Q29240: HOWTO: Converting Colors Between RGB and HLS (HBS)
Article: Q29240
Product(s): Microsoft Windows Software Development Kit
Version(s): WINDOWS:3.1,95; winnt:3.5,3.51,4.0
Operating System(s):
Keyword(s):
Last Modified: 11-MAY-2001
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The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1
- Microsoft Win32 Application Programming Interface (API), used with:
- Microsoft Windows NT Server versions 3.5, 3.51, 4.0
- Microsoft Windows NT Workstation versions 3.5, 3.51, 4.0
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SUMMARY
=======
The code fragment below converts colors between RGB (Red, Green, Blue) and
HLS/HBS (Hue, Lightness, Saturation/Hue, Brightness, Saturation).
MORE INFORMATION
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RGBtoHLS() takes a DWORD RGB value, translates it to HLS, and stores the results
in the global vars H, L, and S. HLStoRGB takes the current values of H, L, and S
and returns the equivalent value in an RGB DWORD. The vars H, L, and S are only
written to by:
1. RGBtoHLS (initialization)
2. The scroll bar handlers
A point of reference for the algorithms is Foley and Van Dam, "Fundamentals of
Interactive Computer Graphics," Pages 618-19. Their algorithm is in floating
point. CHART implements a less general (hardwired ranges) integral algorithm.
There are potential round-off errors throughout this sample. ((0.5 + x)/y)
without floating point is phrased ((x + (y/2))/y), yielding a very small
round-off error. This makes many of the following divisions look strange.
*/
#define HLSMAX RANGE /* H,L, and S vary over 0-HLSMAX */
#define RGBMAX 255 /* R,G, and B vary over 0-RGBMAX */
/* HLSMAX BEST IF DIVISIBLE BY 6 */
/* RGBMAX, HLSMAX must each fit in a byte. */
/* Hue is undefined if Saturation is 0 (grey-scale) */
/* This value determines where the Hue scrollbar is */
/* initially set for achromatic colors */
#define UNDEFINED (HLSMAX*2/3)
void RGBtoHLS(lRGBColor)
DWORD lRGBColor;
{
WORD R,G,B; /* input RGB values */
BYTE cMax,cMin; /* max and min RGB values */
WORD Rdelta,Gdelta,Bdelta; /* intermediate value: % of spread from max
*/
/* get R, G, and B out of DWORD */
R = GetRValue(lRGBColor);
G = GetGValue(lRGBColor);
B = GetBValue(lRGBColor);
/* calculate lightness */
cMax = max( max(R,G), B);
cMin = min( min(R,G), B);
L = ( ((cMax+cMin)*HLSMAX) + RGBMAX )/(2*RGBMAX);
if (cMax == cMin) { /* r=g=b --> achromatic case */
S = 0; /* saturation */
H = UNDEFINED; /* hue */
}
else { /* chromatic case */
/* saturation */
if (L <= (HLSMAX/2))
S = ( ((cMax-cMin)*HLSMAX) + ((cMax+cMin)/2) ) / (cMax+cMin);
else
S = ( ((cMax-cMin)*HLSMAX) + ((2*RGBMAX-cMax-cMin)/2) )
/ (2*RGBMAX-cMax-cMin);
/* hue */
Rdelta = ( ((cMax-R)*(HLSMAX/6)) + ((cMax-cMin)/2) ) / (cMax-cMin);
Gdelta = ( ((cMax-G)*(HLSMAX/6)) + ((cMax-cMin)/2) ) / (cMax-cMin);
Bdelta = ( ((cMax-B)*(HLSMAX/6)) + ((cMax-cMin)/2) ) / (cMax-cMin);
if (R == cMax)
H = Bdelta - Gdelta;
else if (G == cMax)
H = (HLSMAX/3) + Rdelta - Bdelta;
else /* B == cMax */
H = ((2*HLSMAX)/3) + Gdelta - Rdelta;
if (H < 0)
H += HLSMAX;
if (H > HLSMAX)
H -= HLSMAX;
}
}
/* utility routine for HLStoRGB */
WORD HueToRGB(n1,n2,hue)
WORD n1;
WORD n2;
WORD hue;
{
/* range check: note values passed add/subtract thirds of range */
if (hue < 0)
hue += HLSMAX;
if (hue > HLSMAX)
hue -= HLSMAX;
/* return r,g, or b value from this tridrant */
if (hue < (HLSMAX/6))
return ( n1 + (((n2-n1)*hue+(HLSMAX/12))/(HLSMAX/6)) );
if (hue < (HLSMAX/2))
return ( n2 );
if (hue < ((HLSMAX*2)/3))
return ( n1 + (((n2-n1)*(((HLSMAX*2)/3)-hue)+(HLSMAX/12))/(HLSMAX/6))
);
else
return ( n1 );
}
DWORD HLStoRGB(hue,lum,sat)
WORD hue;
WORD lum;
WORD sat;
{
WORD R,G,B; /* RGB component values */
WORD Magic1,Magic2; /* calculated magic numbers (really!) */
if (sat == 0) { /* achromatic case */
R=G=B=(lum*RGBMAX)/HLSMAX;
if (hue != UNDEFINED) {
/* ERROR */
}
}
else { /* chromatic case */
/* set up magic numbers */
if (lum <= (HLSMAX/2))
Magic2 = (lum*(HLSMAX + sat) + (HLSMAX/2))/HLSMAX;
else
Magic2 = lum + sat - ((lum*sat) + (HLSMAX/2))/HLSMAX;
Magic1 = 2*lum-Magic2;
/* get RGB, change units from HLSMAX to RGBMAX */
R = (HueToRGB(Magic1,Magic2,hue+(HLSMAX/3))*RGBMAX +
(HLSMAX/2))/HLSMAX;
G = (HueToRGB(Magic1,Magic2,hue)*RGBMAX + (HLSMAX/2)) / HLSMAX;
B = (HueToRGB(Magic1,Magic2,hue-(HLSMAX/3))*RGBMAX +
(HLSMAX/2))/HLSMAX;
}
return(RGB(R,G,B));
}
Additional query words: 3.00 3.10 3.50 4.00 color RGB HLS HBS win16sdk
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Keywords :
Technology : kbAudDeveloper kbSDKSearch kbWin32sSearch kbWin32API kbWinSDKSearch
Version : WINDOWS:3.1,95; winnt:3.5,3.51,4.0
Issue type : kbhowto
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