(Adding this in the solution as I can use the layout tags here.)
OK, I see.
In this case I would recommend that you write a function that does linear approximation of parts of the curve (or some other approximation (e.g. quadratic) that you can model reasonably).
The function would look somehow along this line:
double F(double x)
{
double RetCode;
if(x < 0.2) {
RetCode = a1 * x + b1;
} else if (x < 0.6) {
RetCode = a2 * x + b2;
} else if (x < 0.8) {
RetCode = a3 * x + b3;
} else {
RetCode = a4 * x + b4;
}
return RetCode;
}
and find matching rages with the a1, b1, a2, b2, ...
Extracting the values form a hand-drawn pixel image is just not something you should ever reasonably consider.
For example, some columns of your image had more than one pixel, what value would you assign in this case?