Introduction to VDP and VDP Transparency

VDP stands for Variable Data Printing. This term is closely related to Personalized Publishing. The main idea is to produce personalized documents relevant to the recipients. To increase the appeal of the personalized documents, they typically contain rich graphics and images. To make this economical, the personalized documents must be printed at engine speeds of hundreds and even thousands of  pages per minute). This speed cannot be achieved using static languages such as PostScript and PDF. Thus VDP languages are used. The speed is achieved by marking what is reusable and what is not reusable.

A typical optimized VDP consumer (known as Print Controller, or DFE) performs the following operations:

1. Render reusable elements and caching the raster
2. Render non-reusable elements
3. Merge reusable and non-reusable elements together producing the final pages.

In order to achieve the engine speed:

1. Merging of the elements to the final pages must run at the engine speed.
2. Rendering non-reusable elements must run at least at the engine speed.
3. Rendering and caching reusable elements must run at reasonable speed.

All the existing VDP languages, such as IBM IPDS, Creo/Kodak VPS, Xerox VIPP, HP JLayout, and PODi PPML use the opaque merging model. That is, when 2 pixels are merged together:

•  If the top pixel is marked, the top pixel replaces the bottom pixel;
•  If the top pixel is unmarked (i.e. blank or empty), the top pixel is ignored and the bottom pixel stays intact.

PPML-3 and PDF/VT change this simple merging model. Now when the elements are merged together the following needs to be taken into account:

• Opacity. Each element at each point contains opacity value (known also as alpha-mask).
• Blend Mode. PDF Transparency Model defines 16 blending modes.
• Blending Color Space. The result of blending depends on whether the blending calculations are performed in RGB or CMYK space.

And if PDF/VT complexity is not carefully contained, possibly other transparency attributes as well as the internal element structure must be taken into account.

The printing industry faces a serious challenge. The transparency blending bitmap on the screen is produced by applications (such as Adobe InDesign and others).  The blending bitmpap on the printed page is produced by Print Technologies (such as Creo Spire, EFI Fiery, or vdptech rendering/merging technology). How do we make sure that the result on the screen matches the result on the page? The only viable solution is keeping PDF/VT Transparency Model simple and unambiguous. Otherwise, VDP Transparency Revolution arrives just on time to be greeted by TypeWriters, TapeRecorders, Dinosaurs, and other indispensable creatures in the paradise of non-existence.

The examples on this website can be used for basic verification to be used by PDF/VT producers and PDF/VT consumers.