利用PHP和GD库实现图片缩放并保持比例的方法

<?php
// 原始图片路径
$source_image = 'path/to/source/image.jpg';
// 目标图片路径
$target_image = 'path/to/target/image.jpg';
// 目标图片宽度
$target_width = 300;
// 目标图片高度
$target_height = 200;

// 获取原始图片的宽度和高度
list($source_width, $source_height) = getimagesize($source_image);

// 计算缩放比例
$scale = min($target_width/$source_width, $target_height/$source_height);

// 计算缩放后的宽度和高度
$new_width = $source_width * $scale;
$new_height = $source_height * $scale;

// 创建一张新的图片
$new_image = imagecreatetruecolor($new_width, $new_height);

// 根据原始图片的扩展名创建相应的图片对象
$extension = pathinfo($source_image, PATHINFO_EXTENSION);
if ($extension == 'jpg' || $extension == 'jpeg') {
    $source = imagecreatefromjpeg($source_image);
} elseif ($extension == 'png') {
    $source = imagecreatefrompng($source_image);
} elseif ($extension == 'gif') {
    $source = imagecreatefromgif($source_image);
}

// 将原始图片缩放到新的尺寸
imagecopyresampled($new_image, $source, 0, 0, 0, 0, $new_width, $new_height, $source_width, $source_height);

// 保存缩放后的图片到目标路径
imagejpeg($new_image, $target_image, 100);

// 释放资源
imagedestroy($source);
imagedestroy($new_image);

echo "Image scaled and saved successfully!";
?>