p=phantom（256）;
imtool（p[]）;
[m?n]=size（p）;
x0=m/2;
y0=n/2;
radius=sqrt（x0^2+y0^2）;
for?x=1:m
????for?y=1:n
????????if?（x-x0）^2+（y-y0）^2>=2025?&&?（x-x0）^2+（y-y0）^2<=2500
????????????p（xy）=0.5;
????????end
????end
end?
imtool（p[]）;???%加環形偽影
BW1=edge（p‘sobel‘0.01）;?%sobel圖像邊緣提取
imtool（BW1[]）;
tt=zeros（360181）;
for?theta=1:360
????for?r=1:181
????????i=x0+round（r*cos（theta/180*pi））;
????????j=y0+round（r*sin（theta/180*pi））;
????????if??i>=1?&&?i<=m?&&?j>=1?&&?j<=n
???????????tt（thetar）=BW1（ij）;
????????end
????en