gd library watermark in png image

Question

I'm trying to watermark images, but when the image is in PNG format, the watermark loses transparency.

$watermark = imagecreatefrompng('logo.png');

                $watermarkWidght = imagesx($watermark);
                $watermarkHeigth = imagesy($watermark);

                $image = imagecreatefrompng($path);

                $imageWidght = imagesx($imagenss);
                $imageHeigth = imagesy($imagenss);

                $positionX = ($imageWidght) - ($watermarkWidght);
                $positiony = ($imageHeigth) - ($watermarkHeigth);
imagealphablending($image , true); // set alpha
imagesavealpha($image , true);
 

                imagecopy($imagenss, $watermark, (int)$positionX, (int)$positiony,0,0, $watermarkWidght,$watermarkHeigth);
                ob_start();
                imagepng($imagenss);
                $ImageData=ob_get_contents();
                ob_end_clean();

PNG image with watermark

The watermark should maintain transparency when the background image is in .png format. When it comes to an image in .jpg format, the watermark maintains transparency.