CHAPTER 7
7
Transparency
PDF 1.4 extends the Adobe imaging model to include the notion of
transparency.
Transparent objects do not necessarily obey a strict opaque painting model but
can blend
(composite)
in interesting ways with other overlapping objects. This
chapter describes the general transparency model but does not cover how it is im-
plemented. Implementation-like descriptions are used at various points to de-
scribe how things work, for the purpose of elucidating the behavior of the model.
The actual implementation will almost certainly be different from what these de-
scriptions might imply.
The chapter is organized as follows:
•
transparency model and its associated terminology.
•
involved in compositing a single object with its backdrop.
•
transparency
groups
and describes their properties and behavior.
•
position-dependent shape and opacity.
•
properties are represented in a PDF document.
•
actions between transparency and other aspects of color specification and
rendering.
513