php生成图片缩略图，支持png透明

James

　　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(http://www.iyunv.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;
}
}
?>
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