/* TEMPRGB -- Calculate the relative R, G, and B components for a
* black body emitting light at a given temperature.
* The Planck radiation equation is solved directly for
* the R, G, and B wavelengths defined for the CIE 1931
* Standard Colorimetric Observer. The colour
* temperature is specified in degrees Kelvin. */
RGB TempRGB(double temp)
{
// Lambda is the wavelength in microns: 5500 angstroms is 0.55 microns.
double r = Planck(temp, 0.7000);
double g = Planck(temp, 0.5461);
double b = Planck(temp, 0.4358);
RGB rgb = new RGB(r, g, b);
rgb.Divide(rgb.Max);
return(rgb);
}
public Pixel Generate()
{
const double starQuality = 0.5; // Brightness distribution exponent
const double starIntensity = 8; // Brightness scale factor
const double starTintExp = 0.5; // Tint distribution exponent
if ((_random.Next() % 1000) < _starFraction)
{
double v = starIntensity * Math.Pow(1 / (1 - Cast(0, 0.9999)),
starQuality);
if (v > 255)
{
v = 255;
}
/* We make a special case for star colour of zero in order to
* prevent floating point roundoff which would otherwise
* result in more than 256 star colours. We can guarantee
* that if you specify no star colour, you never get more than
* 256 shades in the image. */
if (_starColour == 0)
{
return(new Pixel((byte)v, (byte)v, (byte)v));
}
else
{
double temp = 5500 + _starColour *
Math.Pow(1 / (1 - Cast(0, 0.9999)), starTintExp) *
(((_random.Next() & 7) != 0) ? -1 : 1);
/* Constrain temperature to a reasonable value: >= 2600K
* (S Cephei/R Andromedae), <= 28,000 (Spica). */
temp = Math.Max(2600, Math.Min(28000, temp));
RGB rgb = TempRGB(temp);
rgb.Multiply(v);
rgb.Add(new RGB(0.499, 0.499, 0.499));
rgb.Divide(255);
return(new Pixel(rgb.Bytes));
}
}
else
{
return(new Pixel(3));
}
}
/* TEMPRGB -- Calculate the relative R, G, and B components for a
black body emitting light at a given temperature.
The Planck radiation equation is solved directly for
the R, G, and B wavelengths defined for the CIE 1931
Standard Colorimetric Observer. The colour
temperature is specified in degrees Kelvin. */
RGB TempRGB(double temp)
{
// Lambda is the wavelength in microns: 5500 angstroms is 0.55 microns.
double r = Planck(temp, 0.7000);
double g = Planck(temp, 0.5461);
double b = Planck(temp, 0.4358);
RGB rgb = new RGB(r, g, b);
rgb.Divide(rgb.Max);
return rgb;
}
