Image resize with background color problem

[bbmak]

I try to resize an image to thumb with the background white. However, I only can fill half of the background. Anybody know why?

 

$img = imagecreatefromjpeg($target);
$tci = imagecreatetruecolor($w, $h);
imagecopyresampled($tci, $img, 0, 0, 0, 0, $w, $h, $w_orig, $h_orig);
$bg_color = imagecolorallocate ($tci, 255, 255, 255);
imagefill($tci, 0, 0, $bg_color);

 

a sample below. Anybody know why?