How to judge a point whether inside a closed contour or not?

Assume a circle contour image matrix

 c= [ 0 0 0 0 1 0 0 0 0
      0 0 0 1 0 1 0 0 0
      0 0 1 0 0 0 1 0 0
      0 1 0 0 0 0 0 1 0
      0 1 0 0 0 0 0 1 0
      0 0 1 0 0 0 1 0 0
      0 0 0 1 0 1 0 0 0
      0 0 0 0 1 0 0 0 0 ]

and a point p=[4 3], apparently inside this circle. But, how to make such judgement in matlab.

Answer 1

[Walter Roberson]

http://www.mathworks.com/help/images/ref/imfill.html imfill ('holes'). If the point gets assigned a non-zero value then it is inside a closed contour.

[Image Analyst]

Clever. If you want to know if it's on the perimeter or inside (not on perimeter) then check c first

if c(4,3)
  % On perimeter.
else
  filledc = imfill(c, 'holes');
  if filledc(4,3)
    % Inside, not on perimeter
  else
    % Not inside any closed contour at all
  end
end

If you don't care whether it's on the perimeter or inside, just do

filledc = imfill(c, 'holes');
if filledc(4,3)
    % Inside, or on perimeter
else
    % Not inside any closed contour at all
end

[John W. Z]

Cheers~