How to use PHP to optimize the image file size and quality of your website

In today's visual-oriented era, the image quality of the website is very important. However, high-resolution image files often cause the website to load slower, reduce user experience, and affect website rankings. Therefore, in the development of the website, we need to use PHP to optimize the size and quality of images and improve the speed and user experience of the website. Here are several ways to optimize image size and quality using PHP.

1. Use PHP's GD library

PHP's GD library is an extension for image processing. It can help us perform a series of operations such as scaling, cropping, rotating, and adding watermarks to images. Using this library to optimize images can achieve lossless compression, that is, reducing the size of the image without affecting the quality of the image. The following is an example of image compression through the GD library:

// 获取原始图片
$image = imagecreatefromjpeg('original_image.jpg');
// 获取原始图片的宽度和高度
$width = imagesx($image);
$height = imagesy($image);
// 计算缩小的比例
$scale = 0.5;
// 计算新的宽度和高度
$new_width = $width * $scale;
$new_height = $height * $scale;
// 创建新的图片
$new_image = imagecreatetruecolor($new_width, $new_height);
// 进行缩放
imagecopyresampled($new_image, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
// 输出新的图片
imagejpeg($new_image, 'new_image.jpg', 80); // 80代表图片质量，可自行调整
// 释放内存
imagedestroy($image);
imagedestroy($new_image);

In this example, we use the GD library to compress an original image and output a new image. Among them, the imagecopyresampled() function can achieve image scaling and cropping while maintaining the quality of the image.

2. Use third-party tools for image compression

In addition to the GD library, there are also some third-party tools that can help us optimize images. For example, we can use online tools such as TinyPNG or Kraken to compress images. These tools can interact with the API through PHP's cURL extension to achieve lossless compression of images. The following is an example of using TinyPNG for image compression:

// 引入curl库
require('vendor/autoload.php');
// 获取图片内容
$image_content = file_get_contents('original_image.jpg');
// 初始化curl
$curl = curl_init();
// 设置curl的参数
curl_setopt_array($curl, array(
  CURLOPT_URL => 'https://api.tinify.com/shrink',
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_HTTPHEADER => array(
    'Authorization: Basic ' . base64_encode('api_key:'),
    'Content-Type: application/json'
  ),
  CURLOPT_POSTFIELDS => json_encode(array(
    'source' => base64_encode($image_content),
  ))
));
// 执行curl并获取压缩后的图片内容
$response = curl_exec($curl);
// 获取压缩后的图片的大小
$new_size = curl_getinfo($curl, CURLINFO_SIZE_DOWNLOAD);
// 关闭curl
curl_close($curl);
// 解析返回的JSON数据
$data = json_decode($response, true);
// 获取压缩后的图片
$new_image_content = file_get_contents($data['output']['url']);
// 输出压缩后的图片
file_put_contents('new_image.jpg', $new_image_content);

In this example, we use TinyPNG's API to compress images, obtain the compressed image content, and output the compressed images.

3. Use responsive images

Responsive images refer to images that can automatically adjust the image size and quality according to different screen sizes, pixel density and other conditions. Using responsive images can reduce the load time and bandwidth usage of your web pages while improving the user experience. We can use PHP to generate responsive images. The following is an example of using PHP to generate responsive images:

// 获取原始图片
$image = imagecreatefromjpeg('original_image.jpg');
// 获取原始图片的宽度和高度
$width = imagesx($image);
$height = imagesy($image);
// 定义响应式图片尺寸
// 可自行根据项目需求设置
$sizes = array(
  '(max-width: 640px) 100vw',
  '50vw',
  '33.3vw'
);
// 定义缩放比例
$scales = array(
  1,
  0.5,
  0.3
);
// 输出响应式图片
echo '<img srcset="';
foreach ($sizes as $key => $size) {
  $new_width = $width * $scales[$key];
  $new_height = $height * $scales[$key];
  $new_image = imagecreatetruecolor($new_width, $new_height);
  imagecopyresampled($new_image, $image, 0, 0, 0, 0, $new_width, $new_height, $width, $height);
  imagejpeg($new_image, 'new_image_'.$key.'.jpg', 80); // 80代表图片质量，可自行调整
  echo 'new_image_'.$key.'.jpg ' . $size . ($key == count($sizes)) ? '' : ',';
  imagedestroy($new_image);
}
echo '" sizes="(max-width: 640px) 100vw, (max-width: 1024px) 50vw, 33.3vw" />';
// 释放内存
imagedestroy($image);

In this example, we first adjusted the size and quality of the original image through the GD library, and then generated responsive images according to different sizes and scaling ratios. image. Finally, we output the responsive image through the <img> tag in HTML.

In summary, it is very important to use PHP to optimize the image file size and quality of the website, which can effectively improve the speed and user experience of the website. We can optimize through methods such as GD library, third-party compression tools, and responsive images. At the same time, choosing an appropriate optimization strategy based on the actual needs of the project and user experience is the key.

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