如何在使用PHP调整大小时保持PNG的透明背景？

Question

我在使用PHP调整图片大小时遇到​​问题,特别是对于具有透明背景的PNG文件,而不是保持透明背景,它会变成黑色背景.我怎样才能解决这个问题？

这是用于调整大小的脚本:

<?php         
class resize{

   var $image;
   var $image_type;

   function load($filename) {

      $image_info = getimagesize($filename);
      $this->image_type = $image_info[2];
      if( $this->image_type == IMAGETYPE_JPEG ) {

         $this->image = imagecreatefromjpeg($filename);
      } elseif( $this->image_type == IMAGETYPE_GIF ) {

         $this->image = imagecreatefromgif($filename);
      } elseif( $this->image_type == IMAGETYPE_PNG ) {

         $this->image = imagecreatefrompng($filename);
      }
   }
   function save($filename, $image_type=IMAGETYPE_JPEG, $compression=85, $permissions=null) {

      if( $image_type == IMAGETYPE_JPEG ) {
         imagejpeg($this->image,$filename,$compression);
      } elseif( $image_type == IMAGETYPE_GIF ) {

         imagegif($this->image,$filename);
      } elseif( $image_type == IMAGETYPE_PNG ) {




         imagepng($this->image,$filename);
      }
      if( $permissions != null) {

         chmod($filename,$permissions);
      }
   }
   function output($image_type=IMAGETYPE_JPEG) {

      if( $image_type == IMAGETYPE_JPEG ) {
         imagejpeg($this->image);
      } elseif( $image_type == IMAGETYPE_GIF ) {

         imagegif($this->image);
      } elseif( $image_type == IMAGETYPE_PNG ) {

         imagepng($this->image);
      }
   }
   function getWidth() {

      return imagesx($this->image);
   }
   function getHeight() {

      return imagesy($this->image);
   }
   function resizeToHeight($height) {

      $ratio = $height / $this->getHeight();
      $width = $this->getWidth() * $ratio;
      $this->resize($width,$height);
   }

   function resizeToWidth($width) {
      $ratio = $width / $this->getWidth();
      $height = $this->getheight() * $ratio;
      $this->resize($width,$height);
   }

   function scale($scale) {
      $width = $this->getWidth() * $scale/100;
      $height = $this->getheight() * $scale/100;
      $this->resize($width,$height);
   }

   function resize($width,$height) {

      $new_image = imagecreatetruecolor($width, $height);   
      imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());
      $this->image = $new_image;
   }      

}
?>

这就是我所说的:

$picture_directory="images/" . $_FILES["file"]["name"];

    include('arqinc/resizing.php');
    $image = new resize();
    $image->load($picture_directory);
    $image->resize(660,780);
    $image->save($picture_directory);

编辑:

香港专业教育学院改变了我的调整大小功能:

function resize($width,$height) {

      $new_image = imagecreatetruecolor($width, $height);
      $transparent=imagefill($new_image, 0, 0, imagecolorallocatealpha($new_image, 255, 255, 255, 127));
      imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());
      $this->image = $new_image;
   }  

但现在它使背景保持白色,而不是透明.

编辑2:

解决了,这个调整大小的功能被打破了,这个功能完美无缺:

http://mediumexposure.com/smart-image-resizing-while-preserving-transparency-php-and-gd-library/

感谢 Tahir Yasin将其链接起来:D

Answer 1

我发现另一个帖子有相同的问题,根据该帖子,下面的代码可以用来保持透明度.

imagealphablending( $targetImage, false );
imagesavealpha( $targetImage, true );

参考:使用PHP的GDlib imagecopyresampled时,是否可以保留PNG图像透明度？

如果有帮助,请投票.:)