| poledetection - poles (or residues) detection in a wrapped phased image |
poles = poledetection(image[,threshold]) |
| image |
| The gray-level image containing the wrapped phase. |
| threshold |
| The minimum difference betwwen 2 pixels to consider that a phase jump occurs. Default=0.5 |
| poles |
| A matrix: elements with the value zero are consistent points, others (positive or negative) are residus (or poles). |
|
Ideally, phase unwrapping should not depend on the path
followed to unwrapp. So we consider a small loop of 4
adjacents pixels. We decide that there's a phase jump if the
difference between 2 neighbours is superior to a threshold
(=0.5 by default) We count the number of jumps when we
follow the loop clockwise and anticlockwise. Because of
noise, we observe that these numbers are differents in
certain locations of the image. The phase is called
"inconsistent" in these points. Unwrapping process
is very uncertain there. These poles (or residues) can be marked so that the unwrapping process ignores them, or can be used to create branches in residue-cut tree algorithms. |
stacksize(4e7);
pw=gray_imread(SIPDIR+'images/photonics/pyramide_noisy.jpg'); //phase wrapped
xset("window",0);xbasc();imshow(pw);
poles=abs(poledetection(pw));//locate residues, no matter of the sign
xset("window",1);xbasc();imshow(poles,[]);//bright pixels
// show places where phase jumps are very uncertains
//Avoid unwrapping these points:
mf=imvariance(pw);//calculate a "merit function"
//mark bad pixels as visited (merit function=3000):
//you can comment this line if you want to compare results with and without
//poledetection
mf(find(poles>0))=3000;
//phase unwrapping:
puw=unwrapp(pw,mf);
xset("window",2);xbasc();imshow(puw,[]);
|
| Phase unwrapping algorithms for radar interferometry: residue-cut, least-squares, and synthesis algorithms by Zebker and Lu, Journal of Optical Society Am. A, vol 15, N.3, March 1998 |
| Satellite radar interferometry: two-dimensional phase unwrapping by Goldstein, Zebker, Werner in Radio Science, vol 23, number 4, pages 713-720, july-august 1988 |
| Jocelyn DRUEL <jocelyn.druel1@libertysurf.fr> |
| The latest version of the Scilab Image Processing toolbox can be found at |
| http://siptoolbox.sourceforge.net |
| unwrapl, unwrapp, imvariance |