/**
     * desription 压缩图片
     * @param sting $imgsrc 图片路径
     * @param string $imgdst 压缩后保存路径
     */
    public function compressedImage($imgsrc, $imgdst) {
        list($width, $height, $type) = getimagesize($imgsrc);
       
        $new_width = $width;//压缩后的图片宽
        $new_height = $height;//压缩后的图片高
 
        if($width >= 600){
            $per = 600 / $width;//计算比例
            $new_width = $width * $per;
            $new_height = $height * $per;
        }
 
        switch ($type) {
            case 1:
                $giftype = check_gifcartoon($imgsrc);
                if ($giftype) {
                    header('Content-Type:image/gif');
                    $image_wp = imagecreatetruecolor($new_width, $new_height);
                    $image = imagecreatefromgif($imgsrc);
                    imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
                    //90代表的是质量、压缩图片容量大小
                    imagejpeg($image_wp, $imgdst, 90);
                    imagedestroy($image_wp);
                    imagedestroy($image);
                }
                break;
            case 2:
                header('Content-Type:image/jpeg');
                $image_wp = imagecreatetruecolor($new_width, $new_height);
                $image = imagecreatefromjpeg($imgsrc);
                imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
                //90代表的是质量、压缩图片容量大小
                imagejpeg($image_wp, $imgdst, 90);
                imagedestroy($image_wp);
                imagedestroy($image);
                break;
            case 3:
                header('Content-Type:image/png');
                $image_wp = imagecreatetruecolor($new_width, $new_height);
                $image = imagecreatefrompng($imgsrc);
                imagecopyresampled($image_wp, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
                //90代表的是质量、压缩图片容量大小
                imagejpeg($image_wp, $imgdst, 90);
                imagedestroy($image_wp);
                imagedestroy($image);
                break;
        }
    }

来源：https://www.cnblogs.com/fogwang/p/11459253.html