Overview of imposition in pdfToolbox

pdfToolbox contains a somewhat unusual but quite complete imposition engine. It has significantly grown over the years, and is used in the product in a few different ways. All that together makes this chapter about imposition a long one. This article explains some of the basic principles and history behind the imposition engine, provides some insight into capabilities and limitations, and introduces the three big ways the imposition engine can be used today. The rest of the chapter fills in the details on all of this.

The callas YouTube channel contains quite some information about imposition as well; the different articles in this chapter are linked appropriately with individual videos.

Architecture of the engine

Where many imposition applications use visual template editors, and are optimized to handle imposition tasks manually, this has never been the goal of the pdfToolbox imposition engine. pdfToolbox focuses (as in most other places) on automation. As a result, the functionality is oriented much more toward reaching the highest possible throughput, rather than a comfortable user interface.

Because of this, the engine has a quite steep learning curve sometimes. But at the same time, it is ideally suited for tasks that are perhaps not 'classic' imposition. The imposition engine is used in many different projects where other imposition applications wouldn't be suitable. And because the imposition functionality can be combined with all of the other functionality in pdfToolbox (for example in process plans), it can be incredibly versatile.

Capabilities and limitations

In its most elementary form, the imposition engine takes a single input file, and produces a single output file. Because pdfToolbox also provides the capabilities to split and merge PDF files,  pull in additional PDF files where needed, and do advanced calculations using JavaScript, the engine still covers a lot of ground.

The engine does have a number of limitations:

  • There is no visual template editor. While there are a few simple imposition capabilities, the majority of the imposition functionality requires you to write imposition configurations. This makes the imposition engine impractical for situations where there is a high variability of input jobs (one-offs).
  • There is no built-in support for ganging multiple files together (Ganging as in, combining multiple PDF files or PDF file pages on a single imposed sheet while maximizing sheet coverage. As JavaScript is supported, certain scenarios can be handled quite well, but the engine has no optimization capabilities.
  • Imposition is always based on rectangular pages. There is no built-in support for nesting pages together based on a cut contour shape. Again, if you know what jobs need to be imposed and what their geometry is, the imposition engine can be used to impose them, but it cannot calculate optimal coverage by itself.

Different imposition modes

This chapter explores three big ways the imposition engine can be used. Summarized, they are:

  1. Simple Imposition
    These are imposition features for which no imposition configurations need to be made. Examples are "Step and repeat", "Fill page", "Booklet imposition"... These are typically available in the Switchboard, and as Actions, both for use in process plans, and through the CLI or SDK. All help articles regarding this functionality start with "Simple imposition".
  2. JavaScript imposition
    The modern way to create imposition configurations in pdfToolbox is using JavaScript. All articles beginning with "JavaScript imposition" speak specifically about this type of imposition configuration. The imposition configurations created this way can be used in the Switchboard, but also using an "Impose" action, both in process plans, and through the CLI or SDK.
  3. Old-style imposition
    Before JavaScript imposition configurations existed, pdfToolbox featured its own tabbed-text imposition configuration language. While this is quite powerful, it can also be a bit of a pain to get correct. Because of this, and because the JavaScript imposition now supports more features than the old-style language, it is advised to use JavaScript imposition instead. The help articles for the old-style imposition are still available in this chapter: they all start with "Old-style imposition".

Besides these three imposition modes, this chapter contains a number of more generic articles. You're reading one now, but there are also articles on terminology, editing and debugging configurations, and so on. They are typically useful for more than one imposition mode.