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L16post

# L16post - Previous Lecture Working with images Todays...

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Previous Lecture: Working with images Today’s Lecture: More on manipulating images “Noise” filtering Edge finding Announcements: Project 4 due tonight at 11pm

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October 22, 2009 Lecture 16 4 An image as an array: values in [0..255] 150 149 152 153 152 155 151 150 153 154 153 156 153 151 155 156 155 158 154 153 156 157 156 159 156 154 158 159 158 161 157 156 159 160 159 162 0 = black 255 = white These are integer values Type: uint8
October 22, 2009 Lecture 16 6 Vectorized code to create a mirror image A = imread(’LawSchool.jpg’) [nr,nc,np] = size(A); for c= 1:nc B(:,c,1) = A(:,nc+1-c,1) B(:,c,2) = A(:,nc+1-c,2) B(:,c,3) = A(:,nc+1-c,3) end imwrite(B,'LawSchoolMirror.jpg') Can i mp ro v e efficiency by initializing B to be a 3 -d array of the app rop riate size

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October 22, 2009 Lecture 16 7 Example: produce a negative
October 22, 2009 Lecture 16 8 Problem: produce a negative “Negative” is what we say, but all color values are positive numbers! Think in terms of the extremes, 0 and 255. Then the “negative” just means the opposite side . So 0 is the opposite of 255 ; 1 254 ; 5 250 ; 30 225 ; x 255-x

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October 22, 2009 Lecture 16 9 function newIm = toNegative(im) % newIm is the negative of image data im % im, newIm are 3-d arrays; each component is uint8 [nr,nc,np]= size(im); % dimensions of im newIm= zeros(nr,nc); % initialize newIm newIm= uint8(newIm); % Type for image color values for r= 1:nr for c= 1:nc for p= 1:np newIm(r,c,p)= ___________________; end end end
October 22, 2009 Lecture 16 10 function newIm = toNegative(im) % newIm is the negative of image im % im, newIm are 3-d arrays; each component is uint8 [nr,nc,np]= size(im); % dimensions of im newIm= zeros(nr,nc,np); % initialize newIm newIm= uint8(newIm); % Type for image color values for r= 1:nr for c= 1:nc for p= 1:np newIm(r,c,p)= 255 - im(r,c,p); end end end

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October 22, 2009 Lecture 16 11 150 149 152 153 152 155 151 150 153 154 153 156 153 2 3 156 155 158 154 2 1 157 156 159 156 154 158 159 158 161 157 156 159 160 159 162 Dirt in the image! Note how the “dirty pixels” look out of place
October 22, 2009 Lecture 16 12 Clean up “noise” — median filtering

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October 22, 2009 Lecture 16 13 150 149 152 153 152 155 151 150 153 154 153 156 153 ? ? 156 155 158 154 ? ? 157 156 159 156 154 158 159 158 161 157 156 159 160 159 162 Assign “typical” neighborhood gray values to “dirty pixels” What to do with the dirty pixels?
October 22, 2009 Lecture 16 14 What are “ typical neighborhood gray values”?

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