view nonExposed/utils/rgb2hsl.m @ 32:8ce78cacb5cb

replace warning to error display channel

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)