curve fitting

[aalim]

deal all

i am new to labview (using labview 8.5), i have a fringe picture of laser interferometer (attached here with). i want curve fitting along the edge of each fringe ( curve fitting  of equal intensity pixel points along each fringe), please help me how can i meet these requirements.

thanks

aalim

[SULLutions]

aalim,

The IMAQ Threshold VI in the NI Vision package will do the job. Set the Range to allow only one pixel value and you can turn all those pixels any shade of gray you'd like.

[altenbach]

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aalim wrote: 

i am new to labview (using labview 8.5), i have a fringe picture of laser interferometer (attached here with). i want curve fitting along the edge of each fringe ( curve fitting  of equal intensity pixel points along each fringe), please help me how can i meet these requirements.

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 Sorry, I am not familiar with your experiment, but what exactly do you want to fit?

Are you trying to fit for the large stripes (with straight lines) or for the small circular patterns??

(For the large stripes, a 2D FFT might be all you need. ;)) 

[aalim]

thank you sir.

can i have an example or coding for how to use imaq.

[SULLutions]

aalim,

The LabVIEW help for IMAQ Threshold (which I found rather confusing itself) refers to two examples. I'd suggest Vision>>2. Functions>>Binary Analysis>>Particle Analysis Report Example.vi. Adjusting the "Threshold Value" sliders will give you a very good idea of how IMAQ Threshold works. In fact, substituting your image for the canned one will probably give you a good visual of what you want (though the particle analysis part won't make any sense).

If you do not have IMAQ Vision installed already, ask your local NI rep for an evaluation license. Mention specifically that you are interested in IMAQ Threshold. (NI keeps changing the terminology of their packages and even the NI reps have trouble telling which vision package is which.)

[aalim]

thank you sir will try it .

[DFGray]

Do you want a display or actual equations for the equal intensity profiles?

If all you want is a display, you can do this rather simply using an intensity graph and a custom color table (set it to standard grayscale with the levels you want in a highlighted color).

If you want equations, you will need to do some work, if all you have is standard LabVIEW.  I have not actually done this, but would probably start with something like:

1. Do 2D FFT to find out phase and period of the fringes (this allows you to localize the data you will be curve fitting), as altenbach suggested.
2. Using the phase and period information, get a subset of your data and find the XY locations of the data which are at the level you wish to fit.
3. Do your function fit to the data subset.
4. Repeat for other available fringes

This will not be a trivial exercise.  Good luck.