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Writing IPTC IIM/headers

The most difficult part with IPTC is writing the headers. While iptcparse() unpacks the binary data, iptcembed() doesn’t automatically pack it. Fortunately the author of the iptc* functions (Thies C. Arntzen) made a user function to pack this. (Although I wonder why it wasn’t put into iptcembed()):

// Function to format the new IPTC text
// (thanks to Thies C. Arntzen)
function iptc_maketag($rec,$dat,$val){
    $len = strlen($val);
    if ($len < 0x8000)
        return chr(0x1c).chr($rec).chr($dat).
        chr($len >> 8).
        chr($len & 0xff).
        $val;
    else
        return chr(0x1c).chr($rec).chr($dat).
        chr(0x80).chr(0x04).
        chr(($len >> 24) & 0xff).
        chr(($len >> 16) & 0xff).
        chr(($len >> 8 ) & 0xff).
        chr(($len ) & 0xff).
        $val;
}

Not exactly well documented, but the parameters are like this:

$rec: Application record. (We’re working with #2)
$dat: Index. (120 for caption, 115 for contact. See the IPTC IIM specification)
$val: Value/data/text. Make sure this is within the length constraints of the IPTC IIM specification

This will return an IPTC binary block that we can embed into an image with iptcembed(). iptcembed() will return a full image binary string with the iptc block, and we will have to write that to a file.

$caption_block = iptc_maketag(2, 120, 'This is my caption');
$image_string = iptcembed($caption_block,
                'untouched_old_image.jpg');
file_put_contents('new_file_with_iptc.jpg', $image_string);

Now new_file_with_iptc.jpg is the same image as untouched_old_image.jpg, just with the iptc block written.

There you go. I’m impressed if you read all three pages, but now you’re set to work with images with Exif and IPTC embedded. Hope you enjoyed it.

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