Display images in interferogram (phase variation) mode

#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