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The process of converting the codes contained in a portable document format (PDF) file into a two-dimensional (2D) image is known as PDF rasterization. The information stored in a PDF file can give a program or device instructions on how to display the document but, when being viewed on a screen, the results must be drawn in a 2D space. Depending on the type of objects used in a PDF document, the process of PDF rasterization can sometimes be accelerated through the use of graphics hardware, much in the same way that three-dimensional (3D) graphics are calculated. There are a number of complex issues associated with PDF rasterization, especially if a document includes dynamic interactive elements or programming scripts that rely on external objects that are not easily converted into a static 2D image.
A PDF document is stored as a series of instructions and numbers that can tell a program how to draw not only the text on a page, but also any graphics that are required, whether they are compressed images or vector-based line art. PDF files store information in this way so it can be completely independent of the device being used to render, display or print it without any loss of quality. Even though there are devices — such as PostScript® printers or vector-based displays — that can display a PDF document natively, most practical systems need to convert the stored instructions into a 2D image so they can be used by hardware such as monitors and home printers.
PDF rasterization involves using mathematical formulas and some other techniques to translate objects such as Bezier curves, lines and fonts onto a flat area, pixel by pixel. The PDF file saves how to draw the information, so a rasterization image processor (RIP) can make the PDF document as large or small as desired without any loss of quality. One instance in which this might not be true involves photographic-style image files that are embedded or encoded into a PDF document and the number of pixels is already set and cannot be scaled without interpolation that could degrade the quality.
Many computers perform PDF rasterization on a daily basis. A PDF reader, such as those used in web browsers, can quickly render PDF files so they can be read, although the speed of display is sometimes made possible by a reduction in quality as the program takes rendering shortcuts. Whenever a PDF document is printed, it also must be rasterized before being sent to the hardware. Mobile devices often have PDF rasterization functionality built directly into their operating systems to allow for accurate hardware accelerated rendering, no matter what the size of the output field.