PDFlib Text Extraction Toolkit (TET) Manual

When are images merged? Analyzing and merging images on a page are triggered by
the corresponding call to TET_open_page( ). This leads to the following important consequences:
> The number of entries in the pCOS images[ ] array, i.e. the value of the length:images
pseudo object, may increase: as more pages are processed, artificial images which result
from image merging are added to the array. In order to extract all merged images
you must therefore open all pages in the document before querying length:images
and extracting image data. Artificial (merged) images are marked with the corresponding
flag artificial (numerical value 1) in the images[ ]/mergetype pseudo object.
> On the other hand, elements in the images[ ] array may only be used as parts of
merged images. However, entries are never removed from the images[ ] array, but the
consumed entries are marked with the corresponding flag consumed (numerical value
2) in the images[ ]/mergetype pseudo object.
How many images are in a document? Surprisingly, there is no simple answer to this
simple question. The answer depends on the following decisions:
> Do you want to count image resources or placed images?
> Do you want to take images into account which are only used as parts of merged images,
but are never placed isolated?
Using TET and pCOS pseudo objects you can determine all variants of the image count
answer. The image_count topic in the TET Cookbook demonstrates various possibilities
of image counting. It generates output like the following:
No of raw image resources before merging: 82
No of placed images: 12
No of images after merging (all types): 83
normal images: 1
artificial (merged) images: 1
consumed images: 81
No of relevant (normal or artificial) image resources: 2
Small image filtering. TET ignores very small images if may of those is present on the
page. Since the image merging process often combines many small images to a larger
image, small image removal is performed after image merging. Only images which can
not be merged to form a larger image will be candidates for small image removal. In addition,
they must satisfy the conditions for size and count which can be specified in the
maxarea and maxcount suboptions of the smallimages suboption of the imageanalysis
page option. In order to completely disable small image removal use the following page
option:
imageanalysis={smallimages={disable}}
116 Chapter 8: Image Extraction