使用 SimpleImage.php 类调整 PNG 透明度

Question

我正在使用 SimpleImage.php 类的修改版本：http://www.white-hat-web-design.co.uk/articles/php-image-resizing.php

我在 phpfreaks (http://www.phpfreaks.com/forums/index.php?topic=301811.0) 上找到的编辑，但是当我使用时，png 会调整大小但透明度是黑色的。

我这样打电话：

 $max_width = 200; // set a max width
 $max_height = 150; // set a max height
 if($imgW > $imgH){ // width is greater
      // resize to width up to max
      if($imgW > $max_width) $image->resizeToWidth($max_width);
 }
 else { // height is greater
      // resize to height up to max
      if($imgH > $max_height) $image->resizeToHeight($max_height);
 }

 $image->save($_SERVER['DOCUMENT_ROOT']."/path/" . $new_filename);

我不确定缺少什么。任何帮助表示赞赏...

class SimpleImage {
     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=75, $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( $image_type == IMAGETYPE_PNG ) {
            imageAlphaBlending($this->image, true);
            imageSaveAlpha($this->image, true);
            imagepng($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) {

        // ADDED CODE IS HERE - NOT SURE WHY IT DOESN'T WORK FOR PNG

        // Setup new image
        $new_image = imagecreatetruecolor($width, $height);
        // These parameters are required for handling PNG files.
        imagealphablending($new_image, false);
        imagesavealpha($new_image,true);
        $transparent = imagecolorallocatealpha($new_image, 255, 255, 255, 127);
        imagefilledrectangle($new_image, 0, 0, $width, $height, $transparent);
        // Resize image
        imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());
        $this->image = $new_image;
    }
}

Answer 1

现在透明度适用于 PNG 但不适用于 gif。以下是对特定功能的编辑，以防对其他人有所帮助：

保存功能：

function save($filename, $image_type=IMAGETYPE_JPEG, $compression=75, $permissions=null) {

   // do this or they'll all go to jpeg
   $image_type=$this->image_type;

  if( $image_type == IMAGETYPE_JPEG ) {
     imagejpeg($this->image,$filename,$compression);
  } elseif( $image_type == IMAGETYPE_GIF ) {
     imagegif($this->image,$filename);  
  } elseif( $image_type == IMAGETYPE_PNG ) {
    // need this for transparent png to work          
    imagealphablending($this->image, false);
    imagesavealpha($this->image,true);
    imagepng($this->image,$filename);
  }   
  if( $permissions != null) {
     chmod($filename,$permissions);
  }

}

调整大小功能

 function resize($width,$height,$forcesize='n') {

  /* optional. if file is smaller, do not resize. */
  if ($forcesize == 'n') {
      if ($width > $this->getWidth() && $height > $this->getHeight()){
          $width = $this->getWidth();
          $height = $this->getHeight();
      }
  }

  $new_image = imagecreatetruecolor($width, $height);
  /* Check if this image is PNG or GIF, then set if Transparent*/  
  if(($this->image_type == IMAGETYPE_GIF) || ($this->image_type==IMAGETYPE_PNG)){
      imagealphablending($new_image, false);
      imagesavealpha($new_image,true);
      $transparent = imagecolorallocatealpha($new_image, 255, 255, 255, 127);
      imagefilledrectangle($new_image, 0, 0, $width, $height, $transparent);
  }
  imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());

  $this->image = $new_image;   

}

Answer 2

imagecreatetruecolor() 函数不适用于 GIF。请改用imagecreate 方法：

if($this->image_type == IMAGETYPE_GIF){
    $new_image = imagecreate( $Width, $Height ); // for gif files
} else{
    $new_image = imagecreatetruecolor($Width, $Height); // for all other files
}

Answer 3

我自己已经很久没有玩过GD了（我更喜欢Imagemagick），但是你可以尝试在复制之前将alpha设置为源图像：

...
// ADDED CODE IS HERE ..
imagealphablending($this->image, true);
...

HTH。

Answer 4

我在https://stackoverflow.com/a/6401135/262462 中做了同样的事情，但编辑了这部分

function save($filename, $image_type=IMAGETYPE_JPEG, $compression=75, $permissions=null) {

// do this or they'll all go to jpeg
$image_type=$this->image_type;

到这里

function save($filename, $image_type="original", $compression=75, $permissions=null) {

    if ($image_type=="original")
        $image_type=$this->image_type;