CN1.Human binocular stereo vision
When humans look at the world around them, they can not only see the width and height of objects, but also know their depth and can judge the distance between objects or between the viewer and the object.
The main reason for this three-dimensional visual characteristic is that people usually always view objects with both eyes at the same time. Due to the distance between the visual axes of the two eyes (about 65 mm), the left eye and the right eye receive different visual images when looking at objects at a certain distance (i.e., parallax). Therefore, the brain combines the information of the two images through the movement and adjustment of the eyeballs to produce a sense of stereo. That is, binocular parallax produces three-dimensionality.
2.3D display
Therefore, if you want people to see 3D images, you must let the left eye and the right eye see different images, so that there is a certain gap between the two images, simulating the actual situation of human eyes watching, so as to show the 3D stereoscopic feeling.
Taking a 3D display as an example, suppose there are three points displayed on the screen: A, B, and C, and each point has two image pairs, left and right, to display the left and right eye images respectively:
- The left eye image Al and the right eye image Ar of point A coincide on the screen. At this time, both eyes see the same image point. The brain will judge that the position of point A is at A’ which coincides with the horizontal plane of the screen;
- The left and right eye images of points B and C do not coincide on the screen. Through the 3D display, the left and right eye images can only be seen by the corresponding eyes. The visual nervous system of the observer’s brain will analyze and fuse the two eye images to form the spatial images of points B and C, and judge that the position of point B is at B’ behind the horizontal plane of the screen, and the position of point C is at C’ in front of the horizontal plane of the screen;
- 3D display screens use the binocular parallax of the human eye to create a sense of depth, or three-dimensionality, at points A, B, and C. The pixel difference between a pair of images on the display screen is called horizontal parallax;
- The left-eye image and the right-eye image at point B are located on the left and right sides of the screen, respectively, which is called positive parallax (sunken into the screen); on the contrary, the left-eye image at point C is located on the right side of the screen, and the right-eye image is located on the left side of the screen, which is called negative parallax (protruding from the screen); and when the images seen by the left and right eyes at point A overlap, the horizontal parallax is 0, which is called zero parallax (located on the screen).
3.3D Video
3D video uses the principle of stereoscopic imaging to allow the left and right eyes to view images with horizontal parallax, and people form a sense of three-dimensionality through the judgment and analysis of the brain.
However, unlike the way we watch in real life, when watching 3-D videos, our eyes must focus on the screen, but objects converge in front of or behind the screen, which results in a convergence-accommodation conflict. When the convergence-accommodation conflict exceeds a certain range, when the horizontal parallax is too large and exceeds the comfort zone, people will feel dizzy and uncomfortable. If the horizontal parallax is too small, the stereoscopic effect will be weakened. Therefore, maintaining a reasonable parallax range is a necessary condition for watching 3-D videos comfortably and obtaining the best 3-D effect.
Factors that affect the visual comfort zone include the size, resolution, viewing distance, and interpupillary distance of the 3D display. In addition, since the visual comfort zone is a subjective statistical concept, for a single user, due to individual differences in age, pupillary distance, vision, etc., people’s sense of stereoscopic comfort also varies from person to person.
By adjusting the display parallax, 3D videos can be adapted to various viewing conditions, while enhancing their stereoscopic effect without causing eye fatigue or dizziness, and users can adjust the stereoscopic effect according to their personal preferences to achieve the best viewing effect.
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