Posted by retheeshnewage on 07/31/06 05:16

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);
imagesetpixel($bwimage,$x,$y,$palette[$gs]);



}
}


imagegif($bwimage);

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