clear all 
close all  
dx=0.01; 
x=-1:dx:1; 
u=255; 
A=87.6;  
% u Law 
yu=sign(x).*log(1+u*abs(x))/log(1+u); 
% A Law for i=1:length(x)     
if abs(x(i))<1/A         
ya(i)=A*x(i)/(1+log(A));     
else         
ya(i)=sign(x(i))*(1+log(A*abs(x(i))))/(1+log(A));     
end 
end  
figure(1) 
plot(x,yu,'k.:') 
title('u Law') 
xlabel('x') 
ylabel('y') 
grid on 
hold on 
xx=[-1,-127/255,-63/255,-31/255,-15/255,-7/255,-3/255,-1/255,...     1/255,3/255,7/255,15/255,31/255,63/255,172/255,1]; 
yy=[-1,-7/8,-6/8,-5/8,-4/8,-3/8,-2/8,-1/8,1/8,2/8,3/8,4/8,5/8,6/8,7/8,1]; 
plot(xx,yy,'r') 
stem(xx,yy,'b-.') 
legend('u律壓縮特性','折線近似u律')  
figure(2) 
plot(x,ya,'k.:') 
title('A Law') 
xlabel('x') 
ylabel('y') 
grid on 
hold on 
xx=[-1,-1/2,-1/4,-1/8,-1/16,-1/32,-1/64,-1/128,...     1/128,1/64,1/32,1/16,1/8,1/4,1/2,1]; 
yy=[-1,-7/8,-6/8,-5/8,-4/8,-3/8,-2/8,-1/8,1/8,2/8,3/8,4/8,5/8,6/8,7/8,1]; 
plot(xx,yy,'r') 
stem(xx,yy,'b-.') 
legend('A律壓縮特性','折線近似A律') 
***************************************