How to measure destance between a line's points and a spacific point

Hello, i am looking for a way to find the distance between A and the (B,C)edge. for example, if i have 50 pixels on (B,C)edge then it should returen 50 distance value. (the main problem is in defining (B,C)edge without taking other boundaries like (A,B) or (A,C)).

[Cedric]

Can you assume that the edge BC is always defined by the first black pixel (vertically, in the downward direction) after which all pixels are black? If so, a basic FIND will identify the edge (using the 'last' option), and computing distances from row/col indices (using differences with row/col of point A) is trivial.

[KALYAN ACHARJYA]

What you want exactly? The distance between A and B?? And Distance between A & B? Clarify the problem.