透過pngのリサイズ(ダメな例)

gistfile1.inc

<?php
/**
 * GD だけで png のリサイズしようとしたけどダメぽ
 *
 * @param string $in
 * @param string $out
 * @param int $per
 */
function resizePng($in, $out, $per) {
  $size = getimagesize($in);
  if ($size === false || $size['mime'] !== 'image/png') {
    return false;
  }

  $w    = $size[0];
  $h    = $size[1];
  $nw   = floor($w*$per/100);
  $nh   = floor($h*$per/100);

  $gd   = imagecreatefrompng($in);
  $gd_p = imagecreatetruecolor($nw, $nh);
  imagecopyresampled($gd_p, $gd, 0, 0, 0, 0, $nw, $nh, $w, $h);

  $idx = imagecolortransparent($gd);
  if ($idx >= 0) {
    $col = imagecolorsforindex($gd, $idx);
    $idx = imagecolorallocate($gd_p, $col['red'], $col['green'], $col['blue']);
    imagefill($gd_p, 0, 0, $idx);
    imagecolortransparent($gd_p, $idx);
  } else {
    imagealphablending($gd_p, false);
    $col = imagecolorallocatealpha($gd_p, 255, 255, 255, 127);
    imagefill($gd_p, 0, 0, $col);
    imagesavealpha($gd_p, true);
  }

  imagepng($gd_p, $out);
  imagedestroy($gd);
  imagedestroy($gd_p);
  
  return true;
}


resizePng('test1.png', 'test1_resize.png', 50);
resizePng('test2.png', 'test2_resize.png', 50);