Create Rainbow using matlab

Last night I was watching dragon tales, a cartoon series. I saw a scene with rainbow and my mind started to think to implement that rainbow in MATLAB. To my surprise, what I learned in the tenth grade mathematics came in handy, the equation of a circle.  Many times our lower class basic mathematics will come throughout our life. As a result I have started to read tenth grade mathematics once again ;-)

I followed the same procedure, 'How to draw a circle'. Instead of finding the midpoint for x co-ordinate I took the image size, so that I may get a half a circle.

sz=400;

rad=200;

clear RGB

RGB(1:sz,1:sz,1:3)=255;

RGB=uint8(RGB);

[x y z]= find(RGB==255);

xc=sz;

yc=ceil((sz+1)/2);

for i=1:12

    radius=(rad-10*i).^2;

    r=find(((x-xc).^2+(y-yc).^2)<=radius);

   

for j=1:size(r,1)

    if(mod(i,2)==0)

                RGB(x(r(j)),y(r(j)),:)=255;

    end

            if(mod(i,3)==1)

               RGB(x(r(j)),y(r(j)),:)=0;

            end

        

end

end

B=rgb2gray(RGB);

D=edge(B);

SE=strel('disk',2);

D1=~imdilate(D,SE);

I colored the image based on label

[BW ,L]=bwlabel(D1,8);

    mycolor(:,1)=[128;128;255];

    mycolor(:,2)=[215;0;0];

    mycolor(:,3)=[255;128;0];

    mycolor(:,4)=[255;255;0];

    mycolor(:,5)=[0;128;64];

    mycolor(:,6)=[10;160;220];

    mycolor(:,7)=[0;0;70];

    mycolor(:,8)=[65;0;128];

    mycolor(:,9)=[128;128;255];

for n=1:9

[r c]=find(BW==n);

for i=1:size(r,1)

            RGB(r(i,1),c(i,1),:)=mycolor(:,n);

end

end

imshow(RGB);