Report itu-r bt. 2293-0 (11/2013)



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4 Subjective measurement of visual discomfort induced by depth characteristics


This experiment assesses the visual discomfort induced by depth magnitude [19]. Psychophysical experiments have been conducted to investigate the relationship between subjective visual comfort and the amount of binocular disparity.

4.1 Visual stimulus


Figure 28 shows an example of the visual stimulus used in this experiment. The visual stimulus consists of two overlapping squares, i.e. foreground and surrounding squares, and background.

The luminance values of the foreground square and the surrounding square were respectively set to 50 cd/m2 and 25 cd/m2 (CIE daylight D65) with afield size of 2º and 10º visual angles.

To avoid the visual effect of the background, the luminance value of the background region was set to 0 cd/m2. The size of the visual field for the foreground square and the surrounding square were determined to cover the size of the fovea and the parafovea respectively. Binocular disparity was only given to the foreground square in the range of +3.7º to –3.7º with a step size of 0.6º, where positive polarity refers to crossed disparity while negative polarity refers to uncrossed disparity.

The range of binocular disparity has been determined in order for a visual comfort model to cover the entire possible range of binocular fusion in real stereoscopic images. The other regions were at zero disparity. Hence, a total number of 13 visual stimuli were randomly presented to human observers.



Figure 28

Visual stimulus used for subjective assessment of the visual discomfort induced
by depth characteristics



4.2 Subjective visual comfort assessment method


A total number of 13 visual stimuli were randomly presented to each subject. The display duration of each visual stimulus was 10 seconds and the resting time followed for 10 seconds using a mid-grey image. During the resting time, subjects assessed the overall level of visual comfort for each visual stimulus. A total of 18 subjects, aged between 20 and 37, participated in this subjective assessment. The subjects were recruited under approval of the KAIST IRB. All subjects had normal or corrected vision and a minimum stereopsis of 60 arcsec (as measured in a stereo fly test).

In order to grade visual comfort, the adjectival categorical judgment method of single stimulus (SS) was used with five-grade scale

5: Very comfortable

4: Comfortable

3: Mildly uncomfortable

2: Uncomfortable

1: Extremely uncomfortable [3].

Further, an additional questionnaire was given to participants, consisting of five representative terms that describe physiological symptoms of visual discomfort: eye strain, general discomfort, nausea, focusing difficulty, and headache [15].

Five-grade scale was used for each questionnaire (5: none, 4: mild, 3: modest, 2: bad, 1: severe). For more details of the subjective assessment methods, refer to § 2.2.

4.3 Experimental results and discussion


Figure 29(a) shows the degree of visual comfort with diverse amount of binocular disparities. In Fig. 29, the x-axis indicates binocular disparity while the y-axis indicates a MOS. As shown in the Figure, human observers reported a higher degree of visual discomfort as the binocular disparity increased. An increase in binocular disparity imposes a higher operating load for the human oculomotor system, which may induce physiological symptoms of visual discomfort [8].

Figure 29(b) represents the degree to which each symptom was obtained from the questionnaire according to the amount of binocular disparity. From these results, it can be observed that as binocular disparity increases, the overall symptoms of visual discomfort (such as focusing difficulty and eye strain) become more severe.



Figure 29

Visual discomfort induced by binocular disparities





(a)

(b)

(a) MOS of visual comfort

(b) The degree of each symptom of visual discomfort.




References

[1] A.J. Woods, “Understanding crosstalk in stereoscopic displays,” In Proceedings of Three‑Dimensional Systems and Applications Conference (3DSA), May 2010.

[2] J.-C. Liou, K. Lee, F.-G. Tseng, J.-F. Huang, W.-T. Yen, and W-L. Hsu, “Shutter glasses stereo LCD with a dynamic backlight,” In Proceedings of SPIE, Stereoscopic Displays and Applications XX, vol. 7237, pp. 72370C-1-72370C-8, January 2009.

[3] Recommendation ITU-R BT-500.11 – Methodology for the subjective assessment of the quality of television pictures, 2002.

[4] Recommendation ITU-R BT.1438 – Subjective assessment for stereoscopic television pictures, 2000.

[5] Y.J. Jung, S. Lee, H. Sohn, H.W. Park, and Y.M. Ro, “Visual comfort assessment metric based on salient object motion information in stereoscopic video,” Journal of Electronic Imaging, vol. 21, No. 1, 2012.

[6] D.L. Macadam, “Visual sensitivities to color differences in daylight,” Journal of the Optical Society of America 32(5), 247-274 (1942).

[7] F. Speranza, W.J. Tam, R. Renaud, and N. Hur, “Effect of disparity and motion on visual comfort of stereoscopic images,” Proc. SPIE 6055, pp. 94-103, 2006.

[8] M. Lambooij, W. Ijsselsteijn, M. Fortuin, I. Heynderickx, “Visual discomfort and visual fatigue of stereoscopic displays: a review,” J. Imaging Sci. Technol. 53(3), 1-14 (2009).

[9] S. Yano, S. Ide, T. Mistuhashi, and H. Thwaites, “A study of visual fatigue and visual comfort for 3D HDTV//HDTV images,” Displays 23(4), 191-201 (2002).

[10] F.L. Kooi, A. Toet, “Visual comfort of binocular and 3D displays,” Displays 25, 99-108 (2004).

[11] S. Yano, M. Emoto, and T. Mitsuhashi, “Two factors in visual fatigue caused by stereoscopic HDTV images,” Displays 25, 141-150 (2004).

[12] M. Lambooij, M.F. Fortuin, W.A. Ijsselsteijn, and I. Heyndericks, “Visual discomfort associated with 3D displays,” Fifth International Workshop on Video Processing and Quality Metrics for Consumer Electronics 2010, (2010).

[13] W.J. Tam, C. Vázquez, and F. Speranza, “Three-dimensional TV: A novel method for generating surrogate depth maps using colour information,” Proceedings of SPIE 7237, (2009).

[14] S. Yano, M. Emoto, and T. Mitsuhashi, “Two factors in visual fatigue caused by stereoscopic HDTV images,” Displays 25, 141-150 (2004).

[15] R.S. Kennedy, N.E. Lane, K.S., Berbaum, and M.G. Lilienthal, “Simulator sickness questionnaire: an enhanced method for quantifying simulator sickness,” International Journal of Aviation Psychology, vol. 3, No. 3, pp. 203-220, 1993.

[16] F.L. Kooi, A. Toet, “Visual comfort of binocular and 3D displays,” Displays 25, 99-108 (2004).

[17] Z. Zhe and H.R. Wu, “A ratio-sensitive image quality metric,” in Proc. IEEE International Symposium on Intelligent Signal Processing and Communication Systems, pp. 362-364, Nov. (2004).

[18] M.W. Levine, Fundamentals of sensation and perception, 3rd ed., Oxford University Press, New York (2000).

[19] H. Sohn, Y.J. Jung, S. Lee, H.W. Park, and Y.M. Ro, “Attention model-based visual comfort assessment for stereoscopic depth perception,” International Conference on Digital Signal Processing (DSP), pp. 1-6, 6-8 July 2011.



Annex 6

The influence of stereopsis and abnormal binocular vision on ocular and systemic discomfort while watching 3D television – Korea (Republic of)


1 Summary and proposals


In preliminary experiments, it was observed:

– Subjects with abnormal binocular vision such as strabismus, amblyopia, and anisometropia showed decreased 3D perception.

– Ocular and systemic discomforts (3D fatigue) were more related to a higher degree of stereopsis.

– Those with abnormal binocular vision are more susceptible to 3D fatigue if they have a normal degree of stereopsis.

– If a person cannot perceive 3D, or feels severe 3D fatigue while watching 3D content, he or she should consult ophthalmologic specialists for evaluation of abnormal binocular vision.

These observations should be referred to when developing viewing safety guidelines of stereoscopic 3D systems.


2 Abstract


Perception of a three-dimensional (3D) image involves a fusional mechanism. With normal binocular vision, one can perceive 3D images with motor and sensory fusion. People with abnormal binocular vision, including strabismus, amblyopia, and anisometropia, may have a variable range of fusional ability. Some people cannot use a fusional mechanism at all, and others can only use a fusional mechanism to a normal degree with an additive effort to obtain it.

This kind of additive effort can increase fatigue while watching 3D images (which is known as 3D fatigue). In addition, the degree of abnormal binocular vision, which can be measured with a stereopsis test, can affect the degree of 3D perception. Yet, the degrees of 3D perception and 3D fatigue in abnormal binocularity have not been evaluated in comparison with normal binocularity.

The purpose of this study is to evaluate the degree of 3D perception and ocular and systemic discomfort in people with abnormal binocular vision, including strabismus, amblyopia, and anisometropia, and their relationship to stereoacuity while watching a 3D television.

3 Participants and methods


Children 9 years of age or older, who had at least one abnormal binocular condition, including strabismus, anisometropia, and amblyopia, were recruited for the abnormal binocular vision (ABV) group.

Subjects without those abnormal conditions were included in the control group. Anisometropia was defined as when the difference of the spherical equivalent (SEQ) in refractive errors between both eyes was more than 2 diopters. Amblyopia was diagnosed as when the best-corrected visual acuity was less than 0.8, or when the difference between both eyes was more than two lines of Snellen acuity. The ABV group was divided into three subgroups according to the etiology of their ABV. When a person was strabismic or had anisometropic amblyopia, he or she was included in the amblyopia subgroup for analysis. Informed consent was obtained from all of the volunteers. Volunteers with a history of other ophthalmologic diseases, including glaucoma and retinal disease, and with systemic diseases, such as cerebral palsy and delayed maturation, were excluded.

The best-corrected visual acuity and refractive errors were measured. The angle of ocular deviation was obtained with the alternate prism-cover test. Stereoacuity was examined with the Stereo Fly test (Stereo Optical Co., Chicago, IL, USA) for near stereopsis and with the Frisby-Davis distance stereotest (FD2; Stereotest, Sheffield, UK) for distant stereopsis. The fundus was also checked with a fundus camera.

The 3D video, which was produced by the national broadcasting system of South Korea, was shown for 20 minutes on a 55-inch 3D high-definition television. The room was illuminated to 5 lux. The viewing distance was 2.8 metres. The volunteers watched 3DTV with shutter glasses or Polaroid glasses according to the type of 3DTV.

After watching 3DTV, a survey was performed to evaluate the degree of 3D perception and the subjective symptoms of ocular and systemic discomfort (Table 13). The questionnaire was comprised of 13 items, which included the degree of 3D perception and frequently reported ocular and non-ocular symptoms after watching 3DTV. Each item was answered according to a six‑category scale (0-5). A value of 0 corresponded to no impact and a value of 5 corresponded to an impact too severe to watch 3DTV. The degree of 3D perception and subjective ocular and systemic discomforts were compared between the two groups.

The stereoacuity results were grouped as either "normal" (≤ 60 arcsec), "moderate" (> 60 and ≤ 800 arcsec), or "poor" (> 800 arcsec to nil) stereopsis according to the amount of stereoacuity. The degree of 3D perception and the number of ocular and systemic symptoms were compared among the stereoacuity groups. Those things were also compared between the subjects who showed normal stereopsis in the ABV group and in the control group.

For statistical analysis, Kruskal-Wallis and Mann-Whitney U tests were used with SPSS 12.0K for Windows. For multiple testing problems, P values were adjusted with Bonferroni correction. To compare the distribution of the subjects in the near stereoacuity case, a chi-square test was used.

4 Results


One hundred and thirty subjects were enrolled in this study, with 98 in the ABV group and 32 in the control group. The mean age of the subjects was 13.0 ± 4.87 years. Seventy-five (57.7%) subjects were female. The ABV group included 49 people with strabismus, 22 with amblyopia, and 27 with anisometropia. In strabismic people, 34 had exodeviation, 11 had esodeviation, and 4 had hyperdeviation. The mean deviation angles (prism diopters) among those people were 11.6 ± 6.74, 7.7 ± 14.72, and 5.5 ± 5.74, respectively. In amblyopic people, the mean visual acuity of the worse eye was 0.58 ± 0.27. In anisometropic people, the mean difference of the SEQ between the two eyes was 2.71 ± 1.58.

The mean stereoacuity at a distance was 14.06 ± 9.79 arcsec in the control group and 34.85 ± 16.32 arcsec in the ABV group (P < 0.001). There were no subjects with poor distant stereopsis measured with FD2. For near stereoacuity, all subjects in the control group showed normal stereopsis, and 53 people of the ABV group had normal, 33 had moderate, and the other 12 had poor near stereopsis. Thus, there was a significant difference in the distribution of near stereoacuity between the two groups (P < 0.001). In the ABV group, the mean distant stereopsis was 31.02 ± 16.99 in the strabismus subgroup, 45.00 ± 11.95 in the amblyopia subgroup, and 33.52 ± 15.12 in the anisometropia subgroup (P < 0.001).

The distant stereoacuity of the amblyopia subgroup was poorer than that in the strabismus (P = 0.006) and anisometropia subgroups (P = 0.012). There was no difference between the strabismus and anisometropia subgroups (P = 0.556). The distribution of near stereoacuity was not significantly different among the subgroups of the ABV group (P = 0.126). In the strabismus subgroup, the exotropic group showed better stereoacuity at near and distant fixation than the esotropic group (P < 0.001).

The results of the survey showed that the ocular and systemic discomforts were not different between the ABV and control group. The ABV group showed decreased 3D perception (P = 0.007).

Subgroup analysis revealed that there was no difference among subjects with strabismus or anisometropia and the control group. Subjects with amblyopia showed more decreased 3D perception than the others (P < 0.05). Among the subjects with strabismus, exotropic people reported more discomfort than esotropic people (P < 0.05).

The ocular and systemic discomforts were compared according to the amount of stereoacuity. The subjects with good stereopsis (as measured with a Titmus stereofly test) reported more dizziness, headaches, eye fatigue, and pain (P < 0.05) than the other subjects with decreased stereopsis (> 60 arcsec). The subjects with decreased stereopsis showed more difficulty in 3D perception (P < 0.001).

There was no difference in the amount of ocular and systemic discomfort between the subjects with moderate stereopsis and with poor stereopsis. Subjects with poor stereoacuity showed more difficulty in 3D perception than those with moderate stereoacuity.

Among subjects with good stereopsis, those in the ABV group felt more eye fatigue than those in the control group (P = 0.031); those subjects also experienced more headaches than those in the control group to a marginally significant degree (P = 0.076).


5 Discussion


Generally, a subject with ABV may have difficulty perceiving 3D images. For sensory fusion to occur, the images located on the corresponding retina must be similar in size, colour, and sharpness. Unequal observed images are a severe sensory obstacle to fusion.

If a person has anisometropia or amblyopia, the quality of observed images can be unequal, and this might disturb sensory fusion. A person with strabismus can have problems in both sensory and motor fusion. Those problems decrease stereopsis, which can be measured with a stereoacuity test. The decrease of stereoacuity can vary according to the degree of binocular abnormality and fusional ability. A person with binocular abnormality can show normal stereoacuity if his or her fusional amplitude is large enough to overcome the abnormality. However, it is possible that maintaining fusion can induce more fatigue and discomfort despite the presence of ABV.

In this study, there was no difference in the amount of ocular and systemic discomfort between the ABV and control groups. The presence of abnormality in binocular vision itself did not play an important role in symptoms after watching 3DTV. However, the ABV group showed variable degrees of stereopsis. 45 subjects of the ABV group showed moderate to poor near stereoacuity, but the other 53 in the ABV group showed normal near stereoacuity. When ocular and systemic discomfort according to the amount of stereoacuity was evaluated, subjects with normal stereopsis experienced more discomfort than those with moderate to poor stereopsis, although they perceived stereoscopic images better. We believe that the subjects with moderate to poor stereopsis had difficulty in fusion while watching 3DTV. That might have made the 3D images indistinguishable from the 2D images for them, and they did not experience more ocular and systemic symptoms.

Among the subjects with normal stereopsis in both groups, the subjects of the ABV group experienced more ocular fatigue than those of the control group. They had more headaches with marginal significance. We think that those subjects should make additional efforts, such as fusional vergence and accommodation, to maintain fusion while watching 3DTV.

Fusional vergence is needed to perceive two images with horizontal disparity as one stereoscopic image when watching a 3DTV. Accommodation is accompanied by vergence of eye movement, which is unnecessary, because the distance between the eyes and the 3D display screen does not change. This vergence-accommodation conflict was reported as an important factor in so-called 3D fatigue.

If a subject used more vergence while watching 3D images, they experienced more fatigue than the others. Emoto et al. reported that fusional amplitude showed a greater decrease in stereoscopic viewing than in viewing conventional TV. Although some with strabismus, anisometropia, or amblyopia showed normal stereoacuity, we believe they might have experienced more ocular and systemic discomfort while watching 3DTV.

In conclusion, ocular and systemic discomforts were more related to better stereopsis, although subjects with ABV showed decreased 3D perception. Subjects with binocular visual abnormalities such as strabismus, amblyopia, and anisometropia, are more susceptible to ocular and systemic discomfort if they have good stereopsis. Therefore, we recommend that if people have asthenopic symptoms or do not experience depth perception while watching 3DTV, they need to get their eyes aligned and checked for stereopsis.

TABLE 13


Questionnaire




0

1

2

3

4

5

Dizzy



















Headache



















Nausea



















Eye fatigue



















Eye pain



















Tearing



















Eye dryness



















Blurred vision



















Difficulty in focusing



















Double vision



















Transient visual dimness after watching TV



















Couldn't feel stereoscopic vision



















Difficulty in eye tracking the motion on TV



















0: never experienced 3: severe impact

1: mild impact 4: very severe impact

2: moderate impact 5: too severe of an impact to watch 3DTV

Annex 7

The influences of Parkinson’s diseases on dynamic 3D perception and fatigue
while watching 3D television – Korea (Republic of)

1 Introduction and study results


Stereopsis is an awareness of the distances of objects from an observer. Binocular vision is necessary to perceive stereopsis. Therefore, stereopsis is often used to refer to binocular depth perception. For this to occur, many components of stereopsis such as retina disparity, eye movement, primary perception of brain and functions of image processing are necessary.

People with Parkinson’s disease (PD) 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. A loss of dopaminergic neuronal cells, as found in the inner nuclear and inner plexiform layers of the human retina, has been found in those with PD. In terms of eye movement, convergence amplitudes are significantly poorer in PD group than in control subjects. In the brain, the amount of visual attention, as well as the type of visual and spatial perception, decreases in those with PD.

These impairments can lead to poorer cognitive functioning. For these reasons, we assumed that retinal problems, eye movement, and the brain cognitive functions of people with PD can affect the level of stereopsis. As such, we have developed a method to easily evaluate the degree of stereopsis (especially dynamic stereopsis) that can be observed when people with DP are watching 3‑dimensional television (3D V).

PD patients are known to perceive visual stimuli poorly and some researchers have reported that they experience a lower stereopsis function than normal control subjects when taking the Titmus fly test. Because of these problems, we analysed stereopsis and fatigue of people with PD, who have intact stereoacuity, while they were watching 3DTV. Forty-eight subjects with PD and thirty-two age-matched controls were enrolled. Before watching 3DTV, we examined visual acuity, the angle of strabismus, and refractive errors, and we performed the static stereopsis test (Titmus fly test) and the cognitive function test. We used a 17-minute 3D movie, and conducted a questionnaire to measure subjective dynamic 3D perception and 3D fatigue while watching 3DTV.

In this study, subjective dynamic 3D perception was not considered distinct from the PD patients to the control subjects, generally. However, in a subgroup analysis of those with PD, the severity of the disease correlated to subjective dynamic stereopsis in the PD patients. In terms of safety, 3D fatigue is not distinct from the control subjects to the PD patients. Therefore, most people with PD can experience 3D effects without experiencing 3D fatigue. However, the severity of PD can affect dynamic 3D perception even though viewers may have intact stereoacuity. For more information about these experiments, please see Attachment to Annex 7.

2 Summary and proposals


In preliminary experiments, it was observed:

• Those with Parkinson’s disease (PD) can sufficiently experience 3D effects.

• However, the severity of PD can affect dynamic 3D perception.

• In terms of safety, watching 3DTV is not harmful for people with PD if they comply with the “3D video safety guidelines”.

These observations should be considered when developing viewing safety guidelines for stereoscopic 3D systems.

Attachment

Subjects and methods

Subjects were recruited with Parkinson’s disease (PD) and also as age-matched normal control subjects. All subjects showed stereoacuity levels of under 800 arcsec. Informed consent was obtained from all of the patients and control subjects.

The levels of visual acuity and number of refractive errors were measured. The angle of ocular deviation was obtained by using the alternate prism-cover test. Stereoacuity was examined with the Stereo Fly test (Stereo Optical Co., Chicago, IL, USA) for near stereopsis.

The 3D video, which was produced by the national broadcasting system of South Korea, was shown for 17 minutes on a 55-inch 3D high-definition television. The viewing distance was 2.7 metres. After watching 3DTV, a survey was performed to evaluate the degree of subjective 3D perception.

The questionnaire was comprised of six items, which included the degree of 3D perception and also some frequently reported symptoms after watching 3DTV (Table 14). Each item was answered according to a five-category scale (1-5). A value of 1 corresponded to no impact and a value of 5 corresponded to an impact too severe to watch 3DTV. The degree of subjective 3D perception and level of discomfort were compared between the three groups.

For statistical analysis, the Independent-Samples Kruskal-Wallis Test and Kendall’s Tau correlation were used with SPSS 20.0K for Windows.

Experimental results and discussion


Eighty subjects were enrolled in this study. There were 48 people with PD and 32 age-matched normal subjects. The mean age between the two groups was 67.3 ± 9.76 and 65.6 ± 9.71 years, respectively. The mean cognitive function test (MoCA) between the two groups was 21.9 ± 5.17 and 24.4 ± 3.00, respectively. Cognitive function tests were significant between the PD group and the control subjects (P = 0.018).

The mean subjective dynamic 3D perception score of the PD group was similar to that of the control subjects (4.06 ± 1.19 vs. 3.90 ± 1.34, respectively). These scores show that people with PD can perceive dynamic 3D content as well as normal control subjects. However, this finding correlated with the H-Y stage (= 0.253, P = 0.048). The more severe the condition, the lower their subjective 3D perception scores were. From the results, it can be inferred that those with severe PD might experience a small 3D effect even if they do not have any problems in their eyes.

There was no difference in the amount of 3D fatigue between the two groups except significantly in terms of eye fatigue. Although those with PD felt more eye fatigue than the control group, the mean score reflected a mild impact (2.21 ± 1.05). Therefore, in terms of safety, 3DTV can be considered not bad for PD patients.

TABLE 14


Questionnaire

Item

1

2

3

4

5

Dizzy
















Headache
















Nausea
















Eye fatigue
















Cold sweat
















Feel stereoscopic vision
















*1: never experienced, 2: mild impact, 3: moderate impact, 4, severe impact, 5: very severe impact



References

T. Müller, D. Woitalla, S. Peters, K. Kohla, and H. Przuntek, “Progress of visual dysfunction in Parkinson’s disease,” Acta Neurologica Scandinavica, Vol. 105, pp. 256‑260, 2002.

S.H. Kim, J.H. Park, Y.H. Kim, and S.B. Koh, “Stereopsis in drug naive Parkinson’s disease patients,” Can J Neurol Sci, Vol. 38, pp. 299-302, Mar 2011.

Annex 8

Visual discomfort induced by the binocular disparity of


stereoscopic video – Korea (Republic of)

1 Introduction and study results


One of the biggest reasons that people lost their interest in stereoscopic images was the visual discomfort they experienced while watching 3D content. Therefore, 3D watching safety guidelines should be considered to commercialize 3D broadcasting content if producers expect to achieve long hours of repeated watching.

Positive disparity, negative disparity, depth budget, and depth motion cause inconsistency of accommodation and vergence in the creation of stereoscopic 3D content, and 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. Therefore, to assess the visual comfort level depending on the level of binocular disparity, the main properties of binocular disparity were designed to have five different levels and 3D content was created for each level. An experiment with 100 participants was performed with the subjective quality assessment method recommended by Recommendations ITU-R BT.500-11 and ITU-R BT.1438.

The experimental results showed some differences in visual discomfort depending on the positive disparity, negative disparity, maximum relative disparity, and change rate of binocular disparity. Binocular disparity was the fundamental element present in the stereoscopic images, but the excessive amount was the main cause of visual discomfort in the perception of those images. Additionally, the changing rate of binocular disparity affected the visual discomfort level.

2 Summary and proposals


This annex describes the allowable range of visual discomfort with respect to positive disparity, negative disparity, depth budget, and the motion change by disparity. Based on subjective assessment, the following aspects have been considered for the production guidelines of stereoscopic 3D video.

– Excessive positive disparity, excessive negative disparity, and excessive depth budget cause excessive screen disparity in 3DTV applications, and hence the content may not be perceived as 3D and can cause visual discomfort. Therefore, care while 3D watching is recommended.

– The high level of the change rate of binocular disparity in videos with depth motion may cause visual discomfort. Therefore, care while 3D watching is recommended.

These observations should be considered when developing viewing safety guidelines for stereoscopic 3D systems.


Attachment

Results of subjective visual comfort assessment for disparity


and motion depth magnitude of 3D content

1 Experimental environments


A 55-inch circular polarized 3DTV(LG Electronics, Korea) was used to present 3D images to participants. The resolution was set to 1 920 × 1 080 pixels, and the viewing distance was maintained at 2.7 m, which is three times the screen height of the TV. Figure 30 shows the viewing environment of the subjective measurement test. All experimental environments followed Recommendations ITU-R BT.500-11 [2] and ITU-R BT.1438 [3]. Table 15 is a summary of the experimental environment. This study was arranged to simulate the viewing environment of a typical household because the objective of the study was to measure the effect of 3DTV viewing at home.

Figure 30



Stereoscopic 3D monitor used in our subjective assessments

TABLE 15


Experimental environment home table




Recommendation ITU-R BT.500-11

Ours

Environmental illumination

200 lux

210 lux

Maximum observation angle

Maximum 30

Maximum 21.8

Peak luminance

≥ 200 cd/m2 (45 lux)




Height of display (H)




726 mm

Viewing distance




3H (2.7 m)



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