Generate thumbnails

1, get the width and height of the uploaded avatar

<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2018/2/28 0028
 * Time: 下午 1:18
 */
header('Content-type:text/html;charset=utf-8');
$info=array('id'=>1,'name'=>'张三');
//接收并处理上传图像
if(!empty($_FILES['pic'])){
    $pic_info=$_FILES['pic'];
    //获取图片大小
    $image_info=getimagesize($pic_info['tmp_name']);
    echo '<pre>';
    print_r($image_info);
    echo '</pre>';
    $width=$image_info[0];
    $height=$image_info[1];
}
?>
<form action="" method="post" enctype="multipart/form-data">
    <h2>编辑用户头像</h2>
    <p>用户姓名:<?php echo $info['name'];?></p>
    <p>现有头像:</p><img src="<?php echo './'.$info['id'].'.jpg?rand='.rand() ;?>" onerror="this.src='./default.jpg'" /><br>
    上传头像:<input name="pic" type="file"><br>
    <input type="submit" value="保存头像">
</form>

The running display is as follows:

2, calculate the maximum width and height of the thumbnail

<?php
//设置最大宽度和高度
$maxwidth=$maxheight=90;
//自动计算缩略图的宽和高
if($width>$height){
    //第一种方式
    $newwidth=$maxwidth;
    $newheight=round($newwidth*$height/$width);
}else{
    $newheight=$maxheight;
    $newwidth=round($newheight*$width/$height);
}
  //第二种方式
//    $percent=0.2;   //定义缩略图的缩放比例
//    $newwidth=$width*$percent;
//    $newheight=$height*$percent;

3, based on Make a thumbnail of the original image

<?php
//绘制画布
$thumb=imagecreatetruecolor($newwidth,$newheight);
//依据原图创建一个与原图一样的新的图像
$source=imagecreatefromjpeg($pic_info['tmp_name']);
//依据原图创建缩略图
imagecopyresized($thumb,$source,0,0,0,0,$newwidth,$newheight,$width,$height);

4, and save the thumbnail to the specified directory

<?php
//设置缩略图保存路径
    $new_file='./'.$info['id'].'.jpg';
    //保存缩略图到指定目录
//    header('Content-type:image/jpeg');
    imagejpeg($thumb,$new_file,100);

5, check the running results

The complete code is as follows:

imagesize.php：

<?php
/**
 * Created by PhpStorm.
 * User: Administrator
 * Date: 2018/2/28 0028
 * Time: 下午 1:18
 */
header('Content-type:text/html;charset=utf-8');
$info=array('id'=>1,'name'=>'张三');
//接收并处理上传图像
if(!empty($_FILES['pic'])){
    $pic_info=$_FILES['pic'];
    //获取图片大小
    $image_info=getimagesize($pic_info['tmp_name']);
    echo '<pre>';
    print_r($image_info);
    echo '</pre>';
    $width=$image_info[0];
    $height=$image_info[1];
    //设置最大宽度和高度
    $maxwidth=$maxheight=90;
    //自动计算缩略图的宽和高
    //第一种方式
    if($width>$height){
        $newwidth=$maxwidth;
        $newheight=round($newwidth*$height/$width);
    }else{
        $newheight=$maxheight;
        $newwidth=round($newheight*$width/$height);
    }
    //第二种方式
//    $percent=0.2;   //定义缩略图的缩放比例
//    $newwidth=$width*$percent;
//    $newheight=$height*$percent;
    //绘制画布
    $thumb=imagecreatetruecolor($newwidth,$newheight);
    //依据原图创建一个与原图一样的新的图像
    $source=imagecreatefromjpeg($pic_info['tmp_name']);
    //依据原图创建缩略图
    imagecopyresized($thumb,$source,0,0,0,0,$newwidth,$newheight,$width,$height);
    //设置缩略图保存路径
    $new_file='./'.$info['id'].'.jpg';
    //保存缩略图到指定目录
//    header('Content-type:image/jpeg');
    imagejpeg($thumb,$new_file,100);
}
?>
<form action="" method="post" enctype="multipart/form-data">
    <h2>编辑用户头像</h2>
    <p>用户姓名:<?php echo $info['name'];?></p>
    <p>现有头像:</p><img src="<?php echo './'.$info['id'].'.jpg?rand='.rand() ;?>" onerror="this.src='./default.jpg'" /><br>
    上传头像:<input name="pic" type="file"><br>
    <input type="submit" value="保存头像">
</form>

The running results are as follows: