x1=imread('d:\1.jpg')
f0=0;g0=0;
f1=70;g1=30;
f2=180;g2=230;
f3=255;g3=255;
figure,plot([f0,f1,f2,f3],[g0,g1,g2,g3])
axis,xlabel('f'),ylabel('g');
title('灰度變換曲線');
r1=(g1-g0)/(f1-f0);
b1=g0-r1*f0;
r2=(g2-g1)/(f2-f1);
r3=(g3-g2)/(f3-f2);
b2=g1-r2*f1;
b3=g2-r3*f2;
[m,n]=size(x1);
x2=double(x1);
for i=1:m
    for j=1:n
        f=x2(i,j);
        g(i,j)=0;
        if(f>=0)&(f<=f1)
            g(i,j)=r1*f+b1;
        elseif(f>=f1)&(f<=f2)
            g(i,j)=r2*f+b2;
        elseif(f>=f2)&(f<=f3)
            g(i,j)=r3*f+b3;
        end
    end
end
figure,subplot(1,2,1),imshow(x1);subplot(1,2,2),imshow(mat2gray(g));