JPEG conversion problem

[raffael3d]

I captured an image in Flash and then output it to the screen and JPEG via php.

unfortunately some colors are wrong and I get some weird artifacts:

on the right is the correct way it should look on, on the left is what I get after PHP to Jpeg

and here is my code. what am I doing wrong???

//If GD library is not installed, say sorry
	if(!function_exists("imagecreate")) die("Sorry, je hebt GD library nodig op de server om dit voorbeeld te kunnen bekijken");
	//Capture Post data
	$data = explode(",", $_POST['img']);
	$width = $_POST['width'];
	$height = $_POST['height'];
	//Allocate image
	$image=(function_exists("imagecreatetruecolor"))?imagecreatetruecolor( $width ,$height ):imagecreate( $width ,$height );
	$background = imagecolorallocate( $image ,0 , 0 , 0 );
	//Copy pixels
	$i = 0;
	for($x=0; $x<=$width; $x++){
		for($y=0; $y<=$height; $y++){
			$r = 255-hexdec("0X".substr( $data[$i] , 0 , 2 )); 
			$g = 255-hexdec("0x".substr( $data[$i] , 2 , 2 )); 
			$b = 255-hexdec("0x".substr( $data[$i++] , 4 , 2 ));
			$color =  ($r << 16) | ($g << 8) | $b; 
			imagesetpixel ( $image , $x , $y , $color );
		}
	}
	//Output image and clean
	header( "Content-type: image/jpeg" );
	ImageJPEG( $image );