How can I draw a filled circle?
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vatankhah
il 13 Set 2013
Commentato: Image Analyst
il 21 Giu 2023
I know the radius and the center coordinate of a circle
I want to fill this circle with black color
how can I do this?
3 Commenti
Risposta accettata
Walter Roberson
il 13 Set 2013
5 Commenti
Will Reeves
il 15 Feb 2022
Yes please.. + 1 for that request. please implement "FaceColor" for a viscircles property! I need to draw thousands of circles in a plot...
Will Reeves
il 21 Giu 2023
Also, just for completness.. Is there a "quality setting" somewhere for rectangle (when curvature=1) that draws a circle instead of a load of straight lines?
for example:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1416039/image.jpeg)
Più risposte (7)
Shahriar
il 9 Nov 2013
Very simple. The following will draw a filled circle at (1,1) with red color. Change it as you wish.
plot(1, 1, '.r', 'MarkerSize',69)
5 Commenti
Image Analyst
il 6 Ott 2022
@Sathish Kumar and @Patriek Bruurs, that's correct. The marker size is relative to your screen or figure size or something. It is not relative to the scale used for your x and y axes. So zooming in and out will probably not change the marker size, and the marker size has nothing at all to do with the spatial calibration scale of your x and y. So for example if you wanted a big spot you'd use a markersize of, say, 100 regardless if your x and y axes went from 0-1 or from 0 to a billion. The marker size is NOT the diameter of the spot in units of your graph. So if your axis went from 0 to a billion you'd still use a marker size of 100, not a marker size of 30 million. Also zooming in or out of the axes does not change the marker size - you can imagine scenarios where if it did, it would be a disaster, with the marker covering up some small region you wanted to scrutinize.
Walter Roberson
il 7 Ott 2022
I did some measurements on my screen last night. To within measurement error, the spot size produced by plot() grew linearly -- for example spot size 1000 was twice as large as spot size 500. But I was not able to figure out what the units were; the units did not make sense in inches or mm or points. For example marker size 1000 was approximately 66.4 mm diameter -- between 66.1 and 66.8 (I cannot get my digital calipers flat on the screen and it is a judgement call about where exactly the bounds are.) (Admittedly, due to measurement error, it just might be the case that the spot size is slightly nonlinear.)
My display is a larger one, but is below the bounds at which MATLAB starts lying about resolutions
Image Analyst
il 13 Set 2013
To create a 2D logical image of a solid circle (a disc), you can use code like this:
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = 640;
imageSizeY = 480;
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = 320;
centerY = 240;
radius = 100;
circlePixels = (rowsInImage - centerY).^2 ...
+ (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
image(circlePixels) ;
colormap([0 0 0; 1 1 1]);
title('Binary image of a circle');
10 Commenti
Sharne Fernandes
il 21 Ago 2022
@Image Analyst, could you suggest to me a way of adding more than 1 circles using these steps?
Thank you
Walter Roberson
il 23 Ago 2022
% Create a logical image of a circle with specified
% diameter, center, and image size.
% First create the image.
imageSizeX = 640;
imageSizeY = 480;
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = [100 180 300];
centerY = [150 30 400];
radius = [100 20 50];
circlePixels = any((rowsInImage(:) - centerY).^2 ...
+ (columnsInImage(:) - centerX).^2 <= radius.^2, 2);
circlePixels = reshape(circlePixels, imageSizeY, imageSizeX);
% circlePixels is a 2D "logical" array.
% Now, display it.
image(circlePixels) ;
colormap([0 0 0; 1 1 1]);
hold on
scatter(centerX, centerY, 'r+');
hold off
title('Binary image of circles');
Chad Greene
il 20 Nov 2014
circles(x,y,radius,'color','black')
2 Commenti
Image Analyst
il 6 Feb 2021
Now there is a viscircles function built in to the Image Processing Toolbox
viscircles([x, y], radius);
This can handle vectors of centers and radii, in addition to just one.
ABDULRAHMAN HAJE KARIM ALNAJAR
il 8 Ago 2018
Modificato: Walter Roberson
il 10 Nov 2019
Simply, use the following command:
I = insertShape(I,'FilledCircle',[x y r],'color',[1 1 1],'LineWidth',5);
[x y] is the centre coordinates r is the radius
Note, you need Computer Vision Toolbox to run this command.
1 Commento
Walter Roberson
il 10 Nov 2019
This is a good routine to use if you have a matrix that you want to draw a circle into. It is not, however, a good routine to draw a circle on the display.
vatankhah
il 13 Set 2013
Modificato: vatankhah
il 13 Set 2013
3 Commenti
Will Reeves
il 21 Giu 2023
Modificato: Will Reeves
il 21 Giu 2023
... but it seems as if this is fairly course angular resolution and are therefore not really circles. Please can this adjusted in a future release so that you can chose the angular precision?
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/1416054/image.jpeg)
Image Analyst
il 21 Giu 2023
@Will Reeves remember we're dealing with digital computers that use discrete values and don't have infinite precision. If you're really going to zoom way, way in, so much so that the circle has "kinks" in it because it's made up as very short line segments, you can make those line segments as small as you want by increasing the angular resolution in the code in the FAQ:
Anton
il 24 Set 2014
Modificato: Walter Roberson
il 10 Nov 2019
Use "area" command. Typically used to fill area under y=f(x) curve.
Using Rectangle command has 2 inconveniences: 1) They use figure axes, not the graph axes (see this submission for help http://www.mathworks.co.uk/matlabcentral/fileexchange/30347-sigplot/content/sigplot/sigplot/BasicFunctions/dsxy2figxy.m )
2) a consequence of 1 in fact: if you zoom or move the graph your circle will remain in "old" position and scale, which is annoying.
This is how you draw a filled circle of radius R at (x,y) in the axis of your graph using "area" command:
Ang = 0:0.01:2*pi; %angle from 0 to 2pi with increment of 0.01 rad. CircX=R*cos(Ang); CircY=R*sin(Ang);
h=area(X+CircX,Y+CircY);
set(h,'FaceColor',[.7 0 0]) %colour of your circle in RGB, [0 0 0] black; [1 1 1] white set(h,'LineStyle','none')
% unfortunately you have to remove the line: because circle is not a function strictly speaking. % "area" command tries to fill area below your function which leaves a line-artefact connecting your circle with X axis.
1 Commento
Walter Roberson
il 10 Nov 2019
? rectangle() uses data units, which are axes relative. It does not use figure units.
annotation() uses figure units though.
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