Description:
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I have problem with imagepng;

"imagepng()" This code shows broken image on browser, but its working fine to save 
the image on local disk. for example: imagepng($image,"a.png"); is working but I 
don't want to save this file.

Test script:
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        $image = imagecreatetruecolor(200, 400) or die("a");
        $bg = imagecolorallocate($image, 255, 255, 255) or die("d");

        imagestring($image, 12, 10, 100, "Hello", $bg) or die("b");
        header('Content-type: image/png');
        imagepng($image) or die("c");


Expected result:
----------------
"Hello" Image on Browser

Actual result:
--------------
Broken Image on Chrome
and 
Firefox output:
The image "http://localhost/Test/index.php" cannot be displayed because it 
contains errors.