How to select best x-axis values correspond to curve knee y-axis values

I'm plotting this curves shown below, and I want to extract the best x-axis values correspond to curve knee y-axis values. My target is , for each curve, to pick the smallest x-axis value where the y-axis values seem to start to flatten out.

see this figure.

Answer 1

[KSSV]

Try fitting a striaght line for the requrired points using polyfit and check for devaitaion of points from the line and pick the required points.

[Mohsen Ali]

Could you please support with matlab code?

[KSSV]

Provide data and specify your region points manually....

[Mohsen Ali]

Oh,

I did this manually, I want to do it dynamically such that we can pick the smallest X value for each curve at the position the curve starts to be flatten out.

Could you help me according to my figure above?