GameProgrammerArt

Pseudo-algorithm:

We are finding the average value for the three color components…

1. Extract the Red, Green and Blue of a color.
2. Add the three values together, divide them by three.
3. Put the Red, Green and Blue values together to form the gray value.

int pixel_value = RGB(13, 152, 186);
//get the red value of the pixel
int red = RED_OF(pixel_value) ;
//get the green value of the pixel
int green = GREEN_OF(pixel_value) ;
//get the blue value of the pixel
int blue BLUE_OF(pixel_value) ;
//average each color together to get the gray value
int gray = (red + green + blue)/3;
//bitwise 'or' them to make the complete RGB
int gray_pixel_value = RGB_OF(gray, gray, gray);

sidenote:
Love these colors from Crayola, they bring back so many memories!

Math

C/C++

pixeltype RGBtoHSV(pixeltype palette_color){
	//0.0f <= r <= 1.0f
	//0.0f <= g <= 1.0f
	//0.0f <= b <= 1.0f
    double r = (double)(RED_OF(palette_color));
    double g = (double)(GREEN_OF(palette_color));
    double b = (double)(BLUE_OF(palette_color));
    double max, min, h, s, v;

	if(r > g){
		max = r;
	}else{
		max = g;
	}
	if(b > max){
		max = b;
	}

	if(r < g){
		min = r;
	}else{
		min = g;
	}
	if(b < min){
		min = b;
	}

    if(max == min){
        h = 0.0f;
    }else if(max == r){
        h = ((60.0f * ((g - b) / (max - min)) + 360) % 360.0f);
    }else if(max == g){
        h = ((60.0f * ((b - r) / (max - min)) + 120));
    }else if(max == b){
        h = ((60.0f * ((r - g) / (max - min)) + 240));
    }

    if(max == 0){
        s = 0.0f;
    }else{
        s = 1.0f - (min / max);
    }
    v = max;

	//0.0f <= h <= 360.0f
	//0.0f <= s <= 1.0f
	//0.0f <= v <= 1.0f
    return HSV_OF(h, s, v);
}

Math

C/C++

pixeltype RGBtoHSV(pixeltype palette_color){
	//0.0f <= r <= 1.0f
	//0.0f <= g <= 1.0f
	//0.0f <= b <= 1.0f
    double r = (double)(RED_OF(palette_color));
    double g = (double)(GREEN_OF(palette_color));
    double b = (double)(BLUE_OF(palette_color));
    double max, min, h, s, l;

	if(r > g){
		max = r;
	}else{
		max = g;
	}
	if(b > max){
		max = b;
	}

	if(r < g){
		min = r;
	}else{
		min = g;
	}
	if(b < min){
		min = b;
	}

    if(max == min){
        h = 0.0f;
    }else if(max == r){
        h = ((60.0f * ((g - b) / (max - min)) + 360) % 360.0f);
    }else if(max == g){
        h = ((60.0f * ((b - r) / (max - min)) + 120));
    }else if(max == b){
        h = ((60.0f * ((r - g) / (max - min)) + 240));
    }

	l = (max + min) / 2.0f;

	if(max == min){
		s = 0;
	}else if(l <= 0.5f){
		s = ((max - min) / (2 * l));
	}else if(l > 0.5f){
		s = ((max - min) / (2 - (2 * l)));
	}

	//0.0f <= h <= 360.0f
	//0.0f <= s <= 1.0f
	//0.0f <= l <= 1.0f
    return HSL_OF(h, s, l);
}
}

Math

C/C++

pixeltype HSLtoRGB(pixeltype palette_color){
	//0.0f <= h <  360.0f
	//0.0f <= s <= 1.0f
	//0.0f <= l <= 1.0f
	double h = (double)(HUE_OF(palette_color));
    double s = (double)(SATURATION_OF(palette_color));
    double l = (double)(LIGHTNESS_OF(palette_color));
	double q, p, h_k;
	double rgb[3];

	if(l < 0.5f){
		q = l * (1 + s);
	}else{
		q = l + s - (l * s);
	}
	p = 2 * l - q;
	h_k = h / 360.0f;
	rgb[0] = h_k + (1 / 3);
	rgb[1] = h_k;
	rgb[2] = h_k - (1 / 3);
	for(size_t i = 0; i < 3; i++){
		if(rgb[i] < (1 / 6)){
			rgb[i] = p + ((q - p) * 6.0f * rgb[i]);
		}else if(rgb[i] >= (1 / 6) && rgb[i] < (1 / 2)){
			rgb[i] = q;
		}else if(rgb[i] >= (1 / 2) && rgb[i] < (2 / 3)){
			rgb[i] = p + ((q - p) * 6.0f * ((2 / 3) - rgb[i]));
		}else{
			rgb[i] = p;
		}
	}
	//0.0f <= rgb[0] <= 1.0f
	//0.0f <= rgb[1] <= 1.0f
	//0.0f <= rgb[2] <= 1.0f
	return RGB_OF(rgb[0], rgb[1], rgb[2]);
}