Es gibt einige Möglichkeiten, dies zu erreichen. Eine Möglichkeit, die Maske vor (oder regionprops
) so zu ändern, dass sie nur enthält Pixel, die innerhalb des angegebenen Kreises sind. In diesem Beispiel wird davon ausgegangen, dass Sie bereits über eine logische Matrix M
verfügen, die Sie an übergeben.
function [A, boundaries] = traceWithinCircle(M, x1, y1, R);
%// Get pixel centers
[x,y] = meshgrid(1:size(M, 1), 1:size(M, 2));
%// Compute their distance from x1, y1
distances = sqrt(sum(bsxfun(@minus, [x(:), y(:)], [x1, y1]).^2, 2));
%// Determine which are inside of the circle with radius R
isInside = distances <= R;
%// Set the values outside of this circle in M to zero
%// This will ensure that they are not detected in bwboundaries
M(~isInside) = 0;
%// Now perform bwboundaries on things that are
%// inside the circle AND were 1 in M
boundaries = bwboundaries(M);
%// You can, however, get the area by simply counting the number of 1s in M
A = sum(M(:));
%// Of if you really want to use regionprops on M
%// props = regionprops(M);
%// otherArea = sum([props.Area]);
end
Und als Beispiel
%// Load some example data
data = load('mri');
M = data.D(:,:,12) > 60;
%// Trace the boundaries using the method described above
B = traceWithinCircle(M, 70, 90, 50);
%// Display the results
figure;
hax = axes();
him = imagesc(M, 'Parent', hax);
hold(hax, 'on');
colormap gray
axis(hax, 'image');
%// Plot the reference circle
t = linspace(0, 2*pi, 100);
plot(x1 + cos(t)*R, y1 + sin(t)*R);
%// Plot the segmented boundaries
B = bwboundaries(M);
for k = 1:numel(B)
plot(B{k}(:,2), B{k}(:,1), 'r');
end
und was ist dein Problem? – Piglet