My work is focused on the study of near field diffraction of gratings. I have recorded images of fringe patterns found after the gratings with a CCD camera and I would like to measure the contrast or visibility of the fringes.
If you open your images in some analysis software such as ImageJ, you can read the intensity of the image and use this to work out the contrast.
In ImageJ you could measure the intensity along a line, and plot this to see if the fringe pattern is what you expect.
Fringe visibility (m) is calculated as:
m = (Imax-Imin)/(Imax+Imin)
Where Imax and Imin are the maximum and minimum intensities within the fringe pattern.
Or you can use
visibility = amplitude/average
where average of the fringes is the sum of the intensities (or powers) of the two interfering waves
Thanks, but for arbitraty periodical light distribution the method mentioned by Alexander is not applicable.
probably, methods based on the fitting of the histogram or grayscale profile are more suitable.
As I said in my first answer, you can easily deduce the fringe profile using software like ImageJ, which is open source.
I did this for a particularly poor image of a fringe pattern found on the internet and the result is attached. This data could then be exported and analysed in a software of your choosing, where you could then plot an appropriate fit, whether it be a sinc function, cos function with a sinc envelope or whatever depending on what type of grating you are using.
Yes, thanks. I know imageJ and how to create profiles.
but I am looking for histogram or variogram-based methods.
Is this the sort of thing you are after?
http://eprints.ucm.es/23169/1/QuirogaJA81.pdf
yes, something like that !!
This is one method. But, I think that the method based in histogram of the iimage are better for my experiments. Exactly the method described in reference [3] in that paper. But I cannot download that reference.
See some details about processing of digital interferograms with a support of OroginLab soft in the paper attached my RG.
Article Precision measurement and determinations of laser radiation ...
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