calculate fuzzyness

[hampleman]

Dear image enchanting people,

For my online collage machine I need to make transparent a range of colors between colour X and color Y.

Code: Select all

$image->paintTransparentImage  ( $color_x  , 0  , $fuzzyness );

Before that I need to calculate the fuzzyness between these colors. The common function to calculate the color distance does not work. It gives too high values.

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$col_x = $color_x->getColor();
$col_y = $color_y->getColor();
$fuzzyness = sqrt( pow ($col_x['r'] - $col_y['r'] , 2) + pow( $col_x['g'] - $col_y['g'] , 2) + pow( $col_x['b'] - $col_y['b'] , 2) ) * 256;

Strangely enough the Q16 compiled Imagick gives 8 bits RGB values in the ImagickPixel class, while the fuzzyness needs a 16 bit value, but well, that isn't the question here.
I then tried a rather boorish function that also gave to high values (according to some visual tests) and took too long to calculate the fuzzyness between a whole histogram of colors.

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function fuzz($a,$b){
	//$a:ImagickPixel
	//$b:ImagickPixel	
	//returns:float
	if (is_object($a) && is_object($b)){
		$i =0;
		$hit = false;
		while (!$hit){
			$hit = $a->isSimilar ($b, $i);
			$i ++;
		}		
		return $i;
	}
	else{
		return 0;
	}
}

Please don't laugh!
Does anyone know how Image Magick determines the fuzzyness between two colors?

Thanks in advance,
Fabian

[fmw42]

It has changed just recently to handle transparency differently. see viewtopic.php?f=1&t=17584&hilit=fuzz

[hampleman]

Thanks a lot! That link is just what I needed.
I was almost there with my colorDist function, but I forgot to divide the whole mim under the sqaure root by 3...
Now I can use this function and forget that boorish and slow function fuzz (that does give correct results by the way)

Code: Select all

/**
* calculate color distance betweeen two colors   
* @param $a:ImagickPixel
* @param $b:ImagickPixel	
* @return float */
function colDist($a, $b){
	//@param $a:ImagickPixel
	//@param $b:ImagickPixel	
	//returns a normalized float [0..1]
	if (is_object($a) && is_object($b)){
		//get normalized colors
		$col_a = $a->getColor(1);
		$col_b = $b->getColor(1);				
		return sqrt( ( pow($col_a['r']-$col_b['r'],2) + pow($col_a['g']-$col_b['g'],2) + pow($col_a['b']-$col_b['b'],2))/3); 
	}		
	else{
		return 0;
	}
}