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