/// <summary>
/// Convert HSI colorspace to RGB colorspace
/// </summary>
/// <param name="hsi">Input HSI pixel</param>
/// <returns>RGB colorspace pixel</returns>
public static RGB HSI2RGB(this HSI hsi)
{
double r, g, b;
double h = hsi.Hue;
double s = hsi.Saturation;
double i = hsi.Intensity;
h = h * 2 * Math.PI;
if (h >= 0 && h < 2 * Math.PI / 3)
{
b = i * (1 - s);
r = i * (1 + s * Math.Cos(h) / Math.Cos(Math.PI / 3 - h));
g = 3 * i - (r + b);
}
else if (h >= 2 * Math.PI / 3 && h < 4 * Math.PI / 3)
{
r = i * (1 - s);
g = i * (1 + s * Math.Cos(h - 2 * Math.PI / 3) / Math.Cos(Math.PI - h));
b = 3 * i - (r + g);
}
else //if (h >= 4 * Math.PI / 3 && h <= 2 * Math.PI)
{
g = i * (1 - s);
b = i * (1 + s * Math.Cos(h - 4 * Math.PI / 3) / Math.Cos(5 * Math.PI / 3 - h));
r = 3 * i - (g + b);
}
return(new RGB((byte)(r * 255.0 + .5), (byte)(g * 255.0 + .5), (byte)(b * 255.0 + .5)));
}
public static Color ChangeSatuation(Color color, double p)
{
RGB rgb = new RGB(color.R, color.G, color.B);
HSI hsi = ColorspaceHelper.RGB2HSI(rgb);
hsi.Saturation *= p;
rgb = ColorspaceHelper.HSI2RGB(hsi);
return(Color.FromRgb(rgb.Red, rgb.Green, rgb.Blue));
}
/// <summary>
/// Convert RGB colorspace to HSI colorspace
/// </summary>
/// <param name="rgb">Input RGB pixel</param>
/// <returns>HSI colorspace pixel</returns>
public static HSI RGB2HSI(this RGB rgb)
{
HSI hsi = new HSI();
double r = (rgb.Red / 255.0);
double g = (rgb.Green / 255.0);
double b = (rgb.Blue / 255.0);
double theta = Math.Acos(0.5 * ((r - g) + (r - b)) / Math.Sqrt((r - g) * (r - g) + (r - b) * (g - b))) / (2 * Math.PI);
hsi.Hue = (b <= g) ? theta : (1 - theta);
hsi.Saturation = 1 - 3 * Math.Min(Math.Min(r, g), b) / (r + g + b);
hsi.Intensity = (r + g + b) / 3;
return(hsi);
}