There is a three-dimensional video system that provides a three-dimensional video by showing a video for a right eye and a video for a left eye having a parallax to each observer's left and right eyes. Particularly, a three-dimensional film in which a picture is projected on a large screen can provide entertainment to audiences using films that are very popular.
However, in three-dimensional display based on binocular fusion three-dimensional viewing, it is known that the observer suffers from visual fatigue (Nonpatent Literature 1). In the case of the three-dimensional film, a dual video in which the video for a right eye and the video for a left eye are superimposed is displayed on the screen, and hence the dual video is observed when three-dimensional eyeglasses are removed. The observed dual video increases the observer's fatigue. Thus, when the observer suffers from the visual fatigue caused by binocular fusion three-dimensional viewing, it is difficult to recover from the fatigue by removing the three-dimensional eyeglasses.
However, such visual fatigue does not always occur. Depending on the contents of the three-dimensional video, the degree of visual fatigue varies. Visual fatigue is difficult to occur to those who are good at or accustomed to three-dimensional viewing. However, great visual fatigue occurs to those who are not good at or unaccustomed to three-dimensional viewing. The degree of visual fatigue thus varies depending on an observer's three-dimensional viewing aptitude, creating individual differences.
Patent Literature 1 discloses a three-dimensional video display device that detects reduction of an observer's visual function, and adjusts three-dimensionality of a three-dimensional video based on the degree of fatigue estimated from the detected reduction amount of the visual function. FIG. 1 is a block diagram showing a configuration of the three-dimensional video display device discussed in Patent Literature 1.
Referring to FIG. 1, the three-dimensional video display device includes stereoscopic television (TV) 102, and liquid crystal shutter eyeglasses 101 for viewing a three-dimensional video shown on stereoscopic TV 102. Liquid crystal shutter eyeglasses 101 include electrode 103 for detecting an electro-oculogram (EOG) waveform, and amplifier 104 for amplifying a signal.
Stereoscopic TV 102 includes convergence detection unit 105, counter 106, fatigue calculation unit 107, three-dimensionality adjustment unit 108, and video display unit 109. In stereoscopic TV 102, based on a potential difference signal for a right eye and a left eye transmitted from liquid crystal shutter eyeglasses 101, reduction of a convergence function caused by fatigue of both eyes is detected by convergence detection unit 105 and counter 106. Fatigue calculation unit 107 estimates the degree of eye fatigue based on the detected reduction amount of the convergence function. Three-dimensionality adjustment unit 108 adjusts three-dimensionality based on the estimated degree of fatigue, and video display unit 109 displays a three-dimensional video based on the three-dimensionality adjusted video.
According to the three-dimensional video display device, three-dimensionality can appropriately be set according to the degree of the observer's visual fatigue.
Patent Literature 2 discloses a three-dimensional image display control device that interrupts displaying a three-dimensional video based upon the posture of an observer that indicates that fatigue will occur easily, for example, when the observer tilts his face to view the three-dimensional video. FIGS. 2A and 2B are block diagrams illustrating a configuration of the three-dimensional image display control device discussed in Patent Literature 2.
As shown in FIGS. 2A and 2B, the three-dimensional image display control device includes image switching device 181, image display device 182, shutter eyeglasses 72, left shutter driving device 183L, right shutter driving device 183R, and drive selection device 73.
Image switching device 181 alternately switches image 1L for a left eye and image 1R for a right eye in time division. Image display device 182 displays images switched by image switching device 181. Shutter eyeglasses 72 include shutters 184L and 184R for transmitting or blocking light in association with image switching device 181, and tilt sensor 71 for detecting tilting of the eyeglasses.
Left shutter driving device 183L generates a signal to drive shutter 184L. Right shutter driving device 183R generates a signal to drive shutter 184R. Drive selection device 73 determines, based on a detection result of tilt sensor 71, to which of left shutter driving device 183L and right shutter driving device 183R right shutter 184R is connected.
In the three-dimensional image display control device, when the arrangement direction of left and right eyes of observer 70 matches a horizontal direction, and when image display device 182 displays right eye image 1R, left shutter 184L blocks light while right shutter 184R transmits light. When image display device 182 displays left eye image 1L, left shutter 184L transmits light while right shutter 184R blocks light. Under this control, only left eye and right eye images respectively enter the observer's left and right eyes, enabling three-dimensional observation of the left and right images having a parallax.
When an angle between the arrangement direction of the left and right eyes of observer 70 and the horizontal direction exceeds a predetermined angle, for example, 20 degrees, tilt sensor 71 detects tilting of the eyeglasses. Based on the detected tilting of the eyeglasses, drive selection device 73 connects right shutter 184R to left shutter driving device 183L. Left and right shutters 184L and 184R both transmit light only when image display device 182 displays left eye image 1L, and hence only left eye image 1L enters observer's left and right eyes 70L and 70R. This state is similar to that of viewing not a three-dimensional image but a normal two-dimensional image, and thus no fatigue is generated by binocular fusion three-dimensional viewing.
According to the three-dimensional image display control device, when tilting of the observer's face is detected, by interrupting the displaying the three-dimensional image, the video can be viewed in the state similar to that when the normal video is viewed.
Patent Literature 3 discloses a three-dimensional video playback device that can switch a plane mode and a three-dimensional mode. In the three-dimensional video playback device, a right video and a left video are alternately displayed when the three-dimensional mode is set, and the right video or the left video is displayed when the plane mode is selected.