Human Vision
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Transcript of Human Vision
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Human Vision
Nov 15.2012Wu Pei
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The eye
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Optical system
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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
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Distribution of cone and rod
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Blind point
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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
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Qualitative representation of visual detail using a single glance of the eyes.
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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.
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Why game need better fps than movie
• Movie: 24fps TV: 25fps• Game: 59/60fps
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Answer
Real video Game
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Sensitivity to light• Human eye can is self-adaptive to differed
light intensity by adjusting rhodopsin concentration.
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Light sensitivity
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Evolutionary perspective
• Our vision is optimized for receiving the most abundant spectral radiance our star emits.
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Compared with camera
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Contrast sensitivity
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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.
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Generating HDR Image
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Color banding
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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
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Estimating bandwidth of eye
• Input:24bit*10Mpixel*24fps=720MB/s• Output: ~100kB/s• Compare: H.264,1080p:1.5MB/s
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How the visual information encoded
• The process of neuron development is a process of “training”.
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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.
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Mach band: Lateral inhibition
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More example: Hermann grid
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Thank You