draw circle on image

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sangeeta
sangeeta 2013-3-18
评论： Image Analyst 2021-6-22
I want to draw a circle with centre at centre of given image. Image get displayed but circle is missing. Without using hold on/off, a separate figure window shows circle, but i want the circle on the image. Plz correct the following code.
imshow(PICpng);
centx = x / 2;
centy = y / 2;
r = 10;
hold on;
theta = 0 : (2 * pi / 10000) : (2 * pi);
pline_x = r * cos(theta) + centx;
pline_y = r * sin(theta) + centy;
k = ishold;
plot(pline_x, pline_y, '*');
hold off;
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sangeeta
sangeeta 2013-3-21
ok, Thanks Spandan
Image Analyst
Image Analyst 2013-3-21
编辑：Image Analyst 2013-3-21
Spandan, does the help's "See also" connect to other toolboxes? If so, then the help for rectangle(), which people usually use to draw circles, should mention viscircle().

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采纳的回答

Image Analyst
Image Analyst 2013-3-18
It was working. Your x and y were probably messed up. Try this:
PICpng = imread('peppers.png');
[rows columns numberOfColorChannels] = size(PICpng)
x = columns/2
y = rows/2
imshow(PICpng);
centx = x / 2;
centy = y / 2;
r = 60;
hold on;
theta = 0 : (2 * pi / 10000) : (2 * pi);
pline_x = r * cos(theta) + centx;
pline_y = r * sin(theta) + centy;
k = ishold;
plot(pline_x, pline_y, 'r-', 'LineWidth', 3);
hold off;
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Image Analyst
Image Analyst 2021-6-22
Once you have a mask for the inside the red circle (call poly2mask() if you need to), you can do
pixelsInside = binaryImage(circleMask);
if all(pixelsInside)
% All values in mask are true/white/1
else
% At least one pixel is false/black/0.
end

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更多回答（1 个）

Muhammad Nauman Arshad
ICpng = imread('peppers.png');
[rows columns numberOfColorChannels] = size(PICpng)
x = columns/2
y = rows/2
imshow(PICpng);
centx = x / 2;
centy = y / 2;
r = 60;
hold on;
theta = 0 : (2 * pi / 10000) : (2 * pi);
pline_x = r * cos(theta) + centx;
pline_y = r * sin(theta) + centy;
k = ishold;
plot(pline_x, pline_y, 'r-', 'LineWidth', 3);
hold off;

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