How to add gray translucent effect to pictures in PHP, _PHP tutorial

/*php adds gray transparency effect to the image*/
$imfile = './0.jpg';//Original image
$origim = imagecreatefromjpeg($imfile);//Create a new image from a JPEG file or URL

$w=imagesx($origim);//Width of original image
$h=imagesy($origim);//Height of original image

$newimg = imagecreatetruecolor($w, $h);//Returns an image identifier, representing a black image of size x_size and y_size. imagecreatetruecolor// 

$color=imagecolorallocatealpha($newimg,0,0,0,75);//Assign color + alpha to an image; Same as imagecolorallocate(), but with an additional transparency parameter alpha, whose value ranges from 0 to 127 . 0 means completely opaque, 127 means completely transparent.

imagecolortransparent($newimg,$color);//Define a color as a transparent color

imagefill($newimg,0,0,$color);//Area filling;resource $image, int $x, int $y, int $color

imagecopy($origim,$newimg, 0,0, 0, 0,$w, $h);//Copy part of the image; the coordinates in the src_im image start from src_x, src_y, the width is src_w, and the height is part of src_h Copy to the positions of coordinates dst_x and dst_y in the dst_im image.

imagejpeg($origim, './2.jpg');//Output the image to the browser or file. ;resource $image [, string $filename [, int $quality ]]
?>