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04/19/23 Visualization Laboratory, Texas A&M University
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ENDS 375
Foundations of Visualization
9/20/05 Notes
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04/19/23 Visualization Laboratory, Texas A&M University 2
Image Statistics
Useful input into computational algorithms
–measures of image quality
–basis for automated decisions about images
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04/19/23 Visualization Laboratory, Texas A&M University 3
Image Statistics
Arithmetic Meanmean = sum(Pxy)/(x*y)
Variance
variance = (sum(Pxy*Pxy)/(x*y)-mean*mean)
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04/19/23 Visualization Laboratory, Texas A&M University 4
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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04/19/23 Visualization Laboratory, Texas A&M University 5
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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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04/19/23 Visualization Laboratory, Texas A&M University 7
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
LessRed
MoreYellow
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04/19/23 Visualization Laboratory, Texas A&M University 11
Arithmetic Operations
Two or more images
Cxy = Axy < operation > Bxy
– Addition
– Subtraction
– Averaging, etc ...
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04/19/23 Visualization Laboratory, Texas A&M University 12
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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04/19/23 Visualization Laboratory, Texas A&M University 14
Alpha Blending
Cxy = Axy*Mxy
+ Bxy*(max -Mxy )
“Blends” two images
Need a “matte” imageBasis for image compositing
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Compositing
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04/19/23 Visualization Laboratory, Texas A&M University 16
Readings
Course notes section 1-7 Course notes section 1-8