I'm trying to run a little function to determine the luminance of an image and store that in the postmeta for that image..

I have the function working, but id like it to fire when an image has finished uploading.. does anyone know the function/filter/action i should hook into for this?

ive looked at

• image_attachment_fields_to_save
• attachment_fields_to_save
• wp_handle_upload
• media_upload_form_handler
• wp_generate_attachment_metadata

and i just cant seem to make any of them simply run an addition to the postmeta table for the image

currently my code looks something like:

function insert_luminance_data($post, $attachment) {
    if ( substr($post['post_mime_type'], 0, 5) == 'image' ) {
        $lum = 'TEST';
        add_post_meta( $post['ID'], 'image_lum', $lum, true ) || update_post_meta( $post['ID'], 'image_lum', $lum );
    }
    return $post;
}

add_filter('image_attachment_fields_to_save', 'insert_luminance_data', 10, 2);

but this isnt working.

Thanks in advance for any assistance