如何使用GD调整上传图像并将其转换为PNG？

sudo apt-get install php-gd

<form action="upload.php" method="post" enctype="multipart/form-data">
   <input type="file" name="image" />
   <input type="submit" value="Upload" />
</form>

<?php
$image = $_FILES['image']['tmp_name'];
$filename = $_FILES['image']['name'];
$image_info = getimagesize($image);
$width = $image_info[0];
$height = $image_info[1];

// 创建一个新的图像资源
$new_image = imagecreatetruecolor($width, $height);

// 根据文件类型选择合适的图像创建函数
switch ($image_info['mime']) {
    case 'image/jpeg':
        $image_create_func = 'imagecreatefromjpeg';
        break;
    case 'image/png':
        $image_create_func = 'imagecreatefrompng';
        break;
    case 'image/gif':
        $image_create_func = 'imagecreatefromgif';
        break;
    default:
        throw new Exception('Unknown image type');
}

// 从上传的图像文件创建一个图像资源
$src_image = $image_create_func($image);

// 将源图像复制到新图像资源中，并调整大小
imagecopyresampled($new_image, $src_image, 0, 0, 0, 0, $width, $height, $width, $height);

// 将新图像资源保存为PNG文件
imagepng($new_image, 'uploads/' . $filename . '.png');

// 释放内存
imagedestroy($new_image);
imagedestroy($src_image);

echo 'Image uploaded and converted to PNG';
?>