PDFlib Text Extraction Toolkit (TET) Manual

Document-oriented image extraction: the application is interested in all images in
the document, but doesn’t care which image is used on which page. Images which
are placed more than once should be extracted only once.
In order to extract an image, the corresponding image ID is required. The image ID is
used as an index in the pCOS images[ ] array, and can be obtained in the following ways
which correspond to page-oriented and document-oriented image extraction, respectively:
> TET_get_image_info( ) retrieves geometric information about a placed image as well
as the pCOS image ID (in the imageid field of TET_image_info) of the underlying image
data. This ID can be used to retrieve more image details with TET_pcos_get_number( ),
such as the color space, width and height in pixels, etc., as well as the actual pixel
data with TET_write_image_file( ) or TET_get_image_data( ). TET_get_image_info( ) will
not touch the actual pixel data of the image. If the same image is referenced multiply
on one or more pages, the corresponding IDs will be the same.
This method for page-oriented image extraction is demonstrated in the extractor
mini sample and the image_extractor topic in the TET Cookbook.
> Enumerate all values from 0 to the highest image ID, which is queried with TET_pcos_
get_number( ) as the value of the pCOS path length:images. Note that the relationship
of images and pages will be lost in this case.
Once an image ID has been retrieved, the functions TET_write_image_file( ) or TET_get_
image_data( ) can be called to write the image data to a disk file or fetch the pixel data in
memory, respectively.
XMP metadata for images. PDF uses the XMP format to attach metadata to the whole
document or parts of it. You can find more information about XMP and its use in PDF at
the following location: www.pdflib.com/developer/xmp-metadata.
An image object may have XMP metadata associated with it in the PDF document. If
XMP metadata is present, TET will by default embed it in the extracted image for the
output formats JPEG and TIFF. This behavior can be controlled with the keepxmp option
of TET_write_image_file( ) and TET_get_image_data( ). If this option has been set to false,
TET will ignore image metadata when generating the image output file.
The image_metadata topic in the pCOS Cookbook shows how to extract image metadata
with the pCOS interface directly, without generating any image file.
82 Chapter 7: Image Extraction