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Display images in interferogram (phase variation) mode

s.r.chinn

Fri, 03/09/2012 - 07:58 am

The ModifyImage operation includes a lookup wave option allowing the use of a non-linear color mapping. It occurred to me that this might be a very simple way to display surface heights or phase changes in a manner similar to that created by optical interferometers. All one has to do is make the appropriate sinusoidal lookup wave, and match it to the desired scale. In the example provided, the amplitude of the image wave is measured in wavelengths. For other units, you will have to alter the scaling. The displayed image somehat resembles a conventional contour plot, but has some phase/sign ambiguity. It used an input amplitude of 5.25 .

#pragma rtGlobals=1     // Use modern global access method.
//  best to try this in a new Igor experiment
 
function MakeAndShowTestImage(a)
    variable a  //  wave peak amplitude in this example, in wavelengths
    
    make/O/N=(200,200) w2D
    setscale x, -1, 1,"" w2D
    setscale y, -1, 1,"" w2D
// insert (replace) your definition of w2D here:
// height of w2D is measured in wavelengths
    w2D  = a*(exp(-(((x-0.5)/0.4)^2 + (y/0.4)^2)) - exp(-(((x+0.5)/0.4)^2 + (y/0.4)^2)))
    
    DoWindow Graph0
    if(!V_flag) //  if Graph0 doesn't exist, create it with new image
        newimage w2D
        ModifyGraph height={Plan,1,left,top}
    endif
    MakeNonLinearColorFunc(w2D) //  make the lookup wave
    ModifyImage/W=Graph0 w2D ctab= {*,*,Grays256,0},  lookup = wNL
end
//-------------------------------------------------------------------------------------------------------
function MakeNonLinearColorFunc(inwave) 
// make a nonlinear image LOOKUP wave to simulate interference fringes
    wave inwave //  the 2D image wave to be shown as an interferogram
    
    make/O/N=500 wNL
    variable xmin = waveMin(inwave), xmax = waveMax(inwave)
    setscale/I x, xmin, xmax,"" wNL
    wNL = (cos(2*pi*(xmax-x)))^2    //  set brightest color at maximum of image
end