api.watermark.php

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<?php
/**
 * Watermarking API
 * @author $Author: Brian Vaughn $ http://boynamedbri.com/  -  http://portfolio.boynamedbri.com/ -  @ devshed http://www.devshed.com/c/a/PHP/Dynamic-Watermarking-with-PHP/
 * @author $Author: Paul Moers <[e-mail]> $ - small changes to place the watermark on a given coordinate and to only handle watermark area
 * @package ImageManager
 */

class watermark{

	# given two images, return a blended watermarked image
	function create_watermark( $main_img_obj, $watermark_img_obj, $alpha_level = 100, $watermarkX = -1, $watermarkY = -1 ) {
		$alpha_level	/= 100;	# convert 0-100 (%) alpha to decimal
	
		# calculate our images dimensions
		$main_img_obj_w	= imagesx( $main_img_obj );
		$main_img_obj_h	= imagesy( $main_img_obj );
		$watermark_img_obj_w	= imagesx( $watermark_img_obj );
		$watermark_img_obj_h	= imagesy( $watermark_img_obj );
		
		# determine watermark area for given coordinates
		if ($watermarkX > - 1 && $watermarkY > -1)
		{
			$main_img_obj_min_x	= $watermarkX;
			$main_img_obj_max_x	= $watermarkX + $watermark_img_obj_w;
			$main_img_obj_min_y	= $watermarkY;
			$main_img_obj_max_y	= $watermarkY + $watermark_img_obj_h;
		}
		# determine watermark area when centered
		else
		{
			$main_img_obj_min_x	= floor( ( $main_img_obj_w / 2 ) - ( $watermark_img_obj_w / 2 ) );
			$main_img_obj_max_x	= ceil( ( $main_img_obj_w / 2 ) + ( $watermark_img_obj_w / 2 ) );
			$main_img_obj_min_y	= floor( ( $main_img_obj_h / 2 ) - ( $watermark_img_obj_h / 2 ) );
			$main_img_obj_max_y	= ceil( ( $main_img_obj_h / 2 ) + ( $watermark_img_obj_h / 2 ) );
		}

		# create image copy to hold merged changes
		$return_img	= $main_img_obj;

		# walk through the watermark area
		for( $y = $main_img_obj_min_y; $y < $main_img_obj_max_y; $y++ ) {
			for( $x = $main_img_obj_min_x; $x < $main_img_obj_max_x; $x++ ) {
				$return_color	= NULL;
				
				# determine the correct pixel location within our watermark
				$watermark_x	= $x - $main_img_obj_min_x;
				$watermark_y	= $y - $main_img_obj_min_y;
				
				# fetch color information for both of our images
				$main_rgb = imagecolorsforindex( $main_img_obj, imagecolorat( $main_img_obj, $x, $y ) );
				
				# if our watermark has a non-transparent value at this pixel intersection
				# and we're still within the bounds of the watermark image
				if (	$watermark_x >= 0 && $watermark_x < $watermark_img_obj_w &&
							$watermark_y >= 0 && $watermark_y < $watermark_img_obj_h ) {
					$watermark_rbg = imagecolorsforindex( $watermark_img_obj, imagecolorat( $watermark_img_obj, $watermark_x, $watermark_y ) );
					
					# using image alpha, and user specified alpha, calculate average
					$watermark_alpha	= round( ( ( 127 - $watermark_rbg['alpha'] ) / 127 ), 2 );
					$watermark_alpha	= $watermark_alpha * $alpha_level;
				
					# calculate the color 'average' between the two - taking into account the specified alpha level
					$avg_red		= $this->_get_ave_color( $main_rgb['red'],		$watermark_rbg['red'],		$watermark_alpha );
					$avg_green	= $this->_get_ave_color( $main_rgb['green'],	$watermark_rbg['green'],	$watermark_alpha );
					$avg_blue		= $this->_get_ave_color( $main_rgb['blue'],	$watermark_rbg['blue'],		$watermark_alpha );

					# calculate a color index value using the average RGB values we've determined
					$return_color	= $this->_get_image_color( $return_img, $avg_red, $avg_green, $avg_blue );
					
				# if we're not dealing with an average color here, then let's just copy over the main color
				} else {
					$return_color	= imagecolorat( $main_img_obj, $x, $y );
					
				} # END if watermark
		
				# draw the appropriate color onto the return image
				imagesetpixel( $return_img, $x, $y, $return_color );
		
			} # END for each X pixel
		} # END for each Y pixel
			
		# return the resulting, watermarked image for display
		return $return_img;
	
	} # END create_watermark()
	
	# average two colors given an alpha
	function _get_ave_color( $color_a, $color_b, $alpha_level ) {
		return round( ( ( $color_a * ( 1 - $alpha_level ) ) + ( $color_b	* $alpha_level ) ) );
	} # END _get_ave_color()
		
	# return closest pallette-color match for RGB values
	function _get_image_color($im, $r, $g, $b) {
		$c=imagecolorexact($im, $r, $g, $b);
		if ($c>0) return $c;
		$c=imagecolorallocate($im, $r, $g, $b);
		if ($c>0) return $c;
		return imagecolorclosest($im, $r, $g, $b);
	} # EBD _get_image_color()

} # END watermark API
?>