ENDS 375

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ENDS 375

• Foundations of Visualization
• 9/20/05 Notes

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Image Statistics

• Useful input into computational algorithms
• measures of image quality
• basis for automated decisions about images

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Image Statistics

• Arithmetic Mean
• mean sum(Pxy)/(xy)
• Variance
• variance (sum(PxyPxy)/(xy)-meanmean)

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Image Statistics

• Standard Deviation
• stdev square root (variance)
• Histogram
• two axis plot of pixel values vs number of
  pixels
• basis for deciding - contrast range, overall
  brightness, thresholding, ...

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Point Operations on Images

• Numeric Transformation
• (often not reversible)
• Transfer Functions
• Often implemented using look-up tables

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Specific Operations

• Unity
• Invert

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Specific Operations

• Contrast Adjustment
• Higher
• Lower

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Specific Operations

• Threshold
• Gamma

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Color Modification

• Less
• Red
• More
• Yellow

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Arithmetic Operations

• Two or more images
• Cxy Axy lt operation gt Bxy
• Addition
• Subtraction
• Averaging, etc ...

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Logical Operations

• and, or
• nand, nor
• xor, xnor

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Image Averaging

• Add corresponding pixels from multiple images
  then divide by the number of images

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Alpha Blending

• Cxy AxyMxy
• Bxy(max -Mxy )
• Blends two images
• Need a matte image
• Basis for image compositing

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Compositing
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Readings

• Course notes section 1-7
• Course notes section 1-8