second derivate of an histogram

Hi!

I'm plotting an area of an image that each day (represented by #fx) gets darker. The values are normalised by a white region, that is why the values varies from 0 to 1 (first image).

As you can see in the first image (3fx), there are two peaks between 0.7 and 0.8. And then along time, the smallest peak becomes bigger.

I want to measure how much does the peaks moves from on day to another. I found an option to plot the histogram as a curve using 'ksdensity',as you can see in the second image for 3 different days.

How can I transform that curve to a function so I can calculate the second derivate, to see the peaks of each day and quantify how much do they translate along time?

Answer 1

[Star Strider]

I am not sure what you want.

You can use the gradient (link) function to take the numerical derivative, and use it a second time (or the related del2 (link) function) to take the second derivative.

If you only want to locate the peak amplitudes and their positions, I would use the Signal Processing Toolbox findpeaks (link) function.