Download - ENDS 375
04/19/23 Visualization Laboratory, Texas A&M University
1
ENDS 375
Foundations of Visualization
9/20/05 Notes
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
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)
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, ...
04/19/23 Visualization Laboratory, Texas A&M University 5
04/19/23 Visualization Laboratory, Texas A&M University 6
Point Operations on Images Numeric Transformation
– (often not reversible) Transfer Functions Often implemented using look-up tables
04/19/23 Visualization Laboratory, Texas A&M University 7
Specific Operations
Unity
Invert
04/19/23 Visualization Laboratory, Texas A&M University 8
Specific Operations
Contrast Adjustment
Higher
Lower
04/19/23 Visualization Laboratory, Texas A&M University 9
Specific Operations
Threshold
Gamma
04/19/23 Visualization Laboratory, Texas A&M University 10
Color Modification
LessRed
MoreYellow
04/19/23 Visualization Laboratory, Texas A&M University 11
Arithmetic Operations
Two or more images
Cxy = Axy < operation > Bxy
– Addition
– Subtraction
– Averaging, etc ...
04/19/23 Visualization Laboratory, Texas A&M University 12
Logical Operations
and, or
nand, nor
xor, xnor
04/19/23 Visualization Laboratory, Texas A&M University 13
Image Averaging
Add corresponding pixels from multiple images then divide by the number of images
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
04/19/23 Visualization Laboratory, Texas A&M University 15
Compositing
04/19/23 Visualization Laboratory, Texas A&M University 16
Readings
Course notes section 1-7 Course notes section 1-8