How do I determine darker or lighter color variant of a given color?

Question

Given a source color of any hue by the system or user, I\'d like a simple algorithm I can use to work out a lighter or darker variants of the selected color. Similar to effe

Answer 1

HSV ( Hue / Saturation / Value ) also called HSL ( Hue / Saturation / Lightness ) is just a different color representation.

Using this representation is it easier to adjust the brightness. So convert from RGB to HSV, brighten the 'V', then convert back to RGB.

Below is some C code to convert

void RGBToHSV(unsigned char cr, unsigned char cg, unsigned char cb,double *ph,double *ps,double *pv)
{
double r,g,b;
double max, min, delta;

/* convert RGB to [0,1] */

r = (double)cr/255.0f;
g = (double)cg/255.0f;
b = (double)cb/255.0f;

max = MAXx(r,(MAXx(g,b)));
min = MINx(r,(MINx(g,b)));

pv[0] = max;

/* Calculate saturation */

if (max != 0.0)
    ps[0] = (max-min)/max;
else
    ps[0] = 0.0; 

if (ps[0] == 0.0)
{
    ph[0] = 0.0f;   //UNDEFINED;
    return;
}
/* chromatic case: Saturation is not 0, so determine hue */
delta = max-min;

if (r==max)
{
    ph[0] = (g-b)/delta;
}
else if (g==max)
{
    ph[0] = 2.0 + (b-r)/delta;
}
else if (b==max)
{
    ph[0] = 4.0 + (r-g)/delta;
}
ph[0] = ph[0] * 60.0;
if (ph[0] < 0.0)
    ph[0] += 360.0;
}

void HSVToRGB(double h,double s,double v,unsigned char *pr,unsigned char *pg,unsigned char *pb)
{
int i;
double f, p, q, t;
double r,g,b;

if( s == 0 )
{
    // achromatic (grey)
    r = g = b = v;
}
else
{
    h /= 60;            // sector 0 to 5
    i = (int)floor( h );
    f = h - i;          // factorial part of h
    p = v * ( 1 - s );
    q = v * ( 1 - s * f );
    t = v * ( 1 - s * ( 1 - f ) );
    switch( i )
    {
    case 0:
        r = v;
        g = t;
        b = p;
    break;
    case 1:
        r = q;
        g = v;
        b = p;
    break;
    case 2:
        r = p;
        g = v;
        b = t;
    break;
    case 3:
        r = p;
        g = q;
        b = v;
    break;
    case 4:
        r = t;
        g = p;
        b = v;
    break;
    default:        // case 5:
        r = v;
        g = p;
        b = q;
    break;
    }
}
r*=255;
g*=255;
b*=255;

pr[0]=(unsigned char)r;
pg[0]=(unsigned char)g;
pb[0]=(unsigned char)b;
}