6 Working with Metadata in Oracle Multimedia Images

6.4.1 EXIF

The Exchangeable Image File Format (EXIF) is the standard for image file storage for digital still cameras. It was developed by the Japan Electronic Industry Development Association (JEIDA) as a standard way of storing images created by digital cameras and metadata about the images. EXIF image metadata can be stored in TIFF and JPEG format images. Oracle Multimedia supports the extraction of EXIF metadata from TIFF and JPEG file formats.

6.4.2 IPTC–IIM

The International Press Telecommunications Council-Information Interchange Model (IPTC-IIM) Version 4 is a standard developed jointly by the International Press Telecommunications Council and the Newspaper Association of America. This metadata standard is designed to capture information that is important to the activities of news gathering, reporting, and publishing. These information records are commonly referred to as IPTC tags.

The use of embedded IPTC tags in image file formats became widespread with the use of the Adobe Photoshop tool for image editing. IPTC metadata can be stored in TIFF and JPEG format images. Oracle Multimedia supports the extraction of IPTC metadata from TIFF and JPEG file formats.

6.4.3 XMP

The Extensible Metadata Platform (XMP) is a standard metadata format, developed by Adobe, for the creation, processing, and interchange of metadata in a variety of applications. XMP uses Resource Description Framework (RDF) technology for data modeling. XMP also defines how the data model is serialized (converted to a byte stream), and embedded within an image file. Oracle Multimedia supports the extraction of XMP metadata from GIF, TIFF, and JPEG file formats. Oracle Multimedia also supports writing XMP data packets into GIF, TIFF, and JPEG file formats.

6.6.1 Creating a Table for Metadata Storage

Before you can extract or embed metadata, you must create the table and columns where the metadata is to be stored. The following PL/SQL code segment creates the photos table with four XMLTYPE columns (metaORDImage, metaEXIF, metaIPTC, and metaXMP) to store each type of image metadata, and two ORDIMAGE columns (image and thumb) for the original image and the thumbnail image, respectively. Each metadata column is bound to its corresponding metadata schema. For example, the metaEXIF column is bound to the XML schema stored at http://xmlns.oracle.com/ord/meta/exif, and is defined as the XML element exifMetadata.

The code statements where the image metadata columns are defined and bound to XML schemas are highlighted in bold.

--
-- Create the PHOTOS table
--
CREATE TABLE photos( id           NUMBER PRIMARY KEY,
                     description  VARCHAR2(40) NOT NULL,
                     metaORDImage XMLTYPE,
                     metaEXIF     XMLTYPE,
                     metaIPTC     XMLTYPE,
                     metaXMP      XMLTYPE,
                     image        ORDSYS.ORDIMAGE,
                     thumb        ORDSYS.ORDIMAGE )
--
-- store full-size images and thumbnail images as SecureFile LOBs
--
LOB(image.source.localdata) STORE AS SECUREFILE
LOB(thumb.source.localdata) STORE AS SECUREFILE
-- and bind the XMLType columns to the Oracle Multimedia metadata schemas
XMLType COLUMN metaORDImage
  XMLSCHEMA "http://xmlns.oracle.com/ord/meta/ordimage"
  ELEMENT "ordImageAttributes"
XMLType COLUMN metaEXIF
  XMLSCHEMA "http://xmlns.oracle.com/ord/meta/exif"
  ELEMENT "exifMetadata"
XMLType COLUMN metaIPTC
  XMLSCHEMA "http://xmlns.oracle.com/ord/meta/iptc"
  ELEMENT "iptcMetadata"
XMLType COLUMN metaXMP
  XMLSCHEMA "http://xmlns.oracle.com/ord/meta/xmp"
  ELEMENT "xmpMetadata";

6.6.2 Extracting Image Metadata

The following PL/SQL procedure extracts metadata from an image and stores it in the specified columns in the photos table you created. This procedure demonstrates the getMetadata( ) method, which returns an array of XML documents. The root element of each document is examined to determine the metadata type. The UPDATE statement stores the documents in the corresponding columns in the photos table.

The code statement where the getMetadata( ) method is called is highlighted in bold.

--
-- fetch the metadata and sort the results
--
PROCEDURE extractMetadata(inID IN INTEGER)
IS
  img ORDSYS.ORDIMAGE;
  metav XMLSequenceType;
  meta_root VARCHAR2(40);
  xmlORD XMLType;
  xmlXMP XMLType;
  xmlEXIF XMLType;
  xmlIPTC XMLType;
 
BEGIN
 
-- select the image
SELECT image
INTO img
FROM PHOTOS
WHERE id = inID;

-- extract all the metadata
metav := img.getMetadata( 'ALL' );
 
-- process the result array to discover what types of metadata were
returned
FOR i IN 1..metav.count() LOOP
  meta_root := metav(i).getRootElement();
  CASE meta_root
    WHEN 'ordImageAttributes' THEN xmlORD := metav(i);
    WHEN 'xmpMetadata' THEN xmlXMP := metav(i);
    WHEN 'iptcMetadata' THEN xmlIPTC := metav(i);
    WHEN 'exifMetadata' THEN xmlEXIF := metav(i);
    ELSE NULL;
  END CASE;
END LOOP;

-- Update metadata columns
--
UPDATE photos
SET metaORDImage = xmlORD,
    metaEXIF = xmlEXIF,
    metaIPTC = xmlIPTC,
    metaXMP = xmlXMP
WHERE id = inID;
 
END extractMetadata;

6.6.3 Embedding Image Metadata

The following PL/SQL procedure demonstrates the putMetadata( ) method. This procedure accepts six arguments. The entry_id argument identifies the image in the photos table to be updated. The remaining arguments (title, creator, date, description, and copyright) are strings to be formatted into an XMP packet and embedded within the target image.

This example creates an XML document instance based on the Oracle Multimedia XML schema for XMP metadata. (This schema is preregistered with Oracle XML DB. See Oracle XML DB Developer's Guide for more information.) The schema for XMP metadata defines a single, global element <xmpMetadata>. The <xmpMetadata> element contains a single, well-formed RDF document. The RDF document contains a single <RDF> element, which is derived from the rdf namespace. This RDF document is constructed using elements defined by the Dublin Core Schema.

The call to the putMetadata( ) method embeds the metadata document into the image file. The UPDATE statement stores the new image and the new metadata back in the photos table.

The code statement where the putMetadata( ) method is called is highlighted in bold.

--
-- write the metadata to the image
--
PROCEDURE write_metadata( entry_id IN VARCHAR2,
                          title IN VARCHAR2,
                          creator IN VARCHAR2,
                          date IN VARCHAR2,
                          description IN VARCHAR2,
                          copyright IN VARCHAR2 )
IS
  img ORDSYS.ORDImage;
  xmp XMLType;
  buf VARCHAR2(5000);
BEGIN
-- select the image
SELECT image
INTO img
FROM PHOTOS
WHERE id = entry_id FOR UPDATE;

-- Create the XMP packet it must be schema valid
-- to "http://xmlns.oracle.com/ord/meta/xmp"
-- and contain an <RDF> element. This example uses
-- the Dublin Core schema.

/* An example XML instance document
 
<xmpMetadata xmlns="http://xmlns.oracle.com/ord/meta/xmp" 
              xsi:schemaLocation="http://xmlns.oracle.com/ord/meta/xmp 
              http://xmlns.oracle.com/ord/meta/xmp" 
              xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
 
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
    <rdf:Description about="" xmlns:dc="http://purl.org/dc/elements/1.1/">
      <dc:title>A Winter Day</dc:title>
      <dc:creator>Frosty S. Man</dc:creator>
      <dc:date>21-Dec-2004</dc:date>
      <dc:description>a sleigh ride</dc:description>
      <dc:copyright>North Pole Inc.</dc:copyright>
    </rdf:Description>
  </rdf:RDF>
</xmpMetadata>
 
*/
 
buf := '<xmpMetadata xmlns="http://xmlns.oracle.com/ord/meta/xmp"
         xsi:schemaLocation="http://xmlns.oracle.com/ord/meta/xmp
         http://xmlns.oracle.com/ord/meta/xmp"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" >
  <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
  <rdf:Description about="" xmlns:dc="http://purl.org/dc/elements/1.1/">';
 
IF title IS NOT NULL THEN
  buf := buf || '<dc:title>' || htf.escape_sc(title) || '</dc:title>';
END IF;
 
IF creator IS NOT NULL THEN
  buf := buf || '<dc:creator>' || htf.escape_sc(creator)
             || '</dc:creator>';
END IF;
IF date IS NOT NULL THEN
  buf := buf || '<dc:date>' || htf.escape_sc(date)
             || '</dc:date>';
END IF;
IF description IS NOT NULL THEN
  buf := buf || '<dc:description>' || htf.escape_sc(description)
             || '</dc:description>';
END IF;
IF copyright IS NOT NULL THEN
  buf := buf || '<dc:copyright>' || htf.escape_sc(copyright)
             || '</dc:copyright>';
END IF;
 
buf := buf || '
  </rdf:Description>
  </rdf:RDF>
  </xmpMetadata>';

-- create the XML document
xmp := XMLType.createXML(buf, 'http://xmlns.oracle.com/ord/meta/xmp');
 
-- write the metadata
img.putMetadata( xmp, 'XMP' );
 
-- update the image
UPDATE photos
SET image = img,
    metaXMP = xmp
WHERE id = entry_id;
 
END write_Metadata;