Notes from Edx’s VR Certificate course
Week 1 (cont..)
1. Monocular 3D Cues
- Monocular 3D Cues: means how the human eye can estimate depth with even one eye closed
- Figuring out relative sizes: We compare the relative sizes of objects on our retina with the other retina. Smaller objects are thought to be further away from us
- Objects closer to the horizon are further away
- Oclusion: strong depth cue
- Linear perspective: depth cue. Straight lines that meet in one point, are thought to be parallel, and only appear to converge, because they disappear in the distance.
- Shadow: depth cue
- Moving parallax
- Depth cue: called accomodation which puts objects in focus
2. Stereo Vision
- When we look at an object, no matter how far, each one of our eyes turns towards it. Objects that are further away make our eyes turn inward less, than objects that are closer
- Depending on how inwards the eyes turn, the brain determines how far away the object is from us (Accommodation)
- Accomodation vs Convergance: To accommodate, the eye changes the shape of the lens. Convergence is the amount of turn-in.
- Binocular Disparity: When objects arent at the same distance, they appear as double images
- Convergence is the strongest depth cue
3. How human perceive color
- The eyes are sensors for electromagnetic waves
- Along the electromagnetic spectrum, visible light is nestled in between Ultraviolet and Infrared light
- Objects reflect different wavelengths at different intensities
- Every object has its own reflectance spectra
- How do our eyes perceive the light spectrum? : There are 4 types of photoreceptor cells that detect light on the retina. These cells are 2 rods and 3 types of cones. These photoreceptor cells are dense enough for us to see a resolution of 150 pixels per degree in the center of our view. This is where our vision is the clearest. Rods sense light intensity and Cones detect wavelengths. Rods are dominant in number in low light settings, so we lose color vision (cones) in the darkness.
- Trihromatic Theory: Each one of the 3 types of ones is responsible for a different subset of the visible light spectrum. One cone is responsible for red light, the 2nd one for green and the 3rd one for blue [RGB]
- To optimally be able to represent the light spectrum humans can see, all our displays composite color images out of three basic colors: red, green and blue.
- Field of view: This is another parameter needed to display VR. The combined field of view between both eyes is up to 220 degrees. In the center of our vision is 120 degree field, which both eyes can see, and this is where binocular vision is, meaning that we can see the world in 3D stereo in these 120 degrees.
- Temporal resolution: our eyes can distinguish up to 150 different frames per second
4. Stereo Display Technologies
- How to generate images so that our eyes convergance mechanism is activated. As Convergence is the strongest depth cue.
- For convergence, we need to show each eye a slightly offset image of the same scene, so that we need to show each eye a separate image. A simple way to do this is to have each eye look at a different image by showing a different image to each eye.
- Methods to view 3D stereo have been developed. For example anaglyph stereo.
- Many of you have probably seen these pictures that are mostly red and blue or red and green, but when you put glasses with lenses in matching colors on, you can see the image in 3D.
- By crossing eyes via focusing on your finger or another object, a 3D image is produced
- So essentially you’re converging your eyes on a point that is infront of the image plane
- Another example of methods to view 3D images without headgear is stereograms.
- The approach to view them is the same. Viewing imagess side by side images, except that the two images have been combined into one.
- Method # 3 to view 3D images: Active stereo.
- Method #4 to view 3D images: Passive stereo
- Ghosting: liquid crystals used in active stereo and the polarization filters used in passive stereo don’t block out light from the unwanted image completely.
- Ghosting remedied by a patent developed by a company called Infitec
- Autostereos optic displays: view 3D images without glasses. These displays have a special layer over a regular LCD display to direct the light from the pixels to only one of the user’s eyes. Example Nintendo 3DS