Version: N/A
Type: Function
Category: Graphics
License: GNU General Public License
Description: The basic problem that I faced was to determine if I needed to print white or black text over a color background. Since I allowed for the background color to change in my project, I need a way for PHP to determine the color tone. I did some research and the following script is that outcome. Since reds are lighter than either blue are green, I weigh them heavier towards white. This function assigns a tone value in the range of 0 for black to 6 for white. The function then returns the HTML color code for white (FFFFFF) is the background color is dark and black (000000) for all other colors. Now I can sfaely print text on any background, even if I do not know what the actual color is.
function color_shade($colorvalue)
{
// This function accepts a string value ($colorvalue) that is 6 characters long.
//The format of this string follows the web guideline of RRGGBB, where RR is
//a hexidecimal value from 0 to 255(FF) that represents the amount of red in
//a color. BB is the same accept for the amount of Blue and GG is the same for
//Green. There are numerous charts in print and on the Internet that can help
//you to locate a RRGGBB. As an example 808080 is medium gray.
//
// The RRGGBB string is broken into 6 parts. Each part is multiplied by a
//lightness factor. The Red values are lighter than either Blue or Green.
//The values are totaled in a range from 0 to 6 where 0 is the darkest
//and 6 is the lightest.
//
// Finally the function returns a value of either 000000 or FFFFFF. This
//can be used to print text over a color background. I use this to print
//white (FFFFFF) text over dark backgrounds and black (000000) text over
//medim and light backgrounds.
$colorparts = preg_split('//', $colorvalue, -1, PREG_SPLIT_NO_EMPTY);
$tone = array(0.136,0.008,0.038,0.002,0.201,0.013);
$TotalColorValue = 0;
for ($l=0;$l<=5;$l++)
{
$TotalColorValue = (hexdec($colorparts[$l]) * $tone[$l]) + $TotalColorValue;
}
$TotalColorValue = floor($TotalColorValue);
$result = "";
// Values 0 and 1 are dark
if ($TotalColorValue < 2)
{ $result = "FFFFFF"; // Set Text to White
return $result;
}
// Values 2 and 3 are medium
if ( ($TotalColorValue > 1) and ($TotalColorValue < 4) )
{ $result = "000000"; // Set text to Black
return $result;
}
// Values 4 and 5 are light
if ($TotalColorValue > 3 )
{ $result = "000000"; // Set Text to Black
return $result;
}
return $result;
}
