Error in Converting GIF Image to Black & White

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I have a doubt in php.I wrote a php program to convert colour Images to

balck & white.It is working fine with JPEG files and PNG files.When it
comes to GIF files I am not getting the colour Image.I think I found
the reason of getting error.But I am not able to solve it
I am pasting the code which I wrote

The reason I think  is when I am extracting the RGB value from the
image,R and G will be zero everytime.But I am getting the value of B.
As a Result I am getting a Black Box instead of Black and white Image

$file    = 'logo2.gif';
header('Content-type: image/gif');
 $imgtype = "gif";
list($width, $height) = getimagesize($file);
$source = imagecreatefromgif($file);
$bwimage= imagecreate($width, $height);

for ($c=0;$c<256;$c++)
$palette[$c] = imagecolorallocate($bwimage,$c,$c,$c);


function yiq($r,$g,$b)
 return (($r*0.299)+($g*0.587)+($b*0.114));


for ($y=0;$y<$height;$y++)
for ($x=0;$x<$width;$x++)
$rgb = imagecolorat($source,$x,$y);
$r = ($rgb >> 16) & 0xFF;//error is here I am getting a value of zero
for $r and $g
$g = ($rgb >> 8) & 0xFF;//error getting the value zero everytime
$b = $rgb & 0xFF;//Here I am getting value

$gs = yiq($r,$g,$b);



Re: Error in Converting GIF Image to Black & White

Quoted text here. Click to load it

In the manual at it says:
Note: GIF support was removed from the GD library in Version 1.6, and added  
back in Version 2.0.28. This function is not available between these  

Check your GD version to see if it supports gif or not.

(I remember a time when gif was not supported. It's nice to see they've  
added it in the package again.)

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