clc;
clear all;
X1=imread('elain.bmp');
subplot(121),imshow(X1);
f0=0;g0=0;
f1=20;g1=10;
f2=100;g2=130;
f3=255;g3=255;
r1=(g1-g0)/(f1-f0);
b1=g0-r1*f0;
r2=(g2-g1)/(f2-f1);
b2=g1-r2*f1;
r3=(g3-g2)/(f3-f2);
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>=f1)&(f<=f2)
            g(i,j)=r1*f+b2;
        elseif(f>=f2)&(f<=f3)
            g(i,j)=r3*f+b3;
        end
    end
end
subplot(122),imshow(mat2gray(g))