Question

How to compare two black curves on a white background? How to do it as fast? For example
this

and this

are similar, but this

and this

are not

First curve I’ll draw on JPanel, second is image.

Answer 1

I have an idea. Not sure that it is the best one, but somehow it allows to evaluate the coefficient of similarity of two cruves.

Lets make a matrix for each cruve putting 1 for black pixels and 0 for white ones. Now if we want to compare two cruves with matrixes a and b at first we should construct third matrix c where:

if(a[i][j] == 0 && b[i][j] == 0)
    c[i][j] = 0;
else if(a[i][j] == 0 || b[i][j] == 0)
    c[i][j] = 1;
else
    c[i][j] = 2;

Then we will denote by S count of cells where c[i][j] != 0, and by T count of cells where c[i][j] == 2. And at last two cruves are similar if T / S > 1 - eps, where eps you should choose yourself according what accuracy you want to get.