How to find out amplitude from circular fringes (circular interferogram)

I have circular interferogram fringes and i have to find out the amplitude from this interferogram but unable do that. Please help me me if any body have idea about that. Thanks in advance

Answer 1

[Image Analyst]

Where did you post your image? The dumb obvious way is to just use the max value of the image (assuming the fringes are bright). Other, more sophisticated (robust to noise) ways would be to try to find the fringes and find their center lines, and take the mean intensity of the image along the center line of the fringes, perhaps throwing out any obvious outliers first.

[Akash]

hello Sir Thanks for replying Still i am unable to do that.......can u throw more light on this.....It will be very helpful for me. Circular interferogram are widely available on web.

[Image Analyst]

amplitude = max(yourImage(:));

I see lots of interferograms - why not make it easy for us? Can't you just pick one that looks like your image and tell us what the URL is, or better yet, upload your image to tinypic.com or somewhere? Why make me pick one - I'm sure I'll end up picking one that you will say isn't quite like what you have.

[Akash]

Hello sir Sorry for that. I upload image at.............. http://imageshack.us/content_round.php?page=done&l=img198/4104/vatech.png

[Image Analyst]

I'm sure there must be lots of interferogram fringe finding algorithms out there. In 5 minutes I doubt I'll invent the best one, better than anything out there. Which one are you using? Do you have code for it?

[Akash]

Sir i am using 4-phase shifting algorthim for finding the phase. Its giving correct pahse but amplitude not.

% A=imread('path\I1.bmp); B=imread('path\I1.bmp'); C=imread('path\I1.bmp'); D=imread('path\I1.bmp'); A1=double(A(1:1:542,1:1:810)); B1=double(B(1:1:542,1:1:810)); C1=double(C(1:1:542,1:1:810)); D1=double(D(1:1:542,1:1:810)); psin=D1-B1; pcos=A1-C1; phase=atan2(Pcos./psin); Amplitude=sqrt(psin.^2+pcos.^2);

[Image Analyst]

I don't understand. It looks A, B, C, and D are all the same thing. They all came from reading in I1.bmp.

[Akash]

A,B,C,D are four 90degree phase shifted interferogram respectively. I1(zero degree), I2(90deg) ,I3(180deg) andI4(270degree)

% A=imread('path\I1.bmp); B=imread('path\I2.bmp'); C=imread('path\I3.bmp'); D=imread('path\I4.bmp'); A1=double(A(1:1:542,1:1:810)); B1=double(B(1:1:542,1:1:810)); C1=double(C(1:1:542,1:1:810)); D1=double(D(1:1:542,1:1:810)); psin=D1-B1; pcos=A1-C1; phase=atan2(Pcos./psin); Amplitude=sqrt(psin.^2+pcos.^2);

[Walter Roberson]

http://www.mathworks.com/matlabcentral/answers/13205-tutorial-how-to-format-your-question-with-markup

[Image Analyst]

Do you have a reference for those equations that you used?

[Akash]

It is very famous method for finding the phase. You can find it on at page no 11 of the given URL

http://fp.optics.arizona.edu/jcwyant/Short_Courses/SPIE-7-30-2000/Session%209.pdf

[Image Analyst]

Ah yes. I probably should have remembered that. I actually took this course in person from Jim Wyant but that was 31 years ago. I don't work in interferometry anymore so I guess my memory faded. I still have friends back there in Tucson at the College of Optical Sciences of the University of Arizona - tell Jim I said Hi.

It looks like your A-D the same I1 - I4 in the reference. Is that right? Because it looks like you're asking for the amplitude Iprime which is not used or needed.