Cubehelix LUT generator

cubehelix.c

void
cubehelix(
	size_t const n_steps,
	uint8_t * const out_lut, /* 3 * n_steps elements, r8b8g8 */
	double const start, /* start color */
	double const rotations,
	double const hue,
	double const gamma )
{ 
	size_t i;
	for(i = 0; i < n_steps; ++i) {
		double const fract = (double)i / (double)n_steps;
        	double const angle = M_PI*2 * (start/M_PI + 1.0 + rotations * fract);

		double const amp = hue*fract*(1.0 - fract)/2.0;
		double const red = clampf(0.0, 1.0,
			(fract + amp*(-0.14861*cos(angle) + 1.78277*sin(angle))) );

		double const green = clampf(0.0, 1.0,
			(fract + amp*(-0.29227*cos(angle) - 0.90649*sin(angle))) );

		double const blue = clampf(0.0, 1.0,
			(fract + amp*(+1.97294*cos(angle))) );

		double const k = pow( hypot(red, hypot(green, blue)) * 0.57735027, gamma );

		out_lut[3 * i + 0] = roundf(255.f * k * red);
		out_lut[3 * i + 1] = roundf(255.f * k * green);
		out_lut[3 * i + 2] = roundf(255.f * k * blue);
	}
}