PHP WebP image metadata processing tutorial

The purpose of this article is to explain how to read and write the metadata of WebP images, including EXIF ​​and XMP data, in PHP. We'll explore the WebP format's support for metadata and provide sample code that demonstrates how to add a metadata block to an existing WebP file. Through this tutorial, you will be able to use PHP to process the metadata of WebP images to better manage and utilize image information.

The WebP format natively supports embedding metadata blocks such as EXIF, XMP and ICCP. This means you can store and read this information in WebP images just like you would a JPEG or PNG image. However, not all PHP image processing libraries natively support reading and writing WebP metadata. Therefore, you may encounter some problems when trying to read or write WebP metadata.

Use exif_read_data() function

PHP's exif_read_data() function is typically used to read the EXIF ​​data of a JPEG or TIFF image. Although WebP images can contain blocks of EXIF ​​data, the exif_read_data() function may not be able to recognize and parse this data directly. This depends on the compilation configuration of PHP and the version of the libexif library used.

If you encounter a "File not supported" warning when using the exif_read_data() function, this may mean that your PHP environment is not configured correctly to support reading EXIF ​​data from WebP images.

Handling WebP metadata manually

If the exif_read_data() function doesn't work, you can try manually reading and writing the metadata block of the WebP file. The WebP format is based on RIFF (Resource Interchange File Format), which uses the concept of chunk to store data. Each chunk contains a 4-byte identifier (FourCC), a 4-byte length value, and the actual payload data.

Here is a sample code that demonstrates how to add an EXIF ​​data block to an existing WebP file:

 <?php /**
 * Add EXIF ​​data to WebP files*
 * @param string $webpFile WebP file path* @param string $exifData EXIF ​​data (binary string)
 *
 * @return bool whether successful*/
function addExifToWebP(string $webpFile, string $exifData): bool
{
    $exifLen = strlen($exifData);
    if ($exifLen % 2 == 1) {
        $exifData .= "\0"; // RIFF requires 16-bit alignment $exifLen;
    }

    $fileHandle = fopen($webpFile, &#39;r &#39;);
    if (!$fileHandle) {
        return false;
    }

    fseek($fileHandle, 0, SEEK_END); // Move to the end of the file fwrite($fileHandle, &#39;EXIF&#39;); // Write the 4-byte chunk ID
    fwrite($fileHandle, pack(&#39;V&#39;, $exifLen)); // Write 4-byte payload length fwrite($fileHandle, $exifData); // Write actual data $fileSize = ftell($fileHandle); // Get new file size fseek($fileHandle, 4, SEEK_SET); // Move to the 5th byte of the file fwrite($fileHandle, pack(&#39;V&#39;, $fileSize - 8)); // Update file size fclose($fileHandle);

    return true;
}

// Example usage $webpFile = &#39;target.webp&#39;;
$exifData = file_get_contents(&#39;source.jpg&#39;); // Read EXIF ​​data from JPEG files (or obtain it in other ways)

// Get EXIF ​​from JPEG
$exif = exif_read_data(&#39;source.jpg&#39;);
// Convert the EXIF ​​array into binary data (requires the use of a third-party library, such as: pel)
// It is assumed here that $exifData already contains binary EXIF ​​data // You can use a third-party library to convert the $exif array into binary data // It is assumed that $exifData already contains binary EXIF ​​data $success = addExifToWebP($webpFile, $exifData);

if ($success) {
    echo "EXIF data successfully added to WebP file!";
} else {
    echo "Failed to add EXIF ​​data!";
}

?>

Code explanation:

1. addExifToWebP function :

   • Receives WebP file path and EXIF ​​data as parameters.
   • Make sure the EXIF ​​data length is even (required by RIFF format).
   • Open the WebP file and move to the end of the file.
   • Writes the EXIF ​​chunk identifier, EXIF ​​data length and actual EXIF ​​data.
   • Update the file size in the WebP file header.
   • Close the file handle.

2. Example usage :

   • Specify the path to the WebP file and the path to the JPEG file containing the EXIF ​​data.
   • Read EXIF ​​data from JPEG files. Note: This is just for demonstration, actual application needs to be adjusted according to your data source. If your EXIF ​​data comes from elsewhere, you need to make sure that the $exifData variable contains the correct binary EXIF ​​data.
   • Call the addExifToWebP function to add EXIF ​​data to the WebP file.
   • Output results.

Things to note:

• Binary EXIF ​​data : The above code assumes that the $exifData variable already contains the correct binary EXIF ​​data. exif_read_data returns an array. You need to use a third-party library (for example: PHP Exiftool or Metadata Extractor Library (PEL)) to convert the PHP array into binary EXIF ​​data.
• Error handling : In actual applications, you should add a more complete error handling mechanism, such as checking whether the file exists, whether the permissions are correct, etc.
• File backup : Before modifying a file, it is best to back up the original file to prevent data loss.
• Other metadata : A similar approach can be used to add other types of metadata blocks such as XMP or ICCP. Simply change the chunk identifier to XMP or ICCP and provide the appropriate metadata content.
• Third-party libraries : It is recommended to use third-party libraries to process EXIF ​​data instead of manually parsing and creating binary data because the EXIF ​​format is more complex.

Summarize

Although PHP's exif_read_data() function may not be able to directly read the EXIF ​​data of WebP images, you can read and write metadata by manually processing the chunks of WebP files. By understanding the structure of the WebP format and the specifications of the RIFF format, you can write PHP code to extract, modify, and add metadata of WebP images to better manage and utilize image information. Remember, using third-party libraries can simplify the process of working with EXIF ​​data.

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