PHP example code for reducing png images without losing transparent color

imagecolorallocatealpha //Assign color + alpha
imagesavealpha //Set to save complete alpha channel information when saving png images

Full code:

//Get the source image gd image identifier
$srcImg = imagecreatefrompng('./src.png');
$srcWidth = imagesx($srcImg);
$srcHeight = imagesy ($srcImg);
//Create a new image bbs.it-home.org
$newWidth = round($srcWidth / 2);
$newHeight = round($srcHeight / 2);
$newImg = imagecreatetruecolor($newWidth , $newHeight);
//Assign color + alpha, fill the color onto the new image
$alpha = imagecolorallocatealpha($newImg, 0, 0, 0, 127);
imagefill($newImg, 0, 0, $alpha );
//Copy the source image to the new image, and set it to save the complete alpha channel information when saving the PNG image
imagecopyresampled($newImg, $srcImg, 0, 0, 0, 0, $newWidth, $newHeight, $srcWidth, $srcHeight);
imagesavealpha($newImg, true);
imagepng($newImg, './dst.png');