PHP image processing functions: image processing technology of imagecreatefromjpeg, imagecopyresized, imagepng and other functions

Introduction to PHP image processing functions: image processing technology of imagecreatefromjpeg, imagecopyresized, imagepng and other functions

Image processing plays an important role in modern network applications, regardless of Whether it is uploading user avatars, generating thumbnails, or graphics processing in applications, they are all inseparable from the support of image processing functions. Among them, PHP provides a series of powerful image processing functions. This article will focus on the usage skills of imagecreatefromjpeg, imagecopyresized, imagepng and other functions, and give specific code examples.

1. imagecreatefromjpeg function

The function of imagecreatefromjpeg function is to create an image resource from a JPEG format picture. Its use is very simple, just pass the image path as a parameter to the function. The following is a simple example:

$source_image = imagecreatefromjpeg('source.jpg');

In this way, the $source_image variable becomes an image resource containing JPEG images, which we can subsequently process through other image processing functions.

2. imagecopyresized function

The imagecopyresized function is a function used to scale images. It scales an image resource to a specified size and saves the new image into another image resource. The function is used as follows:

$destination_image = imagecreatetruecolor($new_width, $new_height);
imagecopyresized($destination_image, $source_image, 0, 0, 0, 0, $new_width, $new_height, $original_width, $original_height);

In the above code, $new_width and $new_height are the scaled image sizes we expect, and $original_width and $original_height are the sizes of the original images. A new image resource $destination_image is created through the imagecreatetruecolor function, and then the $source_image is scaled and copied to $destination_image using the imagecopyresized function.

3. imagepng function

The imagepng function is a function that saves image resources in PNG format. Through this function, we can save the image processing results in PHP as a PNG format file. The usage method is as follows:

imagepng($destination_image, 'output.png');

The above code saves the $destination_image image resource as an output.png file.

Comprehensive application example:

Now, let’s look at an example of a comprehensive application. By combining the above three functions, a simple image processing function is implemented to process the uploaded user avatar image. Scale and save as thumbnail in PNG format. Assume that there is a file input box named avatar in the front-end file upload form.

if ($_FILES['avatar']['error'] === UPLOAD_ERR_OK) {
  $source_image = imagecreatefromjpeg($_FILES['avatar']['tmp_name']);
  $original_width = imagesx($source_image);
  $original_height = imagesy($source_image);

  $new_width = 100;
  $new_height = 100;

  $destination_image = imagecreatetruecolor($new_width, $new_height);
  imagecopyresized($destination_image, $source_image, 0, 0, 0, 0, $new_width, $new_height, $original_width, $original_height);

  $output_file = 'thumbnails/' . time() . '.png';
  imagepng($destination_image, $output_file);

  imagedestroy($source_image);
  imagedestroy($destination_image);

  echo '缩略图保存成功：' . $output_file;
} else {
  echo '上传失败';
}

Through the above code, we can scale the avatar uploaded by the user to the size of 100x100 and save it as a thumbnail in PNG format. Thumbnails are named with timestamps and stored in the thumbnails directory. At the same time, after the image is processed, the image resource is destroyed through the imagedestroy function and the server memory is released.

By using PHP's image processing functions, we can easily implement various image processing needs, such as generating thumbnails, adding watermarks, etc. These efficient and easy-to-use functions provide web developers with powerful image processing capabilities and provide strong support for creating rich user experiences. Hope this article helps you!

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