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Broad-band light sources have a lot of wavelengths in them. We use broad band light sources to estimate ground truth.
Intensity vs mirror position corresponding to all the wavelengths are going to have a maxima when mirror position x is same as d in Figure 1. But the rest of the maximas for each individual wavelengths are going to be misaligned as shown in Figure 2. Figure 2 shows Intensity vs x graph for two wavelengths (out of the many in broadband source)
As a result, for broadband light source, the only maxima is going to be at x=d since that’s where all the maximas coincide.
The rest of the values of x mean some wavelengths will not have a maxima and thus the value is always going to be lesser than at d.
We scan for a lot of values of x for precision and select the x corresponding to a maxima for each of the pixels in the image.
This takes a couple of hours however.