what is code for non-maxima suppression of a grey image

Edge detection using wavelet transform need local maxima to find new approximation coefficient from detail coefficient.

Answer 1

[Sajid Khan]

Hi, attached is the source code for non maximal suppression. I also have submitted the code in file exchange but it will take some time for approval. I got help from canny edge detection code given in image processing toolbox

[S. Sal]

Hello Sajid Khan, I am getting this error while using nonMaximalSupp.m you shared, The error is as follows: ___________________________________________________________

Undefined function 'cannyFindLocalMaxima' for input arguments of type 'double'.

Error in nonMaximalSupp (line 19) idxLocalMax = cannyFindLocalMaxima(dir,dx,dy,magGrad); _________________________________________________

Can you refine it please ? Thanks

[Swank Williams]

Hi @S. Sal, for the function cannyFindLocalMaxima, you may have a try on the following codes. And you can find more details in the link https://www.cnblogs.com/mender/p/3501929.html

function idxLocalMax = cannyFindLocalMaxima(direction,ix,iy,mag)
[m,n] = size(mag);
switch direction
 case 1
  idx = find((iy<=0 & ix>-iy)  | (iy>=0 & ix<-iy));
 case 2
  idx = find((ix>0 & -iy>=ix)  | (ix<0 & -iy<=ix));
 case 3
  idx = find((ix<=0 & ix>iy) | (ix>=0 & ix<iy));
 case 4
  idx = find((iy<0 & ix<=iy) | (iy>0 & ix>=iy));
end

if ~isempty(idx)
  v = mod(idx,m);
  extIdx = (v==1 | v==0 | idx<=m | (idx>(n-1)*m));
  idx(extIdx) = [];
end
 
ixv = ix(idx);  
iyv = iy(idx);   
gradmag = mag(idx);


switch direction
 case 1
  d = abs(iyv./ixv);
  gradmag1 = mag(idx+m).*(1-d) + mag(idx+m-1).*d; 
  gradmag2 = mag(idx-m).*(1-d) + mag(idx-m+1).*d; 
 case 2
  d = abs(ixv./iyv);
  gradmag1 = mag(idx-1).*(1-d) + mag(idx+m-1).*d; 
  gradmag2 = mag(idx+1).*(1-d) + mag(idx-m+1).*d; 
 case 3
  d = abs(ixv./iyv);
  gradmag1 = mag(idx-1).*(1-d) + mag(idx-m-1).*d; 
  gradmag2 = mag(idx+1).*(1-d) + mag(idx+m+1).*d; 
 case 4
  d = abs(iyv./ixv);
  gradmag1 = mag(idx-m).*(1-d) + mag(idx-m-1).*d; 
  gradmag2 = mag(idx+m).*(1-d) + mag(idx+m+1).*d; 
end
idxLocalMax = idx(gradmag>=gradmag1 & gradmag>=gradmag2); 

Answer 2

[Image Analyst]

Sounds like you have a paper in mind. Did you ask the authors if they have code to share with you, or search the File Exchange? I don't have the wavelet toolbox so I can't help you.

Answer 3

[Image Analyst]

Try the function imhmax() built in to the Image Processing Toolbox.