rgbToHsi static method

HsiColor rgbToHsi(RgbColor rgbColor)

Converts a RGB color to a HSI color.

Implementation

static HsiColor rgbToHsi(RgbColor rgbColor) {
  if (rgbColor.isBlack) return HsiColor(0, 0, 0, rgbColor.alpha);
  if (rgbColor.isWhite) return HsiColor(0, 0, 100, rgbColor.alpha);
  if (rgbColor.isMonochromatic) {
    return HsiColor(0, 0, rgbColor.red / 255 * 100, rgbColor.alpha);
  }

  final rgb = rgbColor.toPreciseList();
  final sum = rgb.reduce((a, b) => a + b);
  final red = rgb[0] / sum;
  final green = rgb[1] / sum;
  final blue = rgb[2] / sum;

  var hue = math.acos((0.5 * ((red - green) + (red - blue))) /
      math.sqrt(
          ((red - green) * (red - green)) + ((red - blue) * (green - blue))));

  if (blue > green) hue = (2 * math.pi) - hue;

  if (hue.isNaN) {
    // Achromatic
    hue = 0;
  } else {
    hue /= math.pi * 2;
  }

  final min = <double>[red, green, blue].reduce(math.min);
  final saturation = 1 - 3 * min;
  final intensity = sum / 3 / 255;
  final alpha = rgbColor.alpha / 255;

  return HsiColor.extrapolate(<double>[hue, saturation, intensity, alpha]);
}