1.RGB转HSV

  max=max(R,G,B) 
  min=min(R,G,B) 
  if R = max, H = (G-B)/(max-min) 
  if G = max, H = 2 + (B-R)/(max-min) 
  if B = max, H = 4 + (R-G)/(max-min) 
  
  H = H * 60 
  if H < 0, H = H + 360 
  
 V=max(R,G,B) 
 S=(max-min)/max 

2. HSV转RGB

 if s = 0 
 R=G=B=V 
 else 
 H /= 60; 
 i = INTEGER(H) 
 
 f = H - i 
 a = V * ( 1 - s ) 
 b = V * ( 1 - s * f ) 
 c = V * ( 1 - s * (1 - f ) ) 
 
 switch(i) 
 case 0: R = V; G = c; B = a; 
 case 1: R = b; G = v; B = a; 
 case 2: R = a; G = v; B = c; 
 case 3: R = a; G = b; B = v; 
 case 4: R = c; G = a; B = v; 
 case 5: R = v; G = a; B = b; 

GLSL CODE

vec3 rgb2hsv(vec3 c) {
    vec4 K = vec4(0.0, -1.0 / 3.0, 2.0 / 3.0, -1.0);
    vec4 p = mix(vec4(c.bg, K.wz), vec4(c.gb, K.xy), step(c.b, c.g));
    vec4 q = mix(vec4(p.xyw, c.r), vec4(c.r, p.yzx), step(p.x, c.r));

    float d = q.x - min(q.w, q.y);
    float e = 1.0e-10;
    return vec3(abs(q.z + (q.w - q.y) / (6.0 * d + e)), d / (q.x + e), q.x);
}
vec3 hsv2rgb(vec3 c) {
    vec4 K = vec4(1.0, 2.0 / 3.0, 1.0 / 3.0, 3.0);
    vec3 p = abs(fract(c.xxx + K.xyz) * 6.0 - K.www);
    return c.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), c.y);
}