PHP remove a section of image leaving a transparent space - php

Question

I have an transparent image with a bar through the middle...
http://i66.tinypic.com/2zyeg4h.png
Using php I would like to remove the middle part on the bar, leaving a transparent space in the middle of the bar. I try this code...
$im = imagecreatefrompng('****root****/image.png');
//make a yellow box
$transparent = imagecolorallocate($im, 255, 255, 0);
//make the yellow box transparent
imagecolortransparent($im, $transparent);
imagefilledrectangle($im, 200, 115, 300, 137, $transparent);
imagealphablending($im, false);
imagesavealpha($im, true);
header ('Content-Type: image/png');
imagepng($im);
$save = "****root****/test.png";
imagepng($im, $save);
imagedestroy($im);
?>
But the output image has the rectangle retain the yellow colour, rather than turn it transparent.
http://i67.tinypic.com/1ny6j4.png
Where am I going wrong? If I remove...
imagealphablending($im, false);
imagesavealpha($im, true);
I get the transparent box in the center (in the browser), but the rest of the image loses it's transparency and has a white background instead, also when I download that image and open in a photo editor, the transparency box in the center is gone. I have GD libraries set up on my server.

Answer 1

You need to use the gd function imagecolorallocatealpha to create a transparent color.
You could generate the whole image with PHP.
e.g.
<?php
// generate empty image
$image = imagecreate(500, 262);
// define black
$black = imagecolorallocate($image, 0, 0, 0);
// create left part of the bar
imagefilledrectangle($image, 0, 110, 200, 162, $black);
// create right part of the bar
imagefilledrectangle($image, 300, 110, 500, 162, $black);
// save image
imagepng($image, 'outimage.png');
If you want to stick with an existing image
<?php
// generate empty image
$image = imagecreatefrompng('input.png');
// define transparent
$transparent = imagecolorallocatealpha($image, 255, 255, 255, 127);
// create the transparent area
imagefilledrectangle($image, 200, 110, 300, 162, $transparent);
// save image
imagepng($image, 'output.png');
input.png
output.png
You don't need to send a header if you're not submitting the image as a result to a browser.
e.g.
header('Content-Type: image/png');
imagepng($image);
Would display the image in the requesting browser rather than saving it to a file.