Wrong colors when merging images with PHP - php

Question

I want to get images ID's and creat from files a merged image according to the given ID's.
This code is called by ajax and return the image file name (which is the server time to prevent browser caching).
code:
if (isset($_REQUEST['items'])){
$req_items = $_REQUEST['items'];
} else {
$req_items = 'a';
}
$items = explode(',',$req_items);
$bg_img = imagecreatefrompng('bg.png');
for ($i=0; $i<count($items); $i++){
$main_img = $items[$i].'-large.png';
$image = imagecreatefrompng($main_img);
$image_tc = imagecreatetruecolor(300, 200);
imagecopy($image_tc,$image,0,0,0,0,300,200);
$black = imagecolorallocate($image_tc, 0, 0, 0);
imagecolortransparent($image_tc, $black);
$opacity = 100;
$bg_width = 300;
$bg_height = 200;
$dest_x = 0;//$image_size[0] - $bg_width - $padding;
$dest_y = 0;//$image_size[1] - $bg_height - $padding;
imagecopymerge($bg_img, $image_tc, $dest_x, $dest_y, 0, 0, $bg_width, $bg_height, $opacity)
;
}
$file = $_SERVER['REQUEST_TIME'].'.jpg';
imagejpeg($bg_img, $file, 100);
echo $file;
imagedestroy($bg_img);
imagedestroy($image);
die();
The images are shown exactly as I want but with wrong colors. I lately added the part with imagecreatetruecolor and imagecolortransparent, and still got wrong results.
I also saved the PNG itself on a 24 bit format and also later as 8 bit - not helping.
every ideas is very welcomed !
Thanks

Answer 1

After long time of trying... as always the solution was very simple:
Just make the background image a 24 bit as well.
So if someone is looking for a way to make layered transparent images this is the complete code:
<?php
if (isset($_REQUEST['items'])){
$req_items = $_REQUEST['items'];
} else {
$req_items = 'a';
}
$items = explode(',',$req_items);
$bg_img = imagecreatefrompng('bg.png');
$bg_tc = imagecreatetruecolor(300, 200);
imagecopy($bg_tc,$bg_img,0,0,0,0,300,200);
for ($i=0; $i<count($items); $i++){
$main_img = $items[$i].'-large.png';
$image = imagecreatefrompng($main_img);
$image_tc = imagecreatetruecolor(300, 200);
imagecopy($image_tc,$image,0,0,0,0,300,200);
$black = imagecolorallocate($image_tc, 0, 0, 0);
imagecolortransparent($image_tc, $black);
$opacity = 100;
$bg_width = 300;
$bg_height = 200;
$dest_x = 0;//$image_size[0] - $bg_width - $padding;
$dest_y = 0;//$image_size[1] - $bg_height - $padding;
imagecopymerge($bg_tc, $image_tc, $dest_x, $dest_y, 0, 0, $bg_width, $bg_height, $opacity);
}
$file = $_SERVER['REQUEST_TIME'].'.jpg';
imagejpeg($bg_tc, $file, 100);
echo $file;
imagedestroy($image);
imagedestroy($bg_img);
imagedestroy($bg_tc);
imagedestroy($image_tc);
die();
?>