php如何生成持透明png的图片缩略图

原创: 2016-08-08 09:33:30 925浏览

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.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);
        } privatefunction 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,$this->dstimg);
            }
        } //初始化图象privatefunction initi_img() { if($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privatefunction 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"); ?>