如何改进我的PHP图像缩放器，以支持alpha png和透明GIF

Question

I use this function to resize images but i end up with ugly creepy image with a black background if it's a transparent GIF or PNG with alpha, however it works perfectly for jpg and normal png.

function cropImage($nw, $nh, $source, $stype, $dest) {
     $size = getimagesize($source);
     $w = $size[0];
      $h = $size[1];

      switch($stype) {
          case 'gif':
          $simg = imagecreatefromgif($source);
          break;
          case 'jpg':
          $simg = imagecreatefromjpeg($source);
          break;
          case 'png':
          $simg = imagecreatefrompng($source);
          break;
      }


     $dimg = imagecreatetruecolor($nw, $nh);

     switch ($stype)
    {
         case "png":

     imagealphablending( $dimg, false );
     imagesavealpha( $dimg, true );
     $transparent = imagecolorallocatealpha($dimg, 255, 255, 255, 127);
     imagefilledrectangle($dimg, 0,  0, $nw, $nh,  $transparent);

    break;
case "gif":
    // integer representation of the color black (rgb: 0,0,0)
    $background = imagecolorallocate($simg, 0, 0, 0);
    // removing the black from the placeholder
    imagecolortransparent($simg, $background);

    break;
     }



      $wm = $w/$nw;
      $hm = $h/$nh;
      $h_height = $nh/2;
      $w_height = $nw/2;

      if($w> $h) {
          $adjusted_width = $w / $hm;
          $half_width = $adjusted_width / 2;
          $int_width = $half_width - $w_height;
          imagecopyresampled($dimg,$simg,-$int_width,0,0,0,$adjusted_width,$nh,$w,$h);
      } elseif(($w <$h) || ($w == $h)) {
          $adjusted_height = $h / $wm;
          $half_height = $adjusted_height / 2;
          $int_height = $half_height - $h_height;

     imagecopyresampled($dimg,$simg,0,-$int_height,0,0,$nw,$adjusted_height,$w,$h);
      } else {
          imagecopyresampled($dimg,$simg,0,0,0,0,$nw,$nh,$w,$h);
      }

      imagejpeg($dimg,$dest,100);
     }

Example : cropImage("300","200","original.png","png","new.png");

I use php 5.3.2 and the GD library bundled (2.0.34 compatible)

How to make it support transparency? i've added imagealphablending() and imagesavealpha but it didn't work. Or atlast is there any similar good classes?

Thanks

Answer 1

The ugly black background disappears if you output the image to png. So here are the two alternative solutions, both tested:

1. If you can store the thumbnail as png, just do it: change imagejpeg($dimg,$dest,100); to imagepng($dimg,$dest);

2. If it's important to store it as jpeg, remove the lines imagealphablending( $dimg, false ); and imagesavealpha( $dimg, true ); -- the default values of true and false, respectively, will provide the desired effect. Disabling alpha blending only makes sense if the result image also has an alpha channel.