php png失真的原因及解决办法

<?php
    ob_clean();
    $bg = "image1.png";
    $image_1 = imagecreatefrompng($bg);
    $bgx = imagesx($image_1);
    $bgy = imagesy($image_1);
    //创建一个和背景图片一样大小的真彩色画布（ps：只有这样才能保证后面copy图片的时候不会失真）
    $bgimage = imagecreatetruecolor($bgx,$bgy);
    imagesavealpha($bgimage, true);//保持透明
    imagealphablending($bgimage, true);//混色模式
    $alpha = imagecolorallocatealpha($bgimage, 0, 0, 0, 127);//透明
    imagefill($bgimage, 0, 0, $alpha);
    //copy背景图片
    imagecopyresampled($bgimage,$image_1,0,0,0,0,$bgx,$bgy,$bgx,$bgy);
    $fontcolor = imagecolorallocate($bgimage,0x33,0x33,0x33);
    $image_2 = imagecreatefrompng( "image2.png");
    //合成图片2
    imagecopyresampled($bgimage, $image_2, 100, 100, 0, 0, 40, 40, imagesx($image_2) , imagesy($image_2));
    //文字
    $textlen = mb_strlen($text1);
    $fontsize  = 20;
    $fontwidth = imagefontwidth($fontsize)*3;//不知为什么，实测如此
    $textwidth = $fontwidth * mb_strlen($text1);
    $textx = ceil ( ($bgx - $textwidth) / 2 );
    imagettftext($bgimage, $fontsize, 0, $textx, 450, $fontcolor, $font , $text1);
    $result = imagepng($bgimage,"newimage.png");
    imagedestroy($bgimage);
    imagedestroy($qrcode);

$ni = imagecreatetruecolor($tow,$toh); //创建真彩色图片
$bg_x = (($tow-$ftow)/2);
$bg_y = (($toh-$ftoh)/2);
$color=imagecolorallocate($ni,255,255,255); //创建颜色
imagefill($ni, 0, 0, $color); //设置白底
imagecopy($ni,$tm,$bg_x,$bg_y,0,0,$ftow,$ftoh); //合并图片
imagedestroy($tm);