difference between left and right eye may have a difficulty in deceiving the stereoscopic depth.


3.3 Chronic diseases


Viewers with any chronic disease (epilepsy, cardiac disorder, high/low blood pressure, etc.) are required to pay special attention when viewing 3D images.

3.4 Age


For children under 10 it is recommended to control the viewing conditions or to give guidance on viewing 3D images, since they are in the course of development of optic system and functions, [1].

– Children have relatively shorter distance between eyes, and they perceive higher binocular disparity of 3D image than adults. Therefore, children perceive higher stereoscopic depth than adults from the same 3D image.

Ageing may deteriorate the stereopsis function.

– It is reported that ageing reduces the optical capability of deceiving the stereoscopic depth. Therefore, middle-aged/old viewers may have a difficulty in perceiving a vivid stereoscopic sense when compared to the younger age [6].


4 Content guideline

4.1 Setting stereo cameras


When producing stereoscopic image with stereo cameras, the main element is to set the parameters consistently between left and right cameras. For this purpose, the following considerations are recommended:

– It is important to adjust the optic axes of the stereo cameras. The vertical adjustment error, rotation adjustment error and intersection error must be minimized.

– The basic camera parameters must be set so that there is no error of zoom, focus, iris and colour between right/left images. It is recommended to have left and right cameras synchronized.

– Vertical inconsistency of images caused by inconsistency of optic axes is known to cause a fatigue of eyes.

– The state that the intersection point between optic axes of left and right cameras is not on the centre lines of the stereo cameras is called an intersection error. An intersection error may occur due to optic axes adjustment error even if the stereo cameras are set properly without any vertical adjustment error or rotation adjustment error. If the intersection error is excessive, the cameras cannot express the symmetric stereoscopic sense on the left/right symmetric stage, but express in appropriate stereoscopic sense.

– Excessive stereoscopic sense continued unnecessarily or sudden change of stereoscopic sense in the course of production of content may easily cause a fatigue of eyes.



FIGURE 20

Types of error of optic axis adjustment error

(A) Intersection Error



(B) Vertical Adjustment Error (C) Rotation Adjustment Error


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