PHPBuilder - Determine the tone of web colors



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Determine the tone of web colors

by: Lem Apperson
|
August 9, 2001

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;
}

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