#define min3v(v1, v2, v3) ((v1)>(v2)? ((v2)>(v3)?(v3):(v2)):((v1)>(v3)?(v3):(v2)))
#define max3v(v1, v2, v3) ((v1)<(v2)? ((v2)<(v3)?(v3):(v2)):((v1)<(v3)?(v3):(v1)))
typedef struct
{
int red; // [0,255]
int green; // [0,255]
int blue; // [0,255]
}COLOR_RGB;
typedef struct
{
float hue; // [0,360]
float saturation; // [0,100]
float luminance; // [0,100]
}COLOR_HSL;
// Converts RGB to HSL
static void RGBtoHSL(const COLOR_RGB *rgb, COLOR_HSL *hsl)
{
float h=0, s=0, l=0;
// normalizes red-green-blue values
float r = rgb->red/255.0f;
float g = rgb->green/255.0f;
float b = rgb->blue/255.0f;
float maxVal = max3v(r, g, b);
float minVal = min3v(r, g, b);
// hue
if(maxVal == minVal)
{
h = 0; // undefined
}
else if(maxVal==r && g>=b)
{
h = 60.0f*(g-b)/(maxVal-minVal);
}
else if(maxVal==r && g<b)
{
h = 60.0f*(g-b)/(maxVal-minVal) + 360.0f;
}
else if(maxVal==g)
{
h = 60.0f*(b-r)/(maxVal-minVal) + 120.0f;
}
else if(maxVal==b)
{
h = 60.0f*(r-g)/(maxVal-minVal) + 240.0f;
}
// luminance
l = (maxVal+minVal)/2.0f;
// saturation
if(l == 0 || maxVal == minVal)
{
s = 0;
}
else if(0<l && l<=0.5f)
{
s = (maxVal-minVal)/(maxVal+minVal);
}
else if(l>0.5f)
{
s = (maxVal-minVal)/(2 - (maxVal+minVal)); //(maxVal-minVal > 0)?
}
hsl->hue = (h>360)? 360 : ((h<0)?0:h);
hsl->saturation = ((s>1)? 1 : ((s<0)?0:s))*100;
hsl->luminance = ((l>1)? 1 : ((l<0)?0:l))*100;
}
// Converts HSL to RGB
static void HSLtoRGB(const COLOR_HSL *hsl, COLOR_RGB *rgb)
{
float h = hsl->hue; // h must be [0, 360]
float s = hsl->saturation/100.f; // s must be [0, 1]
float l = hsl->luminance/100.f; // l must be [0, 1]
float R, G, B;
if(hsl->saturation == 0)
{
// achromatic color (gray scale)
R = G = B = l*255.0f;
}
else
{
float q = (l<0.5f)?(l * (1.0f+s)):(l+s - (l*s));
float p = (2.0f * l) - q;
float Hk = h/360.0f;
float T[3];
T[0] = Hk + 0.3333333f; // Tr 0.3333333f=1.0/3.0
T[1] = Hk; // Tb
T[2] = Hk - 0.3333333f; // Tg
for(int i=0; i<3; i++)
{
if(T[i] < 0) T[i] += 1.0f;
if(T[i] > 1) T[i] -= 1.0f;
if((T[i]*6) < 1)
{
T[i] = p + ((q-p)*6.0f*T[i]);
}
else if((T[i]*2.0f) < 1) //(1.0/6.0)<=T[i] && T[i]<0.5
{
T[i] = q;
}
else if((T[i]*3.0f) < 2) // 0.5<=T[i] && T[i]<(2.0/3.0)
{
T[i] = p + (q-p) * ((2.0f/3.0f) - T[i]) * 6.0f;
}
else T[i] = p;
}
R = T[0]*255.0f;
G = T[1]*255.0f;
B = T[2]*255.0f;
}
rgb->red = (int)((R>255)? 255 : ((R<0)?0 : R));
rgb->green = (int)((G>255)? 255 : ((G<0)?0 : G));
rgb->blue = (int)((B>255)? 255 : ((B<0)?0 : B));
}
// 在Windows系统下，HSL分量的范围是[0，240].参考“画笔”程序，可以看到RGB（红|绿|蓝）
// 和HSL（色调|饱和度|亮度）的联系。
// 下面的代码，把COLOR_HSL的分量值变为Windows的HSL分量，取值在[0，240]之间，需要：
// 下面为COLOR_HSL到Windows的HSL的转换：
// win_H = 240 * hsl.hue / 360.f;
// win_S = 240 * hsl.saturation / 100.f;
// win_L = 240 * hsl.luminance / 100.f;
上面内容转载自http://c.chinaitlab.com/cc/example/200903/780279.html，原文里有些错误，已修正~
下面是C#实现
public struct ColorRGB
{
public byte R;
public byte G;
public byte B;
public ColorRGB(Color value)
{
this.R = value.R;
this.G = value.G;
this.B = value.B;
}
public static implicit operator Color(ColorRGB rgb)
{
Color c = Color.FromArgb(rgb.R,rgb.G,rgb.B);
return c;
}
public static explicit operator ColorRGB(Color c)
{
return new ColorRGB(c);
}
}
// Given H,S,L in range of 0-1
// Returns a Color (RGB struct) in range of 0-255
public static ColorRGB HSL2RGB(double h, double sl, double l)
{
double v;
double r,g,b;
r = l; // default to gray
g = l;
b = l;
v = (l <= 0.5) ? (l * (1.0 + sl)) : (l + sl - l * sl);
if (v > 0)
{
double m;
double sv;
int sextant;
double fract, vsf, mid1, mid2;
m = l + l - v;
sv = (v - m ) / v;
h *= 6.0;
sextant = (int)h;
fract = h - sextant;
vsf = v * sv * fract;
mid1 = m + vsf;
mid2 = v - vsf;
switch (sextant)
{
case 0:
r = v;
g = mid1;
b = m;
break;
case 1:
r = mid2;
g = v;
b = m;
break;
case 2:
r = m;
g = v;
b = mid1;
break;
case 3:
r = m;
g = mid2;
b = v;
break;
case 4:
r = mid1;
g = m;
b = v;
break;
case 5:
r = v;
g = m;
b = mid2;
break;
}
}
ColorRGB rgb;
rgb.R = Convert.ToByte(r * 255.0f);
rgb.G = Convert.ToByte(g * 255.0f);
rgb.B = Convert.ToByte(b * 255.0f);
return rgb;
}
// Given a Color (RGB Struct) in range of 0-255
// Return H,S,L in range of 0-1
public static void RGB2HSL (ColorRGB rgb, out double h, out double s, out double l)
{
double r = rgb.R/255.0;
double g = rgb.G/255.0;
double b = rgb.B/255.0;
double v;
double m;
double vm;
double r2, g2, b2;
h = 0; // default to black
s = 0;
l = 0;
v = Math.Max(r,g);
v = Math.Max(v,b);
m = Math.Min(r,g);
m = Math.Min(m,b);
l = (m + v) / 2.0;
if (l <= 0.0)
{
return;
}
vm = v - m;
s = vm;
if (s > 0.0)
{
s /= (l <= 0.5) ? (v + m ) : (2.0 - v - m) ;
}
else
{
return;
}
r2 = (v - r) / vm;
g2 = (v - g) / vm;
b2 = (v - b) / vm;
if (r == v)
{
h = (g == m ? 5.0 + b2 : 1.0 - g2);
}
else if (g == v)
{
h = (b == m ? 1.0 + r2 : 3.0 - b2);
}
else
{
h = (r == m ? 3.0 + g2 : 5.0 - r2);
}
h /= 6.0;
}
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