PDF/Raster was a project started by the TWAIN Working Group in 2014 as part of its TWAIN Direct project to connect scanners to applications through networks. The TWAIN Working Group has worked in conjunction with the PDF Association in the development of the PDF/raster specification, to make sure PDF/raster is a proper subset of PDF in order to move forward with the formal ISO process.
PDF/raster is intended to be a standard format for storing, transporting and exchanging scanned documents. As a subset of PDF, it takes advantage of the widespread support for viewing, printing and processing PDF files. As a narrowly restricted subset of PDF, it is much simpler to generate and interpret, allowing it to replace the TIFF and JPEG file formats for capture and delivery of scanner output.
In considering which file formats to allow in the specification a variety of considerations were important:
• Support was desired for uncompressed data, for simplicity and compatibility with the original TWAIN specification.
• Support for JPEG files was deemed important for high-speed color scanning operations.
• Support for bitonal Group 4 compressed data was essential, since it is still very common in mainstream business scanning.
• JPEG 2000 support and JBIG2 support seemed like desirable future extensions for a later revision of the standard.
• Extensible and easily-standardized image metadata was deemed an essential feature.
It was important that the file format used as a basis to:
• Fit well into existing workflows and toolchains
• Be subsettable so either existing (large) libraries or a newly-developed small library could be used (important for an embedded system like scanner firmware)
In a networked scanning architecture, protection features for data being transmitted remotely become more important than in a local scanning scenario, so the following were deemed important:
• Authentication (to ensure data has not been tampered with in transit)
• Resistance to malware (exclusion of executable code and fonts)