ABCpdf generally regards images as atomic - unbreakable over
more than one page.
However, when an image reaches a certain size, it's impossible
to stop the image from being broken. To try do so would result in
unacceptable gaps in the content. So the assumption that the image
is atomic has to be disregarded.
This property reflects the height (in pixels) at which images
will be redefined as non-atomic.