Draw a gradient circle within a circle

I want to code a gradient circle within a circle like shown in the diagram. Any help will be appreciated.

Answer 1

[Matt J]

One way might be to use a patch with vertex interpolation, as in this example.

https://www.mathworks.com/help/matlab/ref/patch.html#buscm5g-1

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])

[Sajjad Ahmad Khan]

I haven't found answer from the shared link

[Matt J]

You should see an example there with a gradient transition across triangles, similar to what you are trying to do with circles.

[Scott MacKenzie]

@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:

[Matt J]

@Scott MacKenzie See my edited answer

[Scott MacKenzie]

@Matt JWow, excellent. Thanks for this

[Sajjad Ahmad Khan]

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, [])

[Matt J]

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]

I actually want an image of zeros of some height and width in which I have two circles, the outer circle should be white and inner most circle should have a gradient (0 to 255). See the first image that I had posted in a question. Thanks

[Matt J]

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]

@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]

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]

@Matt J yes I can control the radius of outer circle but how to control the radius of inner circle that you coded? Thank you!

[Matt J]

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]

@Matt J Thank you so much. I appreciate your help!

[Matt J]

You're quite welcome, but please Accept-click the answer if you consider the question resolved.