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<?php
class watermark{
# given two images, return a blended watermarked image
function create_watermark( $main_img_obj, $watermark_img_obj, $alpha_level = 100 ) {
$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 center position coordinates
$main_img_obj_min_x = floor( ( $main_img_obj_w / 1 ) - ( $watermark_img_obj_w / 1 ) );
$main_img_obj_max_x = ceil( ( $main_img_obj_w / 1 ) + ( $watermark_img_obj_w / 1 ) );
$main_img_obj_min_y = floor( ( $main_img_obj_h / 1 ) - ( $watermark_img_obj_h / 1 ) );
$main_img_obj_max_y = ceil( ( $main_img_obj_h / 1 ) + ( $watermark_img_obj_h / 1 ) );
# create new image to hold merged changes
$return_img = imagecreatetruecolor( $main_img_obj_w, $main_img_obj_h );
# walk through main image
for( $y = 0; $y < $main_img_obj_h; $y++ ) {
for( $x = 0; $x < $main_img_obj_w; $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!=-1) return $c;
$c=imagecolorallocate($im, $r, $g, $b);
if ($c!=-1) return $c;
return imagecolorclosest($im, $r, $g, $b);
} # EBD _get_image_color()
} # END watermark API
?>