How to extract focus information of a photo using PHP and Exif extension

How to use PHP and Exif extensions to extract focal length information from photos

Introduction:
With the popularity of digital photography, the number of photos people take is also growing. For photography enthusiasts, it is very important to understand the metadata information of photos. This article will introduce how to use PHP and Exif extensions to extract the focal length information of photos to help readers better understand their photos.

1. What is Exif data?
Exchangeable Image File Format (Exchangeable Image File Format), referred to as Exif, is a file format for recording digital photo information. It uses some storage units to record the shooting parameters and shooting environment information of the photo, such as focal length, ISO, shutter speed, etc. The Exif extension of PHP provides a set of functions to easily process and extract Exif data.

2. Install and configure the Exif extension
Before using the Exif extension, we need to confirm whether PHP has installed the extension. You can check it with the following command:

php -m | grep exif

If you can see 'exif', it means that the Exif extension has been installed. If it is not installed, you can install it through the following steps:

1. Run the following command in the terminal to install the Exif extension:

   sudo apt-get install php-exif

2. Edit the php.ini file :

   sudo nano /etc/php/7.4/cli/php.ini

3. Find the following line and uncomment it:

   ;extension=exif

4. Save and exit the file.

5. Restart PHP:

   sudo service php7.4-fpm restart

3. Extract the focal length information of the photo
Next, we will extract the focal length information of the photo through the following steps:

1. Create a PHP script named exif_example.php and place the photos in the same directory as the script.

2. In the script, first read the Exif data of the photo through the function exif_read_data() and save it in an array:

   <?php
   $filename = 'example.jpg'; // 照片文件名
   $exif_data = exif_read_data($filename, 0, true);
   ?>

3. Then, Determine whether the focal length information exists and print it out:

   <?php
   if (isset($exif_data['EXIF']['FocalLength'])) {
    $focal_length = $exif_data['EXIF']['FocalLength'];
    echo "照片的焦距为：{$focal_length}mm";
   } else {
    echo "未能获取照片的焦距信息。";
   }
   ?>

4. Run and test
Save the script and run the following command in the terminal:

php exif_example.php

If focal length information exists in the photo, you will see output similar to the following:

照片的焦距为：50mm

Otherwise, if there is no focal length information in the photo, you will see the following output:

未能获取照片的焦距信息。

5. Summary
By using PHP's Exif extension, we can easily extract the focal length information of the photo. However, it should be noted that not all photos contain focal length information. Therefore, when processing photos, we should be prepared for this and handle exceptions. I hope this article helps you understand how to use PHP and Exif extensions to extract focus information from photos. Happy shooting!

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