imagepng and imagegif - php

Question

I need some help about PHP GD. Here is my piece of code.
header("Content-type: image/gif");
$image = imagecreatetruecolor(550, 20);
imagealphablending($image, false);
$col=imagecolorallocatealpha($image,255,255,255,127);
$black = imagecolorallocate($image, 0, 0, 0);
imagefilledrectangle($image,0,0,550,20,$col);
imagealphablending($image, true);
$font_path = 'font/arial.ttf';
imagettftext($image, 9, 0, 16, 13, $black, $font_path, $lastlisten);
imagesavealpha($image, true);
imagepng($image);
The problem is when I use imagepng, it can show the png just fine like this.
But if I use imagegif instead, it will become this.
I did tried using different header for gif and png. The result for imagegif is still the same.
The question is how do I make in order to display GIF version properly? Thanks you

Answer 1

GIF image supports a maximum of 256 colors. Most importantly, it only supports index transparency: a pixel can be 100% opaque or 100% transparent.
PNG on the other hand supports true (millions of) color images and supports alpha channel transparency. That means a pixel can be 100% opaque, 100% transparent or anything in between.
The PNG image you mentioned probably has its edges partially transparent therefore the browser can easily blend those pixels with the background color giving a smooth effect. PNG is a better choice.

Answer 2

First problem : your characters are ugly: that's because you need to set a palette with less colors when using imagecreatetruecolor.
$image = imagecreatetruecolor(550, 20);
imagetruecolortopalette($image, true, 256);
should solve this problem.
Second problem : there is no transparency.
As you can see on PHP manual,
imagesavealpha() sets the flag to attempt to save full alpha channel
information (as opposed to single-color transparency) when saving PNG
images.
This function does not work with GIF files.
You can use imagecolortransparent instead but this will not be perfect because fonts has anti-aliasing to make their border sweeter.
Here is my code:
<?php
$lastlisten = "test test test test test test";
error_reporting(E_ALL);
header("Content-type: image/gif");
$image = imagecreatetruecolor(550, 20);
imagetruecolortopalette($image, true, 256);
$transparent=imagecolorallocatealpha($image,255,255,255,127);
imagecolortransparent( $image, $transparent);
imagefilledrectangle($image,0,0,550,20,$transparent);
$black = imagecolorallocate($image, 0, 0, 0);
$font_path = dirname(__FILE__) . '/font.ttf';
imagettftext($image, 9, 0, 16, 13, $black, $font_path, $lastlisten);
imagegif($image);
Result here
Hope this helps.