使用PHP将图像旋转45度时如何避免黑色背景？

<?
$image = "130.jpg";
$degrees = 25;
for($i=0;$i<count($data);$i++){
    $ext = "";
    $extarr = "";
    $extarr = explode(".",$data[$i]['name']);
    $ext = array_pop($extarr);
    if($ext == "png"){
        $rotate = imagecreatefrompng("images/".$data[$i]['name']);
        $transColor = imagecolorallocatealpha($rotate,255,270);
        $watermark1[$i] = imagerotate($rotate,((360-$degrees)%360),$transColor);
    }
}

function imagecopymerge_alpha($dst_im,$src_im,$dst_x,$dst_y,$src_x,$src_y,$src_w,$src_h,$opct){
    $w = imagesx($src_im);
    $h = imagesy($src_im);
    $cut = imagecreatetruecolor($src_w,$src_h);
    imagecopy($cut,$dst_im,$src_h);
    imagecopymerge($dst_im,$cut,(100 - $opct));
}


for($i=0; $i<count($watermark1); $i++){
    if($i == 0) imagecopymerge_alpha($image,$watermark1[$i],$dest_x,$dest_y,$watermark_width,$watermark_height,$opacity);
    else imagecopymerge_alpha($image,($i*$dest_x)*3,($i*$dest_y)*15,$opacity);
    imagedestroy($watermark1[$i]);
}
header("content-type: image/png");
imagepng($image);
imagedestroy($image);
?>

此外,您的水印图像是否具有Alpha通道或者它们是否完全不透明？