<?

$file = 'test.jpg';

header('Content-type: image/jpeg'); 
list($width, $height) = getimagesize($file); 
$source = imagecreatefromjpeg($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;
$g = ($rgb >> 8) & 0xFF;
$b = $rgb & 0xFF;

$gs = yiq($r,$g,$b);
imagesetpixel($bwimage,$x,$y,$palette[$gs]);
}
} 

imagejpeg($bwimage); 
?>