How should I prevent colors that cannot be seen?

Question

I have this code:

function rand_colorCode(){
  $r = dechex(mt_rand(0,255));
  $g = dechex(mt_rand(0,255));
  $b = dechex(mt_rand(0,255));
  $rgb = $r.$g.$b;
  if($r == $g && $g == $b){
    $rgb = substr($rgb,0,3);
  }
  return '#'.$rgb;
}

$code = rand_colorCode();

This generates a random color which later gets inserted into the mysql db. But sometimes it generates too light color. (this is a problem because these colors are later displayed and my background color is white)

My simple question is: How can I prevent colors being too light or too dark? How should I customize my code?

I suggest you re-evaluate your approach. Using a limit - 50-200 instead of 0,255 - would eliminate red(255,0,0), green(0,255,0) and blue(0,0,255) from possible generated colors. — Luchian Grigore, Oct 28 '11 at 13:57

score 2 · Answer 1 · answered Oct 28 '11 at 11:34

2

Use a shorter color range:

mt_rand(80,200)

The lower boundary prevents near-black colors, while the higher boundary prevents near-white colors. You can adjust this range to suit your needs.

answered Oct 28 '11 at 11:34

Evan Mulawski

54,662
15
117
144

score 2 · Answer 2 · edited May 23 '17 at 11:47

2

You can calculate the brightness of the current set of colors and validate it according to some predefined limits:

while ( true )
{
  $r = dechex(mt_rand(0,255));
  $g = dechex(mt_rand(0,255));
  $b = dechex(mt_rand(0,255));
  $brightness = ( 0.2126 * $r ) + ( 0.7152 * $g ) + ( 0.0722 * $b )
  if ( $brightness > $lower_limit || $brightness < $upper_limit )
     break;
}

The formula is taken from here Formula to determine brightness of RGB color

edited May 23 '17 at 11:47

Community

1
1

answered Oct 28 '11 at 11:42

Luchian Grigore

253,575
64
457
625

+1 Though I think that the 2nd or 3rd formulas were more applicable – NikiC Oct 28 '11 at 11:49

score 0 · Accepted Answer · answered Oct 28 '11 at 11:37

Well the RGB code of (for instance) white is 255, 255, 255. You can just define a rule that if all three values (R, G & B) are above a certain treshold, the color will be too light and will thus not display correctly. Try to define a treshold yourself by having a look at a color palet. Maybe 200, 200, 200 would be the maximum you'd want and 50, 50, 50 the minimum.

You can then just randomize a color from 50 up to 200 (if you define that as your treshold). So instead of

 $r = dechex(mt_rand(0,255));

You do

 $r = dechex(mt_rand(50,200));

This could be an easy way to fix it.

This would exclude pure colors like 0,0,255; 0,255,0; 255,0,0 which are blue, green and red and has nothing to do with a black/white background. — Luchian Grigore, Oct 28 '11 at 13:55

How should I prevent colors that cannot be seen?

3 Answers3