How to retrieve HSB from CGColor? - iphone

Question

I have a CGColor in my app and I'd like to get the hue, saturation and brightness values from it. How would i be able to access these?

Answer 1

See Duncan Champney's post to cocoa-dev entitled "Here is code to Convert RGB <-> HSB". There, he gives this code:
//------------------
//---header file
#define RETURN_HSV(h, s, v) {HSV.H = h; HSV.S = s; HSV.V = v; return
HSV;}
#define RETURN_RGB(r, g, b) {RGB.R = r; RGB.G = g; RGB.B = b; return
RGB;}
#define UNDEFINED 0
// 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.
typedef struct {float R, G, B;} RGBType;
typedef struct {float H, S, V;} HSVType;
//------------------
//--The code
#include <math.h>
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;
HSVType HSV;
//x = fminx(R, G, B);
x = fminf(R, G);
x = fminf(x, B);
//v = fmaxf(R, G, B);
v = fmaxf(R, G);
v = fmaxf(v, B);
if(v == x) RETURN_HSV(UNDEFINED, 0, v);
f = (R == x) ? G - B : ((G == x) ? B - R : R - G);
i = (R == x) ? 3 : ((G == x) ? 5 : 1);
RETURN_HSV(((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;
RGBType RGB;
if (h == 0) h=.01;
if(h == UNDEFINED) RETURN_RGB(v, v, v);
i = floorf(h);
f = h - i;
if(!(i & 1)) f = 1 - f; // if i is even
m = v * (1 - s);
n = v * (1 - s * f);
switch (i)
{
case 6:
case 0: RETURN_RGB(v, n, m);
case 1: RETURN_RGB(n, v, m);
case 2: RETURN_RGB(m, v, n);
case 3: RETURN_RGB(m, n, v);
case 4: RETURN_RGB(n, m, v);
case 5: RETURN_RGB(v, m, n);
}
RETURN_RGB(0, 0, 0);
}
//------------------