how can we minus 15 pixel from bottom height in fitting to create thumbnails for original image in this code ? i mean how can tell php that capture from original image the ( all width ) and ( all height minus -15 pixel from bottom )

Code:
#create thumb
$thumb = gd_fit($image,$settings['thumbxy']);




	function gd_fit(&$image, $target) { 
	
		//takes the larger size of the width and height and applies the  
		//formula accordingly...this is so this script will work  
		//dynamically with any size image 
		
		$width = gd_width($image);
		$height = gd_height($image);
		
		if ($width > $height) { 
			$percentage = ($target / $width); 
		} else { 
			$percentage = ($target / $height); 
		} 
		
		//gets the new value and applies the percentage, then rounds the value 
		$width = round($width * $percentage); 
		$height = round($height * $percentage); 
		
		//returns the new sizes in html image tag format...this is so you 
		//can plug this function inside an image tag and just get the 
		
		return gd_resize($image,$width,$height);
		
	}