Find external contour in image Matlab

Hi everyone,

I have the following problem in Matlab: I have the following BW image and I would like to find and separate the external contour of it (I've marked it in red).

This is what I expect to have as final result.

How can I obtain it? Thank you

Answer 1

[darova]

Simple?

[Marco Solbiati]

I want to do it automatically using image processing toolbox.

[darova]

I = imread('image.png');
RGB = [255 0 0];
I1 = I(I(:,1)==RGB(1),I(:,2)==RGB(2),I(:,3)==RGB(3));    % your new image