非常见颜色模式转RGB模式
RGB模式是计算机图像学最常用的颜色模式,除此之外,还有其他非常用的颜色模式,以下列举常用颜色模式转RGB的算法
1. CMYK是印刷业用的颜色模式,它是一种减色模式,与RGB加色模式完全不同,有时我们需要把CMYK转成RGB模式
转换算法:
r = (1-k)-(1-k)*c;
g = (1-k)-(1-k)*m;
b = (1-k)-(1-k)*y;
2. HSB也是一种常见的颜色模式(又称HSV),这个模型中颜色的参数分别是:色调(H),饱和度(S),亮度(B)。色调决定了颜色的名称,如红色色调,S表示色彩的纯度,B表示色彩的明亮度。(以下算法取自Cocos2d-x引擎算法)
RGBA ColorUtil::RGBfromHSV(HSV value) { double hh, p, q, t, ff; long i; RGBA out; out.a = 1; if (value.s <= 0.0) // < is bogus, just shuts up warnings { if (isnan(value.h)) // value.h == NAN { out.r = value.v; out.g = value.v; out.b = value.v; return out; } // error - should never happen out.r = 0.0; out.g = 0.0; out.b = 0.0; return out; } hh = value.h; if(hh >= 360.0) hh = 0.0; hh /= 60.0; i = (long)hh; ff = hh - i; p = value.v * (1.0 - value.s); q = value.v * (1.0 - (value.s * ff)); t = value.v * (1.0 - (value.s * (1.0 - ff))); switch(i) { case 0: out.r = value.v; out.g = t; out.b = p; break; case 1: out.r = q; out.g = value.v; out.b = p; break; case 2: out.r = p; out.g = value.v; out.b = t; break; case 3: out.r = p; out.g = q; out.b = value.v; break; case 4: out.r = t; out.g = p; out.b = value.v; break; case 5: default: out.r = value.v; out.g = p; out.b = q; break; } return out; }
3。LAB颜色模式是模拟人眼对颜色的感觉,理论上,它比上面两种的颜色范围更广更细致,转换算法如下
double L, a, b; double X, Y, Z; double R, G, B; // Lab -> normalized XYZ (X,Y,Z are all in 0...1) Y = L * (1.0/116.0) + 16.0/116.0; X = a * (1.0/500.0) + Y; Z = b * (-1.0/200.0) + Y; X = X > 6.0/29.0 ? X * X * X : X * (108.0/841.0) - 432.0/24389.0; Y = L > 8.0 ? Y * Y * Y : L * (27.0/24389.0); Z = Z > 6.0/29.0 ? Z * Z * Z : Z * (108.0/841.0) - 432.0/24389.0; // normalized XYZ -> linear sRGB (in 0...1) R = X * (1219569.0/395920.0) + Y * (-608687.0/395920.0) + Z * (-107481.0/197960.0); G = X * (-80960619.0/87888100.0) + Y * (82435961.0/43944050.0) + Z * (3976797.0/87888100.0); B = X * (93813.0/1774030.0) + Y * (-180961.0/887015.0) + Z * (107481.0/93370.0); // linear sRGB -> gamma-compressed sRGB (in 0...1) R = R > 0.0031308 ? pow(R, 1.0 / 2.4) * 1.055 - 0.055 : R * 12.92; G = G > 0.0031308 ? pow(G, 1.0 / 2.4) * 1.055 - 0.055 : G * 12.92; B = B > 0.0031308 ? pow(B, 1.0 / 2.4) * 1.055 - 0.055 : B * 12.92;