支持png透明图片的php生成缩略图类分享

注：此功能依赖gd2图形库

最近要用php生成缩略图，在网上找了一下，发现了这篇文章：php生成图片缩略图

试用了一下后，发现有这样几个问题：

1、png图片生成的缩略图是jpg格式的

2、png图片生成的缩略图没有了透明（半透明）效果（填充了黑色背景）

3、代码语法比较老

因此，在这个版本的基础上简单修改优化了一下。

php生成缩略图类

<?php
  /*
   * desc: resize image(png, jpg, gif)
   * author: 十年后的卢哥哥
   * date: 2014.11.13
   */
  class resizeimage {
    //图片类型
    private $type;
    //实际宽度
    private $width;
    //实际高度
    private $height;
    //改变后的宽度
    private $resize_width;
    //改变后的高度
    private $resize_height;
    //是否裁图
    private $cut;
    //源图象
    private $srcimg;
    //目标图象地址
    private $dstimg;
    //临时创建的图象
    private $im;

    function __construct($imgpath, $width, $height, $iscut, $savepath) {
      $this->srcimg = $imgpath;
      $this->resize_width = $width;
      $this->resize_height = $height;
      $this->cut = $iscut;
      //图片的类型

      $this->type = strtolower(substr(strrchr($this->srcimg,"."),1));

      //初始化图象
      $this->initi_img();
      //目标图象地址
      $this -> dst_img($savepath);
      //--
      $this->width = imagesx($this->im);
      $this->height = imagesy($this->im);
      //生成图象
      $this->newimg();
      imagedestroy ($this->im);
    }

    private function newimg() {
      //改变后的图象的比例
      $resize_ratio = ($this->resize_width)/($this->resize_height);
      //实际图象的比例
      $ratio = ($this->width)/($this->height);
      if($this->cut) {
        //裁图
        $newimg = imagecreatetruecolor($this->resize_width,$this->resize_height);
        if($this->type=="png") {
          imagefill($newimg, 0, 0, imagecolorallocatealpha($newimg, 0, 0, 0, 127));
        }
        if($ratio>=$resize_ratio) {
          //高度优先
          imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width,$this->resize_height, (($this->height)*$resize_ratio), $this->height);
        } else {
          //宽度优先
          imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width, $this->resize_height, $this->width, (($this->width)/$resize_ratio));
        }
      } else {
        //不裁图
        if($ratio>=$resize_ratio) {
          $newimg = imagecreatetruecolor($this->resize_width,($this->resize_width)/$ratio);
          if($this->type=="png") {
            imagefill($newimg, 0, 0, imagecolorallocatealpha($newimg, 0, 0, 0, 127));
          }
          imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, $this->resize_width, ($this->resize_width)/$ratio, $this->width, $this->height);
        } else {
          $newimg = imagecreatetruecolor(($this->resize_height)*$ratio,$this->resize_height);
          if($this->type=="png") {
            imagefill($newimg, 0, 0, imagecolorallocatealpha($newimg, 0, 0, 0, 127));
          }
          imagecopyresampled($newimg, $this->im, 0, 0, 0, 0, ($this->resize_height)*$ratio, $this->resize_height, $this->width, $this->height);
        }
      }
      if($this->type=="png") {
        imagesavealpha($newimg, true);
        imagepng ($newimg,$this->dstimg);
      } else {
        imagejpeg ($newimg,$this->dstimg);
      }
    }

    //初始化图象
    private function initi_img() {
      if($this->type=="jpg") {
        $this->im = imagecreatefromjpeg($this->srcimg);
      }
      if($this->type=="gif") {
        $this->im = imagecreatefromgif($this->srcimg);
      }
      if($this->type=="png") {
        $this->im = imagecreatefrompng($this->srcimg);
      }
    }

    //图象目标地址
    private function dst_img($dstpath) {
      $full_length = strlen($this->srcimg);

      $type_length = strlen($this->type);
      $name_length = $full_length-$type_length;


      $name     = substr($this->srcimg,0,$name_length-1);
      $this->dstimg = $dstpath;
    }
  }
?>

使用

使用时，直接调用类的构造函数即可，构造函数如下：

$resizeimage = new resizeimage($imgpath, $width, $height, $iscut, $savepath);

参数
$imgpath：原图片地址

$width：缩略图宽

$height：缩略图高

$iscut：是否裁剪，bool值

$savepath：缩略图地址（可以跟原图片地址相同）

示例

<?php
  include "resizeimage.php";

  //jpg
  $jpgresize = new resizeimage("img/test_1920_1200.jpg", 320, 240, false, "img/test_320_240.jpg");

  //png
  $pngresize = new resizeimage("img/test_1024_746.png", 320, 240, false, "img/test_320_240.png");

?>

效果