clear?all
clc

t=clock;?%back?project直接反投影
I=phantom（256）;%?Ein??Shepp-logan?Bild?begruenden
%I=imread（‘lena_8.bmp‘）;
II=double（I）;
[iLength?iWidth]?=?size（II）;
ISize=?sqrt（iLength^2?+?iWidth^2）;%找對角線長度，即最大長度
LengthPad?=?ceil（ISize?-?iLength）?+?2;
WidthPad?=?ceil（ISize?-?iWidth）?+?2;
padIMG?=?zeros（iLength+LengthPad?iWidth+WidthPad）;
padIMG（ceil（LengthPad/2）:（ceil（LengthPad/2）+iLength-1）...
????ceil（WidthPad/2）?:?（ceil（WidthPad/2）+iWidth-1）?）=?II;
theta=0:179;
m=?length（theta）;
PR?=?zeros（size（padIMG2）?m）;
for?i?=?1:m
???tmpimg?=?imrotate（padIMG?90-theta（i）?‘bilinear‘?‘crop‘）;
???%?imrotate:?圖像；角度；
???%內插方式：the?output?pixel?value?is?a?weighted?average?of?pixels?in?the?nearest?2-by-2?neighborhood
???%Data?Types:?Make?output?image?B?the?same?size?as?the?input?image?A?cropping?the?rotated?image?t