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

I have used the ControlPaint.Dark() and .Light() in System.Windows.Forms.

Answer 2

Simply multiply the RGB values by the amount you want to modify the level by. If one of the colors is already at the max value, then you can't make it any brighter (using HSV math anyway.)

This gives the exact same result with a lot less math as switching to HSV and then modifying V. This gives the same result as switching to HSL and then modifying L, as long as you don't want to start losing saturation.

Answer 3

The idea of converting to HSV or some other color space seems good, and may be necessary for precise color work, but for ordinary purposes the error of working in RGB may not be enough to matter. Also, it can be a pain to deal with boundary cases: RGB is a cube-shaped space, while HSV is not. If working with byte values, you can have many-to-one and one-to-many mappings between the spaces. This may or may not be a problem depending on the application. YMMV

Answer 4

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;
}

Answer 5

Assuming you get the color as RGB, first convert it to HSV (hue, saturation, value) color space. Then increase/decrease the value to produce lighter/darker shade of the color. Then convert back to RGB.

Answer 6

If you are using RGB colors I would transform this color paramaters to HSL (hue, saturation, lightness), modify the lightness parameter and then transform back to RGB. Google around and you'll find a lot of code samples on how to do these color representation transformations (RGB to HSL and viceversa).

This is what I quickly found: http://bytes.com/forum/thread250450.html