PHP watermarking - php

Question

i am using this code to create watermark.
$image = '1.jpg';
$overlay = 'stamp.png';
$opacity = "20";
if (!file_exists($image)) {
die("Image does not exist.");
}
// Set offset from bottom-right corner
$w_offset = 0;
$h_offset = 100;
$extension = strtolower(substr($image, strrpos($image, ".") + 1));
// Load image from file
switch ($extension)
{
case 'jpg':
$background = imagecreatefromjpeg($image);
break;
case 'jpeg':
$background = imagecreatefromjpeg($image);
break;
case 'png':
$background = imagecreatefrompng($image);
break;
case 'gif':
$background = imagecreatefromgif($image);
break;
default:
die("Image is of unsupported type.");
}
// Find base image size
$swidth = imagesx($background);
$sheight = imagesy($background);
// Turn on alpha blending
imagealphablending($background, true);
// Create overlay image
$overlay = imagecreatefrompng($overlay);
// Get the size of overlay
$owidth = imagesx($overlay);
$oheight = imagesy($overlay);
// Overlay watermark
imagecopymerge($background, $overlay, $swidth - $owidth - $w_offset, $sheight - $oheight - $h_offset, 0, 0, $owidth, $oheight, $opacity);
imagejpeg($background,$image);
// Destroy the images
imagedestroy($background);
imagedestroy($overlay);
the png image contains a text with all other region as transparent.
but when i execute this code , it applys the png over jpg, but the transparecy is not maintained of the png. it shows in a box.
how can i acheive that . ie if a png contains transaparent part , it should show the below image in that part....?

Answer 1

replacing imagecopymerge with imagecopy solved the issue. here is the new code
function watermark($image){
$overlay = '../../../photos/photosets/stamp.png';
$opacity = "20";
if (!file_exists($image)) {
die("Image does not exist.");
}
// Set offset from bottom-right corner
$w_offset = 0;
$h_offset = 100;
$extension = strtolower(substr($image, strrpos($image, ".") + 1));
// Load image from file
switch ($extension)
{
case 'jpg':
$background = imagecreatefromjpeg($image);
break;
case 'jpeg':
$background = imagecreatefromjpeg($image);
break;
case 'png':
$background = imagecreatefrompng($image);
break;
case 'gif':
$background = imagecreatefromgif($image);
break;
default:
die("Image is of unsupported type.");
}
// Find base image size
$swidth = imagesx($background);
$sheight = imagesy($background);
// Turn on alpha blending
imagealphablending($background, true);
// Create overlay image
//$overlay = imagecreatefrompng($overlay);
// Get the size of overlay
$owidth = imagesx($overlay);
$oheight = imagesy($overlay);
$photo = imagecreatefromjpeg($image);
$watermark = imagecreatefrompng($overlay);
// This is the key. Without ImageAlphaBlending on, the PNG won't render correctly.
imagealphablending($photo, true);
// Copy the watermark onto the master, $offset px from the bottom right corner.
$offset = 10;
imagecopy($photo, $watermark, imagesx($photo) - imagesx($watermark) - $offset, imagesy($photo) - imagesy($watermark) - $offset, 0, 0, imagesx($watermark), imagesy($watermark));
// Output to the browser
header("Content-Type: image/jpeg");
imagejpeg($photo,$image);
// Overlay watermark
// Destroy the images
imagedestroy($background);
imagedestroy($overlay);
}

Answer 2

The jpg format doesn't support transparency, so conceptually you will have to:
grab the pixels from the larger image (the jpeg) and put them into a buffer
grab the non-transparent pixels from the smaller image (the watermark) and move them into that buffer, applying the alpha along the way
You probably want to let a library do this. I like ImageMagick, especially since it's built in to php... here's an example of how to use it for this purpose from PHP:
// Let's read the images.
$glasses = new Imagick();
if (FALSE === $glasses->readImage($dir . '/glasses.png'))
{
throw new Exception();
}
$face = new Imagick();
if (FALSE === $face->readImage($dir . '/face.jpg'))
{
throw new Exception();
}
// Let's put the glasses on (10 pixels from left, 20 pixels from top of face).
$face->compositeImage($glasses, Imagick::COMPOSITE_DEFAULT, 10, 20);
And here's the link to the PHP manual page for ImageMagick::compositeImage (from which the above example came).

Answer 3

Have you tried using imagecopyresampled()?
http://php.net/manual/en/function.imagecopyresampled.php