ENDS 375

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ENDS 375

• Foundations of Visualization
• 9/6/05 Class Notes

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Human Vision

• Structure of the Eye
• Image Formation in the Eye
• Brightness Adaptation

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Eye Structures

• Cornea and sclera
• Choroid
• Retina (light sensors)
• Rods and Cones
• Ciliary and iris
• Lens (focus the image)

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Structure of the Eye
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Retina

• Rods
• 75-150 million
• no color
• low light (scotopic)
• Cones
• 6-7 million (fovea)
• color
• bright light (photopic)

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Image Formation
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Brightness Adaptation
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The Digital Image

• Why Bother with Digital Images?
• Image generation - image synthesis
• Image Manipulation
• Image data compression
• lossy, lossless

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The Digital Image

• Real vs digital images
• Sampled array, pixels, ...
• Analog Eyes and Discrete Digital Images
• Spatial resolution
• Color depth - binary, gray scale, ...
• Color representation - RGB, HSV,
• components, channels

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Digital Image

• A Little History
• TransAtlantic Photos
• Space Program
• Medical Imaging, etc ...
• Entertainment

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Digital Image Processing

• Used to extract image information
• for machine perception, recognition, ...
• Histograms, patterns, etc
• Used to visually enhance images
• sharpen, reduce noise, false colors,

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Digital Image Processing

• Make information from non-visual sensors visible
• x-ray and MRIs
• infrared and ultraviolet
• sonograms, etc ...

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Resolution Image

• Spatial Resolution
• Depth Resolution
• Spatial vs Depth Tradeoff

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Spatial Resolution

• (0,0) usually at the upper left corner
• X to the right, Y down

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Spatial Resolution
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Depth Resolution

• Color encoding
• gray, color, which space?

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Spatial vs Depth Tradeoff

• Halftoning
• Approximate higher depth resolution with
  clusters of lower depth pixels
• Increases the pixel size of the image

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Image manipulation

• Input image
• -gt operation
• -gt output image

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Image manipulation

• Thresholding
• Contrast, brightness, color manipulations
• Filtering
• convolution - blurring, sharpening, median, ...

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Image manipulation

• Geometric - scaling, translation, rotation, 3D
• Warping/morphing
• Multiple image operations
• addition, difference, mattes,

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Image Formation

• Usually created by projecting a 3D environment
  or scene onto a 2D image surface
• for a camera
• Scene gt lens gt film plane
• for the computer
• 3D model gt renderer gt 2D image

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An Image Model

• Two dimensional light intensity function
• f(x,y) I(x,y) r(x,y)
• illumination 0 lt i(x,y) lt infinity
• reflection 0.0 lt r(x,y) lt 1.0
• Example illumination values (ft-candles)
• sunny 9000, cloudy 1000, office 100
• Example reflection values
• snow .93, white paint .8, black velvet .01

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Sampling

• Spatial grid
• Discrete
• Uniform
• Specific size

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Quantization

• color or gray scale (continuous)
• into color or gray levels (discrete)
• image data size
• N x M x m
• (spatial size x depth)

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Quantization

• how many levels?
• depends on application?
• need spatial resolution?
• need color resolution or both?
• need speed or small file size?

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Reading

• Course notes
• Section 1-1 (human vision)
• Section 1-2 (digital image)
• Section 1-3 (an image model)
• Additional readings
• As listed