Algorithm to Convert Rgb to Hsv and Hsv to Rgb in Range 0-255 For Both

Algorithm to convert RGB to HSV and HSV to RGB in range 0-255 for both

I've used these for a long time - no idea where they came from at this point... Note that the inputs and outputs, except for the angle in degrees, are in the range of 0 to 1.0.

NOTE: this code does no real sanity checking on inputs. Proceed with caution!

typedef struct {
    double r;       // a fraction between 0 and 1
    double g;       // a fraction between 0 and 1
    double b;       // a fraction between 0 and 1
} rgb;

typedef struct {
    double h;       // angle in degrees
    double s;       // a fraction between 0 and 1
    double v;       // a fraction between 0 and 1
} hsv;

static hsv   rgb2hsv(rgb in);
static rgb   hsv2rgb(hsv in);

hsv rgb2hsv(rgb in)
{
    hsv         out;
    double      min, max, delta;

    min = in.r < in.g ? in.r : in.g;
    min = min  < in.b ? min  : in.b;

    max = in.r > in.g ? in.r : in.g;
    max = max  > in.b ? max  : in.b;

    out.v = max;                                // v
    delta = max - min;
    if (delta < 0.00001)
    {
        out.s = 0;
        out.h = 0; // undefined, maybe nan?
        return out;
    }
    if( max > 0.0 ) { // NOTE: if Max is == 0, this divide would cause a crash
        out.s = (delta / max);                  // s
    } else {
        // if max is 0, then r = g = b = 0              
        // s = 0, h is undefined
        out.s = 0.0;
        out.h = NAN;                            // its now undefined
        return out;
    }
    if( in.r >= max )                           // > is bogus, just keeps compilor happy
        out.h = ( in.g - in.b ) / delta;        // between yellow & magenta
    else
    if( in.g >= max )
        out.h = 2.0 + ( in.b - in.r ) / delta;  // between cyan & yellow
    else
        out.h = 4.0 + ( in.r - in.g ) / delta;  // between magenta & cyan

    out.h *= 60.0;                              // degrees

    if( out.h < 0.0 )
        out.h += 360.0;

    return out;
}


rgb hsv2rgb(hsv in)
{
    double      hh, p, q, t, ff;
    long        i;
    rgb         out;

    if(in.s <= 0.0) {       // < is bogus, just shuts up warnings
        out.r = in.v;
        out.g = in.v;
        out.b = in.v;
        return out;
    }
    hh = in.h;
    if(hh >= 360.0) hh = 0.0;
    hh /= 60.0;
    i = (long)hh;
    ff = hh - i;
    p = in.v * (1.0 - in.s);
    q = in.v * (1.0 - (in.s * ff));
    t = in.v * (1.0 - (in.s * (1.0 - ff)));

    switch(i) {
    case 0:
        out.r = in.v;
        out.g = t;
        out.b = p;
        break;
    case 1:
        out.r = q;
        out.g = in.v;
        out.b = p;
        break;
    case 2:
        out.r = p;
        out.g = in.v;
        out.b = t;
        break;

    case 3:
        out.r = p;
        out.g = q;
        out.b = in.v;
        break;
    case 4:
        out.r = t;
        out.g = p;
        out.b = in.v;
        break;
    case 5:
    default:
        out.r = in.v;
        out.g = p;
        out.b = q;
        break;
    }
    return out;     
}

HSV (0 .. 255) to RGB (0 .. 255)

Found it here
http://mjijackson.com/2008/02/rgb-to-hsl-and-rgb-to-hsv-color-model-conversion-algorithms-in-javascript

function hsvToRgb(h, s, v){
    var r, g, b;

    var i = Math.floor(h * 6);
    var f = h * 6 - i;
    var p = v * (1 - s);
    var q = v * (1 - f * s);
    var t = v * (1 - (1 - f) * s);

    switch(i % 6){
        case 0: r = v, g = t, b = p; break;
        case 1: r = q, g = v, b = p; break;
        case 2: r = p, g = v, b = t; break;
        case 3: r = p, g = q, b = v; break;
        case 4: r = t, g = p, b = v; break;
        case 5: r = v, g = p, b = q; break;
    }

    return [r * 255, g * 255, b * 255];
}

Edit:

I once wrote a color picker and used to understand all these. Back then, I looked at photoshop color picker, tried moving around the cross hair, observe the changes in hsv/rgb numbers and figured out how they work. In this case i seems to locate at which point the main color, hue, is pointed it. The value of hue is actually a degree of fully saturated colors in cycle which starts with red and ends with red. There's a triangle with each point representing R,G and B where 0 degree is R. Between R and G, it's Yellow, between R and B, it's Magenta and between B and G, it's cyan. There we have total 6 colors. Those 6 colors are from case 0 through 5.

RGB to HSV in PHP

<?php
function RGB_TO_HSV ($R, $G, $B)  // RGB Values:Number 0-255
{                                 // HSV Results:Number 0-1
   $HSL = array();

   $var_R = ($R / 255);
   $var_G = ($G / 255);
   $var_B = ($B / 255);

   $var_Min = min($var_R, $var_G, $var_B);
   $var_Max = max($var_R, $var_G, $var_B);
   $del_Max = $var_Max - $var_Min;

   $V = $var_Max;

   if ($del_Max == 0)
   {
      $H = 0;
      $S = 0;
   }
   else
   {
      $S = $del_Max / $var_Max;

      $del_R = ( ( ( $var_Max - $var_R ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
      $del_G = ( ( ( $var_Max - $var_G ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;
      $del_B = ( ( ( $var_Max - $var_B ) / 6 ) + ( $del_Max / 2 ) ) / $del_Max;

      if      ($var_R == $var_Max) $H = $del_B - $del_G;
      else if ($var_G == $var_Max) $H = ( 1 / 3 ) + $del_R - $del_B;
      else if ($var_B == $var_Max) $H = ( 2 / 3 ) + $del_G - $del_R;

      if ($H<0) $H++;
      if ($H>1) $H--;
   }

   $HSL['H'] = $H;
   $HSL['S'] = $S;
   $HSL['V'] = $V;

   return $HSL;
}

How to Convert RGB Color to HSV?

Have you considered simply using System.Drawing namespace? For example:

System.Drawing.Color color = System.Drawing.Color.FromArgb(red, green, blue);
float hue = color.GetHue();
float saturation = color.GetSaturation();
float lightness = color.GetBrightness();

Note that it's not exactly what you've asked for (see differences between HSL and HSV and the Color class does not have a conversion back from HSL/HSV but the latter is reasonably easy to add.

HSL to RGB color conversion

Found the easiest way, python to the rescue :D

colorsys.hls_to_rgb(h, l, s)

Convert the color from HLS coordinates to RGB coordinates.

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