Human Vision

Human Vision

Nov 15.2012Wu Pei

The eye

Optical system

Cone and Rod Vision:

• In a sense, each of us has two visual systems; the photopic system functions in lighted conditions; the scoptopic system functions in dim light

• Cones mediate photopic vision; rods mediate scotopic vision; this is called the duplexity theory of vision

Distribution of cone and rod

Blind point

Spatial resolution

• 4.5 million cone cells and 90 million rod cells in the human retina in average.

• High resolution in middle and low resolution in edge, highest at fovea, about 1.2'.

• Field of view: best resolution horizontal 35°and vertical 20°

• In all: 1750*1000 in best resolution zone. About 5-15 megapixel whole field

Qualitative representation of visual detail using a single glance of the eyes.

Time resolution

• Persistence of vision: an afterimage is thought to persist for approximately one twenty-fifth of a second on retina.

• Fps: frames per second• The mechanism of film system.

Why game need better fps than movie

• Movie: 24fps TV: 25fps• Game: 59/60fps

Answer

Real video Game

Sensitivity to light• Human eye can is self-adaptive to differed

light intensity by adjusting rhodopsin concentration.

Light sensitivity

Evolutionary perspective

• Our vision is optimized for receiving the most abundant spectral radiance our star emits.

Compared with camera

Contrast sensitivity

Color Depth

• True color :8*3=24 bits• HDR: 32*3=96 bits• HDR use float but not fixed point number for

luminance ranges from 10-4 to 108 . In practice 10bit to encode luminance and 8bit for hue is enough for eliminating quantization error.

Generating HDR Image

Color banding

Hints for video coding

• Human eye is less sensitive to chrominance signal than to luminance signal (U and V can be coarsely coded)

• Human eye is less sensitive to the higher spatial frequency components

• Human eye is less sensitive to quantizing distortion at high luminance levels

Estimating bandwidth of eye

• Input:24bit*10Mpixel*24fps=720MB/s• Output: ~100kB/s• Compare: H.264,1080p:1.5MB/s

How the visual information encoded

• The process of neuron development is a process of “training”.

Encoding and illusion

• Illusion means visually perceived images that differ from objective reality.

• Generally visual encoding is a lossy coding. So look at the illusion will be helpful to know the encoding process.

Mach band: Lateral inhibition

More example: Hermann grid

Thank You