<?php

    /*

     * desc: Resize Image(png, jpg, gif)

     * author: 十年后的卢哥哥(http://www.cnblogs.com/lurenjiashuo/)

     * date: 2014.11.13

     * base from: http://www.oschina.net/code/snippet_5189_2491

     */

    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;

        }

    }

?>

$resizeimage = new resizeimage($imgPath, $width, $height, $isCut, $savePath);

<?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");

?>