Question

用MATLAB编写RGB到HSL和HSL到RGB颜色空间的转换程序：rgb2hsl.m和hsl2rgb.m

用MATLAB编写RGB到HSL和HSL到RGB颜色空间的转换程序：rgb2hsl.m和hsl2rgb.m

Answer 1

function hsl=rgb2hsl(rgb)

%Converts Red-Green-Blue Color value to Hue-Saturation-Luminance Color value
%
%Usage
% HSL = rgb2hsl(RGB)
%
% converts RGB, a M X 3 color matrix with values between 0 and 1
% into HSL, a M X 3 color matrix with values between 0 and 1
%
%See also hsl2rgb, rgb2hsv, hsv2rgb

%Suresh E Joel, April 26,2003

if nargin<1,
error('Too few arguements for rgb2hsl');
return;
elseif nargin>1,
error('Too many arguements for rgb2hsl');
return;
end;

if max(max(rgb))>1 | min(min(rgb))<0,
error('RGB values have to be between 0 and 1');
return;
end;

for i=1:size(rgb,1),
mx=max(rgb(i,:));%max of the 3 colors
mn=min(rgb(i,:));%min of the 3 colors
imx=find(rgb(i,:)==mx);%which color has the max
hsl(i,3)=(mx+mn)/2;%luminance is half of max value + min value
if(mx-mn)==0,%if all three colors have same value,
hsl(i,2)=0;%then s=0 and
hsl(i,1)=0;%h is undefined but for practical reasons 0
return;
end;
if hsl(i,3)<0.5,
hsl(i,2)=(mx-mn)/(mx+mn);
else
hsl(i,2)=(mx-mn)/(2-(mx+mn));
end;
switch(imx(1))%if two colors have same value and be the maximum, use the first color
case 1 %Red is the max color
hsl(i,1)=((rgb(i,2)-rgb(i,3))/(mx-mn))/6;
case 2 %Green is the max color
hsl(i,1)=(2+(rgb(i,3)-rgb(i,1))/(mx-mn))/6;
case 3 %Blue is the max color
hsl(i,1)=(4+(rgb(i,1)-rgb(i,2))/(mx-mn))/6;
end;
if hsl(i,1)<0,hsl(i,1)=hsl(i,1)+1;end;%if hue is negative, add 1 to get it within 0 and 1
end;

hsl=round(hsl*100000)/100000; %Sometimes the result is 1+eps instead of 1 or 0-eps instead of 0 ... so to get rid of this I am rounding to 5 decimal places)