matlab練習程序（透視變換）

close all;
clc;
H=1;                        %索引pix中第一個元素，即高度
W=2;                        %索引pix中第二個元素，即寬度
left_right=0.3;               %抬起左邊或右邊時值為0-1之間，不抬起時為0
up_down=0;                %抬起上邊或下邊時值為0-1之間，不抬起時為0

img=imread('lena.jpg');       %這里v為原圖像的高度，u為原圖像的寬度
imshow(img);                    %這里y為變換后圖像的高度，x為變換后圖像的寬度
%img=flipud(img);           %注釋掉為抬起下邊，沒注釋掉為抬起上邊
%img=fliplr(img);           %注釋掉為抬起右邊，沒注釋掉為抬起左邊
[v u]=size(img);


a=1;b=up_down;c=0;
d=left_right;e=1;f=0;
g=up_down/v;h=left_right/u;i=1;
rot=[a b c;d e f;g h i];

pix1=[1 1 1]*rot./(g+h+i);                 %變換后圖像左上點的坐標
pix2=[1 u 1]*rot./(g*v+h+i);               %變換后圖像右上點的坐標
pix3=[v 1 1]*rot./(g+h*u+i);               %變換后圖像左下點的坐標
pix4=[v u 1]*rot./(g*v+h*u+i);             %變換后圖像右下點的坐標

height=round(max([abs(pix1(H)-pix3(H))+0.5 abs(pix2(H)-pix3(H))+0.5 ...
                  abs(pix1(H)-pix4(H))+0.5 abs(pix2(H)-pix4(H))+0.5]));     %變換后圖像的高度

width=round(max([abs(pix1(W)-pix2(W))+0.5 abs(pix3(W)-pix2(W))+0.5 ...
                 abs(pix1(W)-pix4(W))+0.5 abs(pix3(W)-pix4(W))+0.5]));      %變換后圖像的寬度
imgn=zeros(height,width);

delta_y=abs(min([pix1(H)-0.5 pix2(H)-0.5 pix3(H)-0.5 pix4(H)-0.5]));            %取得y方向的負軸超出的偏移量
delta_x=abs(min([pix1(W)-0.5 pix2(W)-0.5 pix3(W)-0.5 pix4(W)-0.5]));            %取得x方向的負軸超出的偏移量

for y=1-floor(delta_y):height-floor(delta_y)
    for x=1-floor(delta_x):width-floor(delta_x)
        pix=[y x 1]/rot*(g*y+h*x+i);                                %用變換后圖像的點的坐標去尋找原圖像點的坐標，                                         
                                                            %否則有些變換后的圖像的像素點無法完全填充
        if pix(H)>=0.5 && pix(W)>=0.5 && pix(H)<=v && pix(W)<=u
            imgn(y+floor(delta_y),x+floor(delta_x))=img(round(pix(H)),round(pix(W)));
        end   
        
    end
end
figure,imshow(uint8(imgn));

%%二次變換,暫時只想起來這種笨方法，一次變換好像沒法進行透視變換
img=imgn;
[v u]=size(img);
a=1;b=-b/2;c=0;
d=-d/2;e=1;f=0;
g=0;h=0;i=1;
rot=[a b c;d e f;g h i];

pix1=[1 1 1]*rot./(g+h+i);                 %變換后圖像左上點的坐標
pix2=[1 u 1]*rot./(g*v+h+i);               %變換后圖像右上點的坐標
pix3=[v 1 1]*rot./(g+h*u+i);               %變換后圖像左下點的坐標
pix4=[v u 1]*rot./(g*v+h*u+i);             %變換后圖像右下點的坐標

height=round(max([abs(pix1(H)-pix3(H))+0.5 abs(pix2(H)-pix3(H))+0.5 ...
                  abs(pix1(H)-pix4(H))+0.5 abs(pix2(H)-pix4(H))+0.5]));     %變換后圖像的高度

width=round(max([abs(pix1(W)-pix2(W))+0.5 abs(pix3(W)-pix2(W))+0.5 ...
                 abs(pix1(W)-pix4(W))+0.5 abs(pix3(W)-pix4(W))+0.5]));      %變換后圖像的寬度
imgn=zeros(height,width);

delta_y=abs(min([pix1(H)-0.5 pix2(H)-0.5 pix3(H)-0.5 pix4(H)-0.5]));            %取得y方向的負軸超出的偏移量
delta_x=abs(min([pix1(W)-0.5 pix2(W)-0.5 pix3(W)-0.5 pix4(W)-0.5]));            %取得x方向的負軸超出的偏移量

for y=1-floor(delta_y):height-floor(delta_y)
    for x=1-floor(delta_x):width-floor(delta_x)
        pix=[y x 1]/rot*(g*y+h*x+i);                                %用變換后圖像的點的坐標去尋找原圖像點的坐標，                                         
                                                            %否則有些變換后的圖像的像素點無法完全填充
        if pix(H)>=0.5 && pix(W)>=0.5 && pix(H)<=v && pix(W)<=u
            imgn(y+floor(delta_y),x+floor(delta_x))=img(round(pix(H)),round(pix(W)));
        end   
        
    end
end
%imgn=flipud(imgn);             %注釋掉為抬起下邊，沒注釋掉為抬起上邊
%imgn=fliplr(imgn);             %注釋掉為抬起右邊，沒注釋掉為抬起左邊
figure,imshow(uint8(imgn));     

圖片福利：

注：更好的實現在這里

參考網址：

1.http://homepages.inf.ed.ac.uk/rbf/CVonline/LOCAL_COPIES/EPSRC_SSAZ/epsrc_ssaz.html

2.http://alumni.media.mit.edu/~cwren/interpolator/

3.http://www.robots.ox.ac.uk/~vgg/presentations/bmvc97/criminispaper/