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Friday, February 6, 2009

Putting watermark on an Image

While working on a project, I found this useful class for achieving watermarking task easily. Here is the code.

Class:

class watermark
{
var $img;
function create_watermark( $main_img_obj, $watermark_img_obj, $alpha_level = 100 )
{
$alpha_level /= 100;
$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 );
$main_img_obj_min_x=10;
$main_img_obj_max_x=10;
$main_img_obj_min_y=10;
$main_img_obj_max_y=10;
$return_img = imagecreatetruecolor( $main_img_obj_w, $main_img_obj_h );

for( $y = 0; $y < $main_img_obj_h; $y++ )
{
for( $x = 0; $x < $main_img_obj_w; $x++ )
{
$return_color = NULL;
$watermark_x = $x - $main_img_obj_min_x;
$watermark_y = $y - $main_img_obj_min_y;
$main_rgb = imagecolorsforindex( $main_img_obj,
imagecolorat( $main_img_obj, $x, $y ) );
if ($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 ) );
$watermark_alpha = round( ( ( 127 - $watermark_rbg['alpha'] ) / 127 ), 2 );
$watermark_alpha = $watermark_alpha * $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 );
$return_color = $this->_get_image_color( $return_img, $avg_red, $avg_green, $avg_blue );
}
else
{
$return_color = imagecolorat( $main_img_obj, $x, $y );
}
imagesetpixel( $return_img, $x, $y, $return_color );
}
}
$this->img = $return_img;
}
function _get_ave_color( $color_a, $color_b, $alpha_level )
{
return round((($color_a*(1-$alpha_level))+($color_b*$alpha_level)));
}
function _get_image_color($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, $b);
}
function write($target)
{
imagejpeg($this->img, $target, 100);
}
}

Usage:

$watermark = new watermark();
$main_img_obj = imagecreatefromjpeg("image.jpg"); //Image which you want to put watermark on
$watermark_img_obj = imagecreatefrompng("logo.png"); //Watermark image (PNG file)
$watermark->create_watermark( $main_img_obj, $watermark_img_obj, 100 );
$watermark->write("image_with_watermark.jpg"); //Output Image

It takes image.jpg, puts logo.png on it as watermark and saves it as a new image file named image_with_watermark.jpg. Thats it!

Happy Coding :)

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