Colour Model Conversions

Does anybody out there know a decent RGB to HSL color model conversion algorithm.
LVL 4
StevenBAsked:
Who is Participating?

[Product update] Infrastructure Analysis Tool is now available with Business Accounts.Learn More

x
I wear a lot of hats...

"The solutions and answers provided on Experts Exchange have been extremely helpful to me over the last few years. I wear a lot of hats - Developer, Database Administrator, Help Desk, etc., so I know a lot of things but not a lot about one thing. Experts Exchange gives me answers from people who do know a lot about one thing, in a easy to use platform." -Todd S.

erajojCommented:
This is NOT Delphi code as you can see.
There should not be a problem for you to port
this though.
From "Fundamentals of Interactive Computer Graphics" by Foley and van Dam:


void RGBtoHSL( COLORREF rgb, double *H, double *S, double *L )
{
   double delta;
   double r = (double)GetRValue(rgb)/255;
   double g = (double)GetGValue(rgb)/255;
   double b = (double)GetBValue(rgb)/255;
   double cmax = max(r,max(g,b));
   double cmin = min(r,min(g,b));
   *L=(cmax+cmin)/2.0;
   if(cmax==cmin) {
      *S = 0;
      *H = 0; // it's really undefined
   } else {
      if(*L < 0.5)
         *S = (cmax-cmin)/(cmax+cmin);
      else
         *S = (cmax-cmin)/(2.0-cmax-cmin);
      delta = cmax - cmin;
      if(r==cmax)
          *H = (g-b)/delta;
      else if(g==cmax)
          *H = 2.0 +(b-r)/delta;
      else
          *G=4.0+(r-g)/delta;
      *H /= 6.0;
      if(*H < 0.0)
          *H += 1;
   }
}

To convert HSL to RGB use code like this:

static double HuetoRGB(double m1, double m2, double h )
{
   if( h < 0 ) h += 1.0;
   if( h > 1 ) h -= 1.0;
   if( 6.0*h < 1 )
      return (m1+(m2-m1)*h*6.0);
   if( 2.0*h < 1 )
      return m2;
   if( 3.0*h < 2.0 )
      return (m1+(m2-m1)*((2.0/3.0)-h)*6.0);
   return m1;
}

COLORREF HLStoRGB( double H, double L, double S )
{
  double r,g,b;
  double m1, m2;

  if(S==0) {
     r=g=b=L;
  } else {
     if(L <=0.5)
        m2 = L*(1.0+S);
     else
        m2 = L+S-L*S;
     m1 = 2.0*L-m2;
     r = HuetoRGB(m1,m2,H+1.0/3.0);
     g = HuetoRGB(m1,m2,H);
     b = HuetoRGB(m1,m2,H-1.0/3.0);
  }
  return RGB((BYTE)(r*255),(BYTE)(g*255),(BYTE)(b*255));
}


0

Experts Exchange Solution brought to you by

Your issues matter to us.

Facing a tech roadblock? Get the help and guidance you need from experienced professionals who care. Ask your question anytime, anywhere, with no hassle.

Start your 7-day free trial
StevenBAuthor Commented:
Cheers, Steven.
0
It's more than this solution.Get answers and train to solve all your tech problems - anytime, anywhere.Try it for free Edge Out The Competitionfor your dream job with proven skills and certifications.Get started today Stand Outas the employee with proven skills.Start learning today for free Move Your Career Forwardwith certification training in the latest technologies.Start your trial today
Delphi

From novice to tech pro — start learning today.