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REPORT ITU-R BT.2293-0
Principles for the comfortable viewing of stereoscopic
three-dimensional television (3DTV) images
With the increasing interest in stereoscopic three-dimensional (3D) content services, concerns have been raised about the comfort and safety of viewing stereoscopic images. These concerns have been recognized as part of the bottleneck preventing the proliferation of stereoscopic 3DTV content services into the mass market. As a result, it has become important that adequate information and guidance is available to producers of stereoscopic 3DTV content in order to assist with the production of programmes that are comfortable to watch. The aim of this Report is to collate the available information and to highlight some of the concerns that have been expressed about viewing 3D images, especially to younger viewers1.
3D viewing safety is of primary importance for the popularization of 3D content. In the 1950s, stereoscopic content won commercial success in Hollywood for a short time. However, strong headaches and visual discomfort caused by excessive binocular disparity and the crudeness of the production equipment were reported, and the market literally died until the early 21st century. Visual discomfort was one of the primary reasons cited for the loss of interest in stereoscopic images. Therefore, safety guidelines for the production, distribution and viewing of 3DTV programmes are vital to the success of commercializing 3DTV broadcasting especially if producers expect to achieve long hours of continuous viewing.
Now that 3DTV services are available in the home, the home viewing environment has become a critical factor to be taken into account when assessing how comfortable a stereoscopic 3DTV programme is to watch. Very few broadcasters or administrations however, make information available to help viewers get the best experience from these services.
TABLE OF CONTENTS
1 Principles for comfortable viewing of stereoscopic three-dimensional images 6
1.1 Composite factors in perception of stereoscopic 3D images 6
1.2 Measures to enable comfortable viewing of stereoscopic three-dimensional images 6
2 Psychophysical aspects of viewing stereoscopic images 7
2.1 Psychophysical aspects 7
2.2 Visual discomfort induced by disparity and motion magnitude of stereoscopic video 10
2.3 The influence of stereopsis and abnormal binocular vision on ocular and systemic discomfort while watching 3D television 10
2.4 The impact of Parkinson’s Disease on discomfort while watching 3D television 10
2.5 Influence of Alzheimer’s Dementia on dynamic 3D perception and fatigue 11
2.6 3D viewing and refractive errors in children 11
3 Points to consider for broadcasters to provide comfortable 3DTV broadcasting 12
3.1 Preparation 12
3.2 Shooting (acquisition) and editing 12
3.3 Verification 13
3.4 Broadcasting 13
4 Conclusions 13
4.1 Guidance to viewers of 3DTV services 13
Annex 1 – Example notifications given to viewers in Japan 15
1 Notifications when 3D programmes are broadcast on same channel as 2D programmes 15
2 Notifications that should be broadcast with 3DTV programmes 15
3 Notifications may inform viewers (even though some of these are basically in the product manual) 15
Annex 2 – Examples of safety guidelines – Korea (Republic of) 16
1 The necessity for safety guidelines 16
1.1 Background 16
1.2 Typical discomforts 16
2 Viewing guidelines 16
2.1 Viewing time and rest time 16
2.2 Viewing distance 17
2.3 Viewing position 17
2.4 Others criteria 18
3 Viewer guidelines 18
3.1 Symptoms caused by 3D viewing on viewers 18
3.2 Stereo blindness and stereo abnormality 18
3.3 Chronic diseases 18
3.4 Age 19
4 Content guideline 19
4.1 Setting stereo cameras 19
4.2 Capturing stereoscopic images 20
4.3 Captions and Graphics 21
4.4 Screen disparity 21
5 Display guidelines 21
5.1 Crosstalk in the display 21
5.2 Display refresh rate 22
5.3 3D glasses 22
Annex 3 – Examples of safety guidelines Italian Health Ministry Circular Letters 23
Annex 4 – Psychophysical studies on three dimensional television systems 24
1 Key items for psychophysical studies 24
1.1 Naturalness and unnaturalness of images 24
1.2 Viewing comfort and discomfort 24
1.3 Visual fatigue caused by parallax 3DTV viewing 25
1.4 Individual differences in the stereopsis function 25
1.5 Effect on young people 25
2 Naturalness and unnaturalness of stereoscopic images − Geometrical analysis of spaces reproduced by stereoscopic images 26
2.1 Theoretical analysis of reproduced spaces 26
2.2 Size distortion 29
2.3 Depth distortion 32
3 Viewing comfort and discomfort of stereoscopic images 35
3.1 Parallax distribution and visual comfort of stereoscopic images 35
3.2 Visual comfort and discomfort in viewing stereoscopic images 39
4 Visual fatigue in viewing stereoscopic images 41
4.1 Experimental results on inconsistency between vergence and accommodation 41
4.2 Experimental results on parallax amount and lateral/depth motion 42
4.3 Evaluation of fatigue caused by watching 3DTV 44
5 Spatial distortion prediction system for 3DTV 46
5.1 Introduction 46
5.2 Spatial distortion in 3DTV 46
5.3 Spatial distortion prediction system for 3DTV 46
Annex 5 – Results of subjective visual comfort assessment for motion and disparity magnitude of 3D content – Korea (Republic of) 50
1 Summary and proposals 50
2 Experimental environments 50
3 Subjective measurement of visual discomfort induced by motion characteristics 51
3.1 Visual stimulus 51
3.2 Subjective assessment method of visual comfort 52
3.3 Experimental results and discussion 54
4 Subjective measurement of visual discomfort induced by depth characteristics 57
4.1 Visual stimulus 57
4.2 Subjective visual comfort assessment method 58
4.3 Experimental results and discussion 58
Annex 6 – The influence of stereopsis and abnormal binocular vision on ocular and systemic discomfort while watching 3D television – Korea (Republic of) 60
1 Summary and proposals 60
2 Abstract 60
3 Participants and methods 61
4 Results 62
5 Discussion 62
Annex 7 – The influences of Parkinson’s diseases on dynamic 3D perception and fatigue while watching 3D television – Korea (Republic of) 64
1 Introduction and study results 64
2 Summary and proposals 65
Attachment – Subjects and methods 65
Annex 8 – Visual discomfort induced by the binocular disparity of stereoscopic video – Korea (Republic of) 67
1 Introduction and study results 67
2 Summary and proposals 67
Attachment – Results of subjective visual comfort assessment for disparity and motion depth magnitude of 3D content 68
1 Experimental environments 68
2 Subjective measurement of visual discomfort induced by disparity characteristics 68
2.1 Visual stimulus 68
2.2 Subjective assessment method of visual discomfort 72
2.3 Experimental results and discussion 74
Annex 9 – Liaison statement to the WHO 78
Annex 10 – The Influence of Alzheimer’s Dementia on dynamic 3D perception and fatigue while watching 3D Televison 79
Annex 11 – The role of 3D Television in terms of refractive errors in children 82
1 Normal subjects 83
2 Subjects with exodeviation 84
1 Principles for comfortable viewing of stereoscopic three-dimensional images
1.1 Composite factors in perception of stereoscopic 3D images
A stereoscopic 3D system expresses depth by presenting video that has disparity2 with respect to the left and right eyes of the viewer. The perception of depth depends on factors such as the programme production techniques, the display devices, the 3D glasses (if required), the viewing conditions, and the viewer’s physical characteristics. Any visual fatigue associated with the viewing of stereoscopic 3DTV programmes will be, to a greater or lesser extent, dependent on these as well as other factors such as spatial distortion.
NOTE – Section 5 of Annex 4 describes a spatial distortion prediction system for 3DTV that calculates the spatial distortion of a reproduced stereoscopic image and predicts the extent of the puppet-theatre and cardboard effects, excessive binocular parallax, and excessive parallax distribution.
1.2 Measures to enable comfortable viewing of stereoscopic three-dimensional images
The complexity of the end-to-end broadcast chain, which now involves many different organizations, processes and technologies (from capture, through post-production, mastering, broadcast, reception and display) means no single organization can exercise an overall control of end-to-end quality of a programme.
All parties concerned with stereoscopic 3DTV systems should take the characteristics of stereoscopic 3D systems, described in § 1.1, into account when manufacturing equipment, producing programmes and displaying 3D images and pay particular attention to how the programmes may be viewed by the intended audience. It is not reasonable to expect that solely regulating the amount of parallax in 3DTV programmes is enough to ensure viewer comfort.
1.2.1 Programme production
It is important to identify measures to help avoid the inadvertent creation of material for transmission on broadcast television that could induce visual fatigue and other possible health hazards.
Measures should be proportionate to the risks and should not place undue burdens on broadcasting organizations or programme producers. The impact of measures on broadcasters or programme producers may vary with their programme genres and the intended target age range of the audience.
On occasions, programme production is beyond the control of the broadcaster especially during live broadcasts such as sport or music concerts; therefore broadcasting organizations should be encouraged to raise awareness among programme producers of the risks of creating stereoscopic television images that may induce visual fatigue.
This awareness could range from simple information pamphlets and on-line training through to detailed instruction and practical (hands on) training courses.
Training should be designed to give producers of 3DTV programmes the understanding of the characteristics of stereoscopic 3D images and the impact to the viewer of 3D video techniques.
1.2.2 Viewing environments and display devices
It must be recognized that home viewing environments and display devices have an impact on the likelihood of visual problems and that these viewing conditions will differ between households, reflecting the style of living. It is therefore important that viewers are also well informed of requirements for satisfactory viewing of stereoscopic 3D images.
1.2.3 Examples of safety guidelines
In 2010, a liaison statement (see Annex 9) was sent to the WHO requesting information on potential impact on health of 3D. In their reply, they stated that they could not give any direct information from their own files, as they presently do not have a project on this topic.
Some administrations have therefore issued their own guidance. For examples of such guidance given by some national bodies see:
Annex 1: Example of safety guidelines – Japan
Annex 2: Examples of safety guidelines – Korea (Republic of)
Annex 3: Examples of safety guidelines – Italian Health Ministry
2.1 Psychophysical aspects
It is necessary to gain a full understanding of the results of psychophysical studies before attempting to implement new broadcast schemes, in order to fully understand the effects to which the viewer is subjected and the performance that is required of the main equipment in these systems. There are a number of issues to be studied before the effects of viewing three-dimensional images on human perception and visual functions can be fully understood.
Section 1 of Annex 4 “Psychophysical studies on three dimensional television systems” identifies some key study items on the psychophysical aspects of stereoscopic television systems. It also includes the results of studies related to the naturalness and unnaturalness of stereoscopic video, the evaluation of visual comfort based on an analysis of parallax distributions within certain frames, and the visual fatigue by viewing stereoscopic video.
A major disadvantage of current implementations of stereoscopic television is the presentation of the stereoscopic images on a single surface (the display screen). There is evidence that this can give rise to a potential conflict between “vergence” (the eye movement to target both eyes to the same point on the screen) and “accommodation” (the action by which the “lens” in the viewer’s eye focuses on that point). It has been documented in medical literature that this conflict can cause viewer’s discomfort, eye fatigue, headache and possibly other health hazards notably if the viewing continues for an extended period of time3, 4.
Such effects have been noticed in some trial broadcasts. For example, one of the terrestrial broadcasters in the Republic of Korea, SBS (Seoul Broadcasting System), broadcast South Africa World Cup Soccer Games in 3D from 11th June 2010. In a survey of nearly 100 viewers, 75% expressed satisfaction with the trial 3DTV broadcasting service. However, the survey showed that 30% of the viewer felt dizziness, double image and eye fatigue.
Factors that affect 3D viewing comfort also include inter-pupillary distance, intra-scene disparity range, and the speed of depth change of objects in the scene. In addition, rapid cuts between shots of differing depths and changing depths with zoom or pans are known to cause viewer discomfort. Some of these techniques are commonly used to make 2D production more engaging but when applied to 3D programmes, might cause discomfort to the 3D viewer. Similarly, applying 3D production techniques tends to create a 2D programme that might be considered by 2D viewers as boring. It is for this reason that many 3D productions to date have been different from the 2D productions of the same event or release. It is widely known that current 3D movie releases are editorially different from the 2D releases.
Parallax is affected by the programme production technique, display device, viewing conditions, and viewer characteristics (such as inter-pupil distance). Accordingly, all parties concerned with stereoscopic 3D systems should take this characteristic of stereoscopic 3D systems into account.
2.1.1 Geometrical relationships and naturalness
The reproduction of depth information is essential for people to gain a realistic sense of three‑dimensionality from a stereoscopic image. Depth distortion in the stereoscopic image can create an unnatural impression when the image is viewed.
In stereoscopic imaging, the object is imaged using two cameras. The arrangement of these two cameras can be classified into;
• parallel configurations, where the optical axes of the two cameras are parallel with each other, and
• intersecting “toed-in” configurations where the two optical axes are made to intersect.
A parallel configuration will produce a stereoscopic image with no spatial distortion when the gap between the centre of each camera lens is set equal to the gap between the pupils, the horizontal offset of the left and right images projected on the screen is equal to the gap between the pupils, and the camera’s angle of view is equal to the expected viewing angle of the display. In such cases, the image is said to be viewed under orthostereoscopic (distortion-free) conditions. However when actual programme production and viewing conditions are taken into consideration, it is difficult to ensure that distortion-free conditions are always satisfied. If these conditions are not met the spatial distortion of the stereoscopic image can cause unnatural effects such as the “puppet theatre” effect where the stereoscopic images of foreground objects appear unnaturally small, and the “cardboard” effect, where the stereoscopic image of an object appears unnaturally thin.
Section 2 of Annex 4 presents a geometric analysis of reproduced stereoscopic image spaces and discusses the results and their relationship to the distortion of reproduced stereoscopic image spaces. The results of subjective evaluation tests that support these findings are also shown. The discussion relates to how the reproduced stereoscopic image space is affected by parameters such as the camera configuration (parallel or toed-in), display screen size, and viewing distance.
2.1.2 Visual comfort and discomfort in viewing stereoscopic images
Finding a way to make the visual comfort of stereoscopic images a measurable physical factor is arguably one of the key issues in stereoscopic imaging research. As has been stated, stereoscopic images convey depth information to the viewer by making use of the parallax between the images presented to the left and right eyes. If we could ascertain how the magnitude and distribution characteristics of this parallax relate to the visual comfort of the image, this information would be very useful for the production of stereoscopic images.
How these parameters relate to the subjective visual comfort was studied by focusing on the average and range of the parallax distributions. It was shown that they both have a correlation with the visual comfort of stereoscopic images and that the range of parallax distributions in stereoscopic images appraised as visually comfortable was almost 60 pixels in HDTV image. It was also suggested that stereoscopic images tend to become more visually comfortable when the average value of the parallax distribution approaches zero (i.e. at apparent positions closer to the display screen).
In a stereo 3D system the presentation of two images to the respective left and right eyes forms a binocular 3D image. If discrepancies arise between these images due to the systems used for production, storage, transmission or display, they can cause psychophysical stress, and in some cases 3D viewing can fail. For example, when shooting and displaying stereoscopic 3DTV programmes, there can be geometrical distortions, such as size inconsistency, vertical shift, and rotation error, between left and right images. It is important that such geometrical distortions should be suppressed. Similarly stereoscopic image cross-talk, where the images “leak” and can be partially seen by the opposite eye, can also result in discomfort for the viewer and equipment, especially display equipment (including 3D glasses) should be designed to minimize this effect. Detection and tolerance limits of evaluating visual discomfort in terms of cross-talk were reported to be highly dependent on image content and display contrast, and cross talk must be reduced on high contrast displays.
Section 3 of Annex 4 presents some results of subjective evaluation tests with regard to visual comfort in viewing stereoscopic images. The results indicate that stereoscopic image having an excessive range of parallax distribution can be evaluated as uncomfortable to view. The research results on visual discomfort caused by discrepancies between left and right images are also shown. The results indicate the detection and tolerance limit of discrepancies with regard to visual discomfort in viewing stereoscopic images.
2.1.3 Visual fatigue in viewing stereoscopic images
Two of the major factors that cause visual fatigue are:
• The difficulty in fusing left and right retinal images with large binocular parallax. This demands an increased viewer fusion effort. Fusion effort is based on two factors: the principle of stereoscopic image display (defined by horizontal binocular parallax, inevitable in stereoscopic systems), and issues emanating from the display hardware itself (leading to differences between views of left and right images).
• A dissociation of vergence and accommodation due to the difference in visual functions between viewing real objects and viewing stereoscopic images. The vergence point is positioned within the depth of field when viewing a real object. On the other hand, the vergence point is sometimes outside the depth of field when binocular parallax is large in viewing stereoscopic images. Temporal discontinuous changes in dissociation can also lead to visual fatigue.
2.1.4 Assessment methodology
It is understood that traditional testing methodologies such as PSNR, might not be indicative of the effect of artefacts, and that new metrics will need to be considered. Development of appropriate assessment methodology, in conjunction with a common set of reference source material is therefore of the utmost importance for evaluating 3DTV systems.
The ITU details a method for the subjective assessment of image quality and depth quality in Recommendation ITU‑R BT.1438 – Subjective assessment of stereoscopic television pictures.
Recommendation ITU-R BT.2021 – Subjective methods for the assessment of stereoscopic 3DTV systems, details the recommended methodology for the assessment of 3D image quality.
Recommendation ITU-R BT.2021 Annex 1 details sets of criteria that should be considered when assessing visual comfort;
“Primary perceptual dimensions” are “visual comfort”, “picture quality” and depth quality”.
“Additional perceptual dimensions” are “sense of presence”, sensation of reality and “naturalness”.
It is important that these criteria are used to assess the impact on the comfort of viewing 3DTV programmes through the entire broadcast process including the effects of bandwidth reduction used for contribution and eventual distribution of stereoscopic programmes. Allowances should also be made for the duration of a stereoscopic programme (the length of time a viewer will be watching in 3D), as production techniques that are acceptable for short programmes might cause discomfort if applied over a long period of time
2.2 Visual discomfort induced by disparity and motion magnitude of stereoscopic video
It has been known that the motion and depth characteristics of 3D content are central determinants of visual discomfort during stereoscopic 3DTV viewing. In order to investigate the influence of these motion and depth characteristics on visual comfort, subjective visual comfort assessments were conducted using visual stimuli with various disparities, motion velocities, and motion directions. In addition, subjects were given a questionnaire in order to investigate some of the physical symptoms accompanied by the perceived visual discomfort.
The experimental results showed that an increase in velocity of horizontal, vertical, and depth motion induced more visual discomfort. A questionnaire accompanying the test reveals that the subjects felt focusing difficulties due to fast spatial and temporal changes of disparity in stereoscopic 3D content. In addition, subjects reported a higher degree of visual discomfort as the binocular disparity increased. Overall symptoms of visual discomfort can become severe and are often encountered as focusing difficulty and eyestrain. The results of subjective visual comfort assessments for motion and disparity magnitude of 3D content are given in Annex 5.
2.3 The influence of stereopsis and abnormal binocular vision on ocular and systemic discomfort while watching 3D television
Stereopsis refers to an awareness of the distances of objects from the observer and binocular vision is necessary to perceive stereopsis. The term stereopsis is often used synonymously with binocular depth perception. Image processing is essential to the perception of stereopsis and many components of stereopsis such as retina disparity, eye movement, primary perception of brain and image processing functions are important therefore people with abnormal binocular vision (ABV), including strabismus, amblyopia, and anisometropia, may vary in their ability to perceive 3D images according to their degree of stereopsis.
In a study carried out by the Republic of Korea (see Annex 6 for full details), 98 people with ABV and 32 normal binocular vision subjects were enrolled to evaluate the degree of 3D perception and ocular and systemic discomfort (3D fatigue) in people with ABV and their relationship to stereo acuity while watching a 3D television.
2.3.2 Methodology and results
Best corrected visual acuity, refractive errors, angle of strabismus, and stereopsis were measured. After watching 3D television for 20 minutes, a survey was given to each subject to evaluate the degree of 3D perception and 3D fatigue while watching 3DTV. The participants with ABV showed a lower degree of 3D perception. However, the amount of 3D fatigue did not differ from normal participants. According to the degree of stereopsis, the study compared the subjects of normal stereo acuity with those of abnormal stereo acuity. Subjects with normal stereo acuity reported more 3D fatigue, although they perceived 3D better. People with ABV who had a high degree of stereopsis felt more 3D fatigue than normal participants. Those with exotropia reported 3D fatigue most frequently.
Section 4 of Annex 6 presents some experimental results of subjective evaluation with regard to visual fatigue in viewing stereoscopic images. The results indicate that inconsistencies between vergence and accommodation can cause visual fatigue.
2.4 The impact of Parkinson’s Disease on discomfort while watching 3D television
People with Parkinson’s disease often experience the degeneration of dopamine-generating cells in the brain, have retina problems, eyeball movement problems and visual perception problems. Dopamine is a chemical messenger for light adaptation, and it controls the flow of information through cone circuits and rod circuits in the retina, Parkinson’s disease sufferers are known to perceive visual stimuli poorly.
A study carried out in the Republic of Korea concluded there was no significant difference in dynamic 3D perception between those with Parkinson’s disease to a control group. The study also concluded there was no difference in 3D fatigue between the two groups.
Further details of research can be found in Annex 7.
2.5 Influence of Alzheimer’s Dementia on dynamic 3D perception and fatigue5
As has been said, image processing is essential to the perception of stereopsis. This information processing system is used to watch 3DTV and some people with dementia may have problems perceiving a 3DTV image.
A further study carried out in the Republic of Korea, conducted with people suffering from Alzheimer’s dementia has shown that 3D perception is significantly lower. In terms of safety, the components of 3D discomfort did not differ between the control group and those with Alzheimer’s dementia.
Further details on this research can be found in Annex 10.
2.6 3D viewing and refractive errors in children
Due to its high prevalence, reported up to 96.5% in Asia, myopia is a major public health problem. Close up working or “near-work”, is a well-established environmental factor related to the development and progression of myopia. Near-working induces accommodation, and after prolonged accommodation, transient myopic shifts can be observed even after the work has ceased. This near-work induced myopia can be considered a possible environmental myopigenic factor.
Watching 3D video requires more accommodation than watching 2D video. If unnecessary accommodation induces more transient myopic shift, it might lead to the development and progression of permanent myopia.
To assess the role of 3DTV in terms of refractive errors in children the following questions need to he answered:
1) Are there any refractive changes such as a transient myopic shift after watching 3DTV?
2) Do myopes or exotropes show more myopic shift?
3) Do changing refractive errors persist after 10 minutes of rest in subjects who showed myopic shift?
In order to fully understand these issues, a study carried out in the Republic of Korea found the following.
Watching properly made 3D content on a 3DTV for 50 minutes at 2.8 metres did not influence the refractive errors of myopic or exotropic subjects more than for other subjects nor did it lead to refractive errors in children.
The mean refractive error of subjects with myopic shift returned to a baseline value after 10 minutes of rest without producing any residual near-work induced myopia.
To prevent myopic shifts after watching 3DTV, the following factors were controlled:
• Allowing for properly produced 3D content (image disparity within ±1 degree).
• A watching duration of less than 50 minutes.
• A viewing distance of more than 2.8 metres.
• 10 minutes of rest after 50 minutes of watching.
These observations should be considered when developing viewing safety guidelines.
A full report of the study can be found in Annex 11.
3 Points to consider for broadcasters to provide comfortable 3DTV broadcasting
Positive disparity, negative disparity, depth budget, and depth motion cause inconsistency of accommodation and vergence in the creation of stereoscopic 3D content. They also differ in terms of binocular disparity, which is the positional difference of two images delivered to human eyes, and therefore the visual fatigue caused by binocular disparity while watching 3D images requires a study in terms of content. Annex 8 gives further detail of visual discomfort induced by the binocular disparity of stereoscopic video and guidance to minimize such discomfort.
Broadcasters who are commissioning and distributing 3D programmes should be able to give advice to those producing the 3D programmes on techniques that should ensure they can be comfortably viewed. This advice includes (but is not limited too) the following areas.
Because 3D images based on binocular disparity have a risk of causing discomfort to viewers if conventional 2D production techniques are used, it is important that all staff involved with 3D production should fully understand the characteristics of the 3D image technology.
It is advisable to continual update the training to the staff engaged in the production on the fundamentals of 3D image technology, psychophysical effects of 3D images, and characteristics and operations of 3D cameras and other related devices, by referring to the latest information from case examples and academic publications.
3.2 Shooting (acquisition) and editing
Currently, it is preferable to assign a stereographer (a specialist in 3D production) to every 3DTV programme.
The stereographer should oversee the 3D image space design in advance of the production and select the most appropriate equipment for the subject to provide a proper sense of depth.
The stereographer should establish the target screen size(s) for the programme during the early planning stages. This information will allow a reasonable depth budget to be set for target audience’s viewing environment and help to minimize the risk of viewer discomfort.
When shooting a concert or a sports event, where several cameras are arranged and switched in real time, equipment suitable for camera angle and shooting distance needs to be selected.
Equipment capable of controlling the shifts and parallax between the right and left images in real time should be used with cameras used for wide panning shots and zooms. Where possible a “3D‑puller” (a new job roll within a 3D vision team) should be assigned for each camera pair to control the depth so that a 3D image space will not be broken up.
Where such real time control is not practical, a range of shooting conditions for comfort should be verified in advance and the shifts and parallax between the left and right images should be adjusted post-production.
For a live 3DTV broadcast, the stereographer should work with the camera operators, 3D-pullers and other staff to ensure that 3D images can be viewed comfortably.
For non-real-time broadcasting of edited programmes, it is preferable that the stereographer used during the shooting supervises the post-production of the 3D images and is in attendance at any depth grade (where the various parameters controlling the 3D look are balanced and adjusted – this is analogous to a colour grading session). It is also preferable that when time permits the programme is previewed by several staff who have not been involved in the post-production process.
A subjective assessment test with non‑expert observers may also be conducted as necessary. Where defects are found by during the preview or subjective testing, the shots or sequences affected should be adjusted or re-edited.
When broadcasting 3D images, it is preferable to advise viewers on how to view 3DTV comfortably in terms of psychophysical effects and safety issues.
The importance of giving careful consideration to each stage of the production and broadcasting of 3DTV programmes to ensure the viewer does not experience discomfort cannot be underestimated.
Recommendation ITU-R BT. clearly states the key points to consider when evaluating 3DTV image quality and as such offers programme makers guidance on what to look out for during production if they wish to make the programme comfortable to watch. These points also offer guidance to those whose role it is to review the quality of the finished product.
4.1 Guidance to viewers of 3DTV services
As has been stated, the home viewing environment has become a critical factor that has to be taken into account when assessing how comfortable a stereoscopic 3D programme is to watch but there is very little advice available to viewers about how to get the best from the 3D services.
Below is an example of guidance that could form part of any information made available to viewers of 3DTV services:
Watching 3DTV programmes in your home
To get the best experience from watching 3D programmes at home it is important to make sure the viewing environment is set up properly. This will reduce any risk of eyestrain or feeling uncomfortable whilst viewing.
The following are some simple guidelines that will make sure you get the best viewing experience:
• 3D will look its best if it is viewed in a room with good ambient lighting.
• Many 3D televisions give a better 3D effect if you are seated directly in front of the screen (not to either side).
• Sit a reasonable distance from the screen – between three and six times the height of the screen usually gives the best experience.
• Make sure both lenses of the 3D glasses are clean and that “active” glasses have adequate charge in their batteries (see the manufactures instructions for your 3DTV).
• Stop watching and take off the 3D glasses if you feel any discomfort.
• Children should be supervised when watching 3D programmes and they should not watch 3DTV for long periods.
Some people have problems with depth perception and there are other medical conditions that can affect a person’s ability comfortably watch 3DTV programmes. If you or a member of your family has a strong reaction while watching 3DTV, it would be advisable to consult an optician or other qualified practitioner as soon as practical.
Example notifications given to viewers in Japan
The following notifications prepared by DPA6, are presented to viewers before a stereoscopic 3DTV programme is broadcast either “on-screen’ or by directing viewers to a website.
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.
Examples of safety guidelines – Korea (Republic of)
A 3DTV Project Group (PG806) has been established in Korea with the aim of developing a 3DTV broadcasting specification and viewing safety guideline. Working group WG8062 is focusing on the development of a 3DTV viewing safety guideline for displays, content, viewing conditions, and viewer parameters.
The Telecommunications Technology Association of Korea (TTA) published “3DTV Broadcasting Safety Guideline” in December 2010. Its purpose is to give advice on how to reduce visual fatigue and the most suitable viewing conditions for the safe viewing of stereoscopic content. This advice is also intended to assist the 3D industries (programme makers and equipment manufacturers) reduce any potential risks from the viewing stereoscopic content.
The guideline will be updated as new information from clinical research into the viewing of 3DTV becomes available.
See also Annex 5 for details of the results of subjective visual comfort assessment for motion and disparity magnitude of 3D content carried out by the Republic of Korea.
1 The necessity for safety guidelines
Unlike 2DTV, 3DTV might cause some viewers discomfort such as dizziness, headache or fatigue of the eyes. It is necessary therefore to prepare a 3DTV broadcasting safety guideline to minimize or remove the cause of such discomfort so safer and more comfortable viewing of 3D broadcasting services is ensured.
1.2 Typical discomforts
Fatigue of eyes
– Unclear vision (vision becoming dim)
– Eyes feeling heavy
– Double vision
– Eyes becoming dry.
– Headache or migraine
– Sickness and nausea
2 Viewing guidelines
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 .
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 .
2.3 Viewing position
Viewers are recommended to face the centre of the display.
– Viewing 3D video directly in front of the display minimizes distortion of scenes. Viewing the video at an oblique angle causes “shear distortion” which is a phenomenon where the 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.
2.3.1 Horizontal viewing position
Viewers are recommended to keep their eyes level with respect to the display.
− If the head of a viewer is inclined considerably to either side (Fig. 1), the binocular disparity of the image is perceived as a vertical parallax into the viewer’s stereopsis system. Therefore, the viewer has 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.
Horizontal viewing position
2.3.2 Right angle viewing position
Viewers should remain at right angles to the display (Fig. 2).
– Viewing a display with the head turned to either side creates a difference in size of image entering the eyes, causing difficulty fusing the two images into a single 3D image.
Right angle viewing position