Draw a gradient circle within a circle
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I want to code a gradient circle within a circle like shown in the diagram. Any help will be appreciated. 
采纳的回答
One way might be to use a patch with vertex interpolation, as in this example.
EDIT:
Here's how you might apply that to a circle:
t=linspace(0,360,500); t(end)=[];
x=cosd(t);
y=sind(t);
c=cosd(t);
patch(x,y,c); colormap(gray); axis equal; caxis([-0.7970 ,0.6373])
15 个评论
Sajjad Ahmad Khan
2021-6-19
Matt J
2021-6-19
You should see an example there with a gradient transition across triangles, similar to what you are trying to do with circles.
Scott MacKenzie
2021-6-19
编辑：Scott MacKenzie
2021-6-19
@Matt J I tried -- without success -- to extend this example to circles. I think it's tricky because a circle doesn't have faces and vertices. When I tried to concoct a circle as a many-sided polygon, the color interpolation seemed to go a bit wonky:
@Scott MacKenzie See my edited answer
Scott MacKenzie
2021-6-19
@Matt JWow, excellent. Thanks for this
Hi Matt, I want to add the gradient circle that you plotted inside the white circle in the following code. How can I do that?
% First create the image.
imageSizeX = 256;
imageSizeY = 256;
image=zeros(imageSizeX,imageSizeY);
[columnsInImage rowsInImage] = meshgrid(1:imageSizeX, 1:imageSizeY);
% Next create the circle in the image.
centerX = 128;
centerY = 128;
radius = 100;
circlePixels = (rowsInImage - centerY).^2 ...
+ (columnsInImage - centerX).^2 <= radius.^2;
% circlePixels is a 2D "logical" array.
% Now, display it.
image(circlePixels)=256;
imshow(image, [])
Doing this with images is much easier than with plots...
gradientCircle=columnsInImage.*circlePixels;
gradientCircle(circlePixels)=rescale(gradientCircle(circlePixels),0,255);
imshow(gradientCircle, [])
Sajjad Ahmad Khan
2021-6-19
Well, it's very easy to add a circle around the first.
halo=imdilate(circlePixels,strel('disk',10)) & ~circlePixels;
gradientCircle(halo)=255;
imshow(gradientCircle, []);shg
Sajjad Ahmad Khan
2021-6-19
@Matt J Thanks for your reply. This function is really helpful but I want to code such that I could change the dimensions of image and inner circles. I want some like this shown image. How can I modify my above mentioned code to get something like this image? Thanks
Matt J
2021-6-19
Well, the radius is a parameter you do control, isn't it? You set it to 100 in your original code, but you could easily change it to something else.
Sajjad Ahmad Khan
2021-6-20
Matt J
2021-6-20
The inner circle is the one that you coded. The outer circle is coded by choosing the strel radius in strel('disk',10)
Sajjad Ahmad Khan
2021-6-20
Matt J
2021-6-20
You're quite welcome, but please Accept-click the answer if you consider the question resolved.
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