Plot a circle of desired intensity.

I have the following code to draw a white square on a black background. The intensity of the square can be varied from 0 to 256 from black to white.

backg = uint8(zeros(500,500,3));%produce 500x500 px background
for x = 200:1:300; %define x limits of square 
    for y = 200:1:300; %define y limits of square 
    backg(x,y,:) = 256; %choose intensity
    end;
end;
image(backg);

I would like to use the same code to plot a circle, but I get errors related to array indices.

Many thanks.

[darova]

Do you know how to draw a circle?

Answer 1

[Image Analyst]

Code is in the FAQ: https://matlab.fandom.com/wiki/FAQ#How_do_I_create_a_circle.3F

Adapt as needed (center location, radius, intensity, etc.).

[Jose Aroca]

Yeah, I saw that before. However, I want a circle in which the intensity can be varied. I developed this code in which the intensity can be varied according to the radius.

imagelength=100;
middle=(imagelength+1)/2;
radius=20;
dimmerRadius=15;
brightness=256;
dimmerBrightness=150;

image=ones(imagelength);
for i=1:imagelength
    x=-imagelength+middle+i;  %change y coordinate by adding term
    for j=1:imagelength
        y=-imagelength+middle+j; %change x coordinate by adding term
        if(x^2+y^2<=radius^2)  %equation of desired shape
            image(i,j)=brightness;
        end
        if(x^2+y^2<=dimmerRadius^2)
            image(i,j)=dimmerBrightness;
        end
    end
end
imagesc(image)
axis square
axis off
colormap gray
caxis([1 256])

However, I want the intensity to vary as a Gaussian, ie. to be maximum at the centre and tail off as r is increased. Any ideas?

[Image Analyst]

See my attached demo. Adapt as needed.