Using PHP to Extract Image Exif Data
Posted by Nessa | Posted in uncategorized | Posted on 02-08-2010
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Those of us fluent in digital photography have come across the term “Exif data” numerous times when it comes to software we use to digitally manipulate photographs. Exif (Exchangeable image file format) data is generally used to identify the properties of the camera that snapped a picture, and usually the software that altered it afterwards. It can tell you when a picture was taken, what kind of camera took it, as well as the camera’s model, shutter speed, focal length, and even provide a thumbnail of the image on the camera’s LCD screen.
Why would you need to extract this information? If you’re ever uploaded images to stock photography sites and wonder how they know so much about your pictures, it’s because they extract the Exif data from your pictures to provide more information on how they were taken. This quick tutorial will demonstrate how to extract Exif data from an image using PHP.
Enabling the Exif Extension
The Exif functions for PHP may not be native to your installation, so you can check by viewing your phpinfo file or running “php -m” via command line to see a list of modules compiled in. If you don’t see Exif listed, there are three ways you can enable it depending on how you installed PHP:
- If you compiled PHP manually, you can re-compile while adding –enable-exif to the configure line
- If PHP is installed via package (rpm/deb), it should already have Exif enabled. If not, you can install an RPM for the extension manually
- If you use cPanel, run EasyApache and select the Exif extension from the PHP module list, and recompile
Determining the Image Type
The exif_imagetype function identifies the format of an image, but returns the result as a code. The PHP function reference provides a full list of these return codes, but 1-8 are the most common out of the 16:
1: GIF
2: JPEG
3: PNG
4: SWF
5: PSD
6: BMP
7/8: TIFF
Here’s a code example that lists all the desired valid image types in an array and detects the type of image from the specified file, returning the result in “human readable” format:
<?php
$image = "/path/to/myimage";
$types = array(
1 => "GIF",
2 => "JPEG",
3 => "PNG",
4 => "SWF",
5 => "PSD",
6 => "BMP",
7 => "TIFF",
8 => "TIFF"
);
$imagetype = exif_imagetype($image);
if (array_key_exists($imagetype, $types)) {
echo "Image type is: " . $types[$imagetype];
} else {
echo "Not a valid image type";
}
?>
Reading Exif Header Data
The exif_read_data function can be used to extract header data from JPEG and TIFF files:
<?php
$image = "/path/to/myimage";
$exif = exif_read_data($image, 0, true);
foreach ($exif as $key => $section) {
foreach ($section as $name => $val) {
echo "$key.$name: $val\n";
}
}
?>
This will return the elements of the array from exif_read_data, which can be very long depending on what information is available for the image. There are seven sections (arrays) of data types:
- FILE: Contains the file’s name, size, timestamp, and what other sections were found (as listed below)
- COMPUTED: Contains the actual attributes of the image
- ANY_TAG: Any information that is tagged
- IFD0: Mostly contains information about the camera itself, the software used to edit the image, when it was last modified, etc
- THUMBNAIL: Information about the embedded thumbnail for the image
- COMMENT: Comment headers for JPEG images
- EXIF: Contains more information supplementary to what is in IFD0, mostly related to the camera (includes focal length, zoom ratio, etc)
Depending on the information available for the image, you’ll actually see a lot of data in the output. Say, for instance, you want to only output the IFD0 data to see the information of the camera that took the image:
<?php
$image = "image.jpg";
$exif = exif_read_data($image, 0, true);
foreach ($exif as $key => $section) {
foreach ($section as $name => $val) {
if($key == "IFD0"){
echo "$key.$name: $val\n";
}
}
}
?>
This will output:
IFD0.ImageWidth: 2592 IFD0.ImageLength: 3872 IFD0.BitsPerSample: Array IFD0.Compression: 1 IFD0.PhotometricInterpretation: 2 IFD0.Make: NIKON CORPORATION IFD0.Model: NIKON D80 IFD0.Orientation: 1 IFD0.UndefinedTag:0x0000: IFD0.XResolution: 72/10000 IFD0.YResolution: 72/1 IFD0.PlanarConfiguration: 1 IFD0.ResolutionUnit: 2 IFD0.Software: Adobe Photoshop CS4 Windows IFD0.DateTime: 2010:02:06 22:24:09 IFD0.Exif_IFD_Pointer: 304
Or, you can further narrow down the output by specifying specific values in the $exif multi-dimensional array:
<?php
$image = "image.jpg";
$exif = exif_read_data($image, 0, true);
echo "Software: " . $exif['IFD0']['Software'] . "\n";
?>
This will return:
Software: Adobe Photoshop CS4 Windows
Using Exif to generate a thumbnail
As touched on previously, many cameras and image manipulation software will include an embedded thumbnail for an image. You can extract this thumbnail using the exif_thumbnail function:
<?php
$image = "image.jpg";
$thumbnail = exif_thumbnail($image, $width, $height, $type);
echo "<img width='$width' height='$height' src='data:image;base64,".base64_encode($thumbnail)."'>";
?>
Keep in mind that the thumbnail generated here is from the Exif data – there are other ways to create a thumbnails using many of the PHP image functions.
