RGB HSI HSV HSB HSL
HSI：色相（hue），饱和度（saturation），亮度（Intensity），这种模型完全对应于RGB模型转化而来，转化也有严格的公式推导得到，网上提供了几种转化公式的表示方法：
HSV：色相（hue），饱和度（saturation），明度（value），也称HSB（brightness）。
HSL：色相（hue），饱和度（saturation），亮度（luminance）。
上面这两种模型各个意义也不完全一样，它们的意义对应于它们各自的建模方式。其中HSV/HSB来自于Lab建模方式并考虑了人眼的影响之后得到的。
通用的RGB转HSV/HSB公式如下：详细的原理还未弄清楚
R,G,B的取值范围是[0, Cmax]，未作归一化的Cmax的值为255。Chigh = max(R,G,B)，Clow = min(R,G,B)，Crng = Chigh - Clow
饱和度：
if(Chigh > 0) S = Crng / Chigh else S = 0
明度：
V = Chigh / Cmax
色调：
if(Crng == 0)此时饱和度S == 0，为灰度图，色调因此无定义。
else
先将各分量归一化：R' = (Chigh - R) / Crng G' = (Chigh - G) / Crng B' = (Chigh - B) / Crng
基于原始颜色分量中的最大值，计算出一个初步的色调H'：
if(R = Chigh) H' = B' - G' ; else if(G = Chigh) H' = R' - B' + 2; else if(B = Chigh) H' = G' - R' + 4;
由上式可知H'的取值区间为[-1, 5]，通过将其归一化到区间[0, 1]得到最终的色调值：
if(H' < 0) H = 1/6 * (H' + 6) else H = 1/6 * H'
三个分量值都位于区间[0, 1]。
代码如下：来自于JDK java.awt.Color类
public static float[] RGBtoHSB(int r, int g, int b, float[] hsbvals) {
float hue, saturation, brightness;
if (hsbvals == null) {
hsbvals = new float[3];
}
int cmax = (r > g) ? r : g;
if (b > cmax) cmax = b;
int cmin = (r < g) ? r : g;
if (b < cmin) cmin = b;
brightness = ((float) cmax) / 255.0f;
if (cmax != 0)
saturation = ((float) (cmax - cmin)) / ((float) cmax);
else
saturation = 0;
if (saturation == 0)
hue = 0;
else {
float redc = ((float) (cmax - r)) / ((float) (cmax - cmin));
float greenc = ((float) (cmax - g)) / ((float) (cmax - cmin));
float bluec = ((float) (cmax - b)) / ((float) (cmax - cmin));
if (r == cmax)
hue = bluec - greenc;
else if (g == cmax)
hue = 2.0f + redc - bluec;
else
hue = 4.0f + greenc - redc;
hue = hue / 6.0f;
if (hue < 0)
hue = hue + 1.0f;
}
hsbvals[0] = hue;
hsbvals[1] = saturation;
hsbvals[2] = brightness;
return hsbvals;
}
HSB/HSV转RGB的介绍不给出，直接给出java.awt.Color类中的转换代码
public static int HSBtoRGB(float hue, float saturation, float brightness) {
int r = 0, g = 0, b = 0;
if (saturation == 0) {
r = g = b = (int) (brightness * 255.0f + 0.5f);
} else {
float h = (hue - (float)Math.floor(hue)) * 6.0f;
float f = h - (float)java.lang.Math.floor(h);
float p = brightness * (1.0f - saturation);
float q = brightness * (1.0f - saturation * f);
float t = brightness * (1.0f - (saturation * (1.0f - f)));
switch ((int) h) {
case 0:
r = (int) (brightness * 255.0f + 0.5f);
g = (int) (t * 255.0f + 0.5f);
b = (int) (p * 255.0f + 0.5f);
break;
case 1:
r = (int) (q * 255.0f + 0.5f);
g = (int) (brightness * 255.0f + 0.5f);
b = (int) (p * 255.0f + 0.5f);
break;
case 2:
r = (int) (p * 255.0f + 0.5f);
g = (int) (brightness * 255.0f + 0.5f);
b = (int) (t * 255.0f + 0.5f);
break;
case 3:
r = (int) (p * 255.0f + 0.5f);
g = (int) (q * 255.0f + 0.5f);
b = (int) (brightness * 255.0f + 0.5f);
break;
case 4:
r = (int) (t * 255.0f + 0.5f);
g = (int) (p * 255.0f + 0.5f);
b = (int) (brightness * 255.0f + 0.5f);
break;
case 5:
r = (int) (brightness * 255.0f + 0.5f);
g = (int) (p * 255.0f + 0.5f);
b = (int) (q * 255.0f + 0.5f);
break;
}
}
return 0xff000000 | (r << 16) | (g << 8) | (b << 0);
}
RGB转HSL：
色调：
同HSV
亮度:
L = (Chigh + Clow) / 2
饱和度：
if(L == 0) S = 0; else if( 0<L<=0.5 ) S = 0.5 * Crng / L; else if(0.5 < L < 1) S = 0.5 * Crng / (1 - L); else if(L == 1) S = 0;
static float[] RGBtoHLS(float R, float G, float B){
float cHi = Math.max(R, Math.max(G, B));
float cLo = Math.min(R, Math.min(G, B));
float cRng = cHi - cLo;
//计算亮度L
float L = (cHi + cLo) / 2;
//计算饱和度S
float S = 0;
if(0 < L && L < 1){
float d = (L <= 0.5f) ? L : (1 - L);
S = 0.5f * cRng / d;
}
//计算色调H
float H = 0;
if(cRng > 0){
float rr = (float)((cHi - R) / cRng);
float gg = (float)((cHi - G) / cRng);
float bb = (float)((cHi - B) / cRng);
float hh = 0;
if(R == cHi)hh = bb - gg;
else if(G == cHi)hh = rr - bb + 2;
else if(B == cHi)hh = gg - rr + 4;
if(hh < 0)hh = hh + 6;
H = hh / 6;
}
return new float[]{H, L, S};
}
HSL转RGB代码如下：
static float[] HLStoRGB(float H, float S, float L){
//假设HSL在[0, 1]区间
float R = 0;
float G = 0;
float B = 0;
if(L <= 0)R = G = B = 0;
else if(L >= 1) R = G = B = 1;
else{
float hh = (6 * H) % 6;
int c1 = (int)hh;
float c2 = hh - c1;
float d = (L <= 0.5f) ? (S * L) : (S * (1 - L));
float w = L + d;
float x = L - d;
float y = w - (w - x) * c2;
float z = w + (w - x) * c2;
switch(c1){
case 0: R = w; G = z; B = x; break;
case 1: R = y; G = w; B = x; break;
case 2: R = x; G = w; B = z; break;
case 3: R = x; G = y; B = w; break;
case 4: R = z; G = x; B = w; break;
case 5: R = w; G = x; B = y; break;
}
}
return new float[]{R, G, B};
}
