代码来自http://www.cocoabuilder.com/archive/cocoa/198570-here-is-code-to-convert-rgb-hsb.html

C语言，可在Object-C中调用

#define UNDEFINED 0typedef struct {float r, g, b;} RGBType;
typedef struct {float h, s, v;} HSVType;// Theoretically, hue 0 (pure red) is identical to hue 6 in these transforms. Pure
// red always maps to 6 in this implementation. Therefore UNDEFINED can be
// defined as 0 in situations where only unsigned numbers are desired.
RGBType RGBTypeMake(float r, float g, float b);
HSVType HSVTypeMake(float h, float s, float v);HSVType RGB_to_HSV( RGBType RGB );
RGBType HSV_to_RGB( HSVType HSV );

#include <math.h>
#include "HSV.h"inline RGBType RGBTypeMake(float r, float g, float b)
{RGBType rgb = {r, g, b};return rgb;
}inline HSVType HSVTypeMake(float h, float s, float v)
{HSVType hsv = {h, s, v};return hsv;
}HSVType RGB_to_HSV( RGBType RGB )
{// RGB are each on [0, 1]. S and V are returned on [0, 1] and H is// returned on [0, 1]. Exception: H is returned UNDEFINED if S==0.float R = RGB.r, G = RGB.g, B = RGB.b, v, x, f;int i;x = fminf(R, G);x = fminf(x, B);v = fmaxf(R, G);v = fmaxf(v, B);if(v == x) return HSVTypeMake(UNDEFINED, 0, v);f = (R == x) ? G - B : ((G == x) ? B - R : R - G);i = (R == x) ? 3 : ((G == x) ? 5 : 1);return HSVTypeMake(((i - f /(v - x))/6), (v - x)/v, v);
}RGBType HSV_to_RGB( HSVType HSV )
{// H is given on [0, 1] or UNDEFINED. S and V are given on [0, 1].// RGB are each returned on [0, 1].float h = HSV.h * 6, s = HSV.s, v = HSV.v, m, n, f;int i;if (h == 0) h=.01;if(h == UNDEFINED) return RGBTypeMake(v, v, v);i = floorf(h);f = h - i;if(!(i & 1)) f = 1 - f; // if i is evenm = v * (1 - s);n = v * (1 - s * f);switch (i){case 6:case 0: return RGBTypeMake(v, n, m);case 1: return RGBTypeMake(n, v, m);case 2: return RGBTypeMake(m, v, n);case 3: return RGBTypeMake(m, n, v);case 4: return RGBTypeMake(n, m, v);case 5: return RGBTypeMake(v, m, n);}return RGBTypeMake(0, 0, 0);
}