coins.png how to find the smallest coin in a image and display it alone in a separate window?

how to find the smallest coin in the image below and display it alone in a separate window

Answer 1

[DGM]

Something like this:

A = imread('coins.png');
m = bwareaopen(A>80,100);

% get areas, sort, get bounding box
C = regionprops(m,'area','boundingbox');
area = vertcat(C.Area);
[~,idx] = min(area);
bbox = C(idx).BoundingBox;

% get subimage, display
thiscoin = imcrop(A,bbox);
imshow(thiscoin)

I chose to interpret "smallest" as meaning "has the least area". If you wanted some measure of diameter, you'd have to get the appropriate region property and sort it.