php压缩图片

注意alpha通道的的拷贝 不然png图片会有问题

<?php


namespace App\Models\pub;

/**
 * 图片压缩类：通过缩放来压缩。
 * 如果要保持源图比例，把参数$percent保持为即可。
 * 即使原比例压缩，也可大幅度缩小。数码相机M图片。也可以缩为KB左右。如果缩小比例，则体积会更小。
 *
 * 结果：可保存、可直接显示。
 */
class ImgCompress
{
    private $src;
    private $image;
    private $imageinfo;
    private $percent;
    const PERCENT = 1;
   /**
    * 图片压缩
    * @param $src string 源图
    * @param float $percent 压缩比例
    */
   public function __construct($src, $percent)
   {
       $this->src = $src;
       $this->percent = $percent;
   }

    /** 高清压缩图片
     * @param string $saveName 提供图片名（可不带扩展名，用源图扩展名）用于保存。或不提供文件名直接显示
     */
    public function compressImg($saveName='')
    {
        $this->_openImage();
        if(!empty($saveName)) $this->_saveImage($saveName); //保存
        else $this->_showImage();
    }
    /**
     * 内部：打开图片
     */
    private function _openImage()
    {
        list($width, $height, $type, $attr) = getimagesize($this->src);
        $this->imageinfo = array(
            'width'=>$width,
            'height'=>$height,
            'type'=>image_type_to_extension($type,false),
            'attr'=>$attr
        );
        $fun = "imagecreatefrom".$this->imageinfo['type'];
        $this->image = $fun($this->src);
        $this->_thumpImage();
    }
    /**
     * 内部：操作图片
     */
    private function _thumpImage()
    {
        $new_width = $this->imageinfo['width'] * $this->percent;
        $new_height = $this->imageinfo['height'] * $this->percent;
        $image_thump = imagecreatetruecolor($new_width,$new_height);
        $alpha = imagecolorallocatealpha($image_thump, 0, 0, 0, 127);
        imagefill($image_thump, 0, 0, $alpha);
        //$color = imagecolorallocate($image_thump,255,255,255);
        //imagecolortransparent($image_thump,$color);
        //imagefill($image_thump,0,0,$color);
        //将原图复制带图片载体上面，并且按照一定比例压缩,极大的保持了清晰度
        imagecopyresampled($image_thump,$this->image,0,0,0,0,$new_width,$new_height,$this->imageinfo['width'],$this->imageinfo['height']);
        imagedestroy($this->image);
        $this->image = $image_thump;
    }
    /**
     * 输出图片:保存图片则用saveImage()
     */
    private function _showImage()
    {
        header('Content-Type: image/'.$this->imageinfo['type']);
        $funcs = "image".$this->imageinfo['type'];
        $funcs($this->image);
    }
    /**
     * 保存图片到硬盘：
     * @param string $dstImgName 、可指定字符串不带后缀的名称，使用源图扩展名 。、直接指定目标图片名带扩展名。
     */
    private function _saveImage($dstImgName)
    {
        if(empty($dstImgName)) return false;
        $allowImgs = ['.jpg', '.jpeg', '.png', '.bmp', '.wbmp','.gif'];  //如果目标图片名有后缀就用目标图片扩展名 后缀，如果没有，则用源图的扩展名
        $dstExt = strrchr($dstImgName ,".");
        $sourseExt = strrchr($this->src ,".");
        if(!empty($dstExt)) $dstExt =strtolower($dstExt);
        if(!empty($sourseExt)) $sourseExt =strtolower($sourseExt);
        //有指定目标名扩展名
        if(!empty($dstExt) && in_array($dstExt,$allowImgs)){
            $dstName = $dstImgName;
        }elseif(!empty($sourseExt) && in_array($sourseExt,$allowImgs)){
            $dstName = $dstImgName.$sourseExt;
        }else{
            $dstName = $dstImgName.$this->imageinfo['type'];
        }
        $funcs = "image".$this->imageinfo['type'];
        imagesavealpha($this->image, true);
        $funcs($this->image,$dstName);
    }

    public static function getImagetype($filename)
    {
        $file = fopen($filename, 'rb');
        $bin  = fread($file, 2); //只读2字节
        fclose($file);
        $strInfo  = @unpack('C2chars', $bin);
        $typeCode = intval($strInfo['chars1'].$strInfo['chars2']);
        // dd($typeCode);
        $fileType = '';
        switch ($typeCode) {
            case 255216:
                $fileType = 'jpg';
                break;
            case 7173:
                $fileType = 'gif';
                break;
            case 6677:
                $fileType = 'bmp';
                break;
            case 13780:
                $fileType = 'png';
                break;
            default:
                $fileType = '只能上传图片类型格式';
        }
        // if ($strInfo['chars1']=='-1' AND $strInfo['chars2']=='-40' ) return 'jpg';
        // if ($strInfo['chars1']=='-119' AND $strInfo['chars2']=='80' ) return 'png';
        if(!in_array($fileType, ['jpg', 'jpeg', 'gif', 'bmp', 'png'])) {
            return false;
        }
        return true;
    }

    /**
     * 销毁图片
     */
    public function __destruct(){
        imagedestroy($this->image);
    }
}