Raster Image Processor (RIP)

History

The RIP concept is inseparable from the rise of the page-description language (PDL). Its lineage runs through Xerox PARC, where the Interpress page-description language was developed and where John Warnock was among the group that worked on it. Warnock and Charles Geschke founded Adobe Systems in 1982 and developed PostScript, released in 1984 as a device-independent PDL. PostScript was created at Adobe by John Warnock, Charles Geschke, Doug Brotz, Ed Taft, and Bill Paxton over 1982 to 1984.

The commercial turning point was the Apple LaserWriter, announced on January 23, 1985, the first printer to ship with a PostScript interpreter, an event widely credited with sparking the desktop publishing revolution. Because a PostScript interpreter's job is to turn PostScript into printer dots, such interpreters came to be called PostScript raster image processors, and through the 1980s Adobe derived much of its revenue from licensing these RIP implementations to printer and imagesetter makers.

Early RIPs were physical hardware: electronic racks that received page descriptions over interfaces such as RS-232 and drove phototypesetters and imagesetters, often maintaining compatibility with older typesetting codes. PostScript Level 2 (1991) added, among other improvements, support for in-RIP color separations and in-RIP image decompression, moving more prepress work into the RIP itself. As general-purpose processors grew faster, RIPs migrated increasingly into software and into printer firmware.

What problem it solved

Before device-independent PDLs and RIPs, page content was typically tied to the specific capabilities and resolution of a given output device. A RIP-plus-PDL architecture addresses several problems at once:

• Device independence: A document is described once, abstractly (curves, text, images, color), and any RIP can render it to whatever resolution and marking technology its device uses.
• Resolution scaling: The same file can be rendered at a few hundred dpi on an office laser printer or at thousands of dpi on a platesetter, because rasterization happens at the RIP, sized to the device grid.
• Consistent type and vector rendering: Font outlines and vector paths are converted to the device grid by one authoritative engine, giving repeatable results.
• Continuous-tone to bilevel conversion: Most marking engines can only place a dot or not place one. The RIP performs the halftoning that lets bilevel devices simulate continuous tone.

How it works

A raster image processor is a component that produces a raster image, also known as a bitmap, from an input page description that may contain raster and/or vector graphics. Its work is classically described in three stages, the first two of which are frequently interleaved in real systems:

1. Interpretation — The page-description language is parsed and translated into an internal representation of each page. Pages are typically processed serially, with the machine state reset between pages. 2. Rendering — The internal representation is converted into a continuous-tone bitmap (multiple bits per pixel), placing text outlines, vector fills, and images onto the device's pixel grid. Color-space conversion generally happens here, before screening. 3. Screening (halftoning) — The continuous-tone bitmap is reduced to the small number of levels the marking engine supports (often one bit per colorant) by halftoning.

Two families of screening are used:

• AM (amplitude-modulated) screening: dots sit on a regular grid and dot size varies with tonal density.
• FM (frequency-modulated / stochastic) screening: dot size is constant and dots are distributed pseudo-randomly, their frequency varying with density.

A RIP has a matrix grid at the resolution of the output device and computes which spots on the grid are turned on and which are turned off. A common Nyquist-derived sampling guideline for source images feeding an AM screen is that the required PPI is roughly 2 times the halftone line screen (LPI) at final size (for example, a 175 LPI screen calls for about 350 PPI image data); this is a rule of thumb rather than a formal standard.

Where it sits in the print/document pipeline

The RIP sits between content creation/prepress and the marking engine:

application (layout, design) → export to PDL (PostScript / PDF / XPS) → RIP (interpret → render → screen) → device raster → marking engine (laser, inkjet, platesetter) → physical output.

In prepress it also commonly supports trapping, imposition, color management and separations, and overprint handling before the screened bitmap is sent to an imagesetter or computer-to-plate (CTP) device.

Relationship to printers

Every raster marking device needs rasterized, device-resolution data, so a RIP is effectively required somewhere in the chain. Its placement varies:

• In-printer firmware RIP: Common for PostScript and PCL office and production laser printers, where a processor inside the printer interprets the incoming PDL. Every PostScript printer contains an embedded RIP.
• Software RIP on a host or server: The bitmap is computed on a computer and sent to the engine; common for large-format inkjet, wide-format, textile, and production digital presses.
• Dedicated hardware RIP: Historically used for high-end typesetting and imagesetting, and still used in some high-throughput prepress environments.

Output-device resolutions the RIP targets range, as illustrative figures, from roughly 600 to 1,200 spots per inch for inkjet and electrophotographic engines up to about 2,000 to 3,000 spots per inch for laser plate and film imaging.

Relationship to operating systems

The RIP is normally invoked through the operating system's print path rather than being part of the kernel:

• On Unix/Linux and macOS, the CUPS printing system commonly uses Ghostscript (a PostScript/PDF interpreter and RIP) or a printer-specific RIP as a filter to convert PDL or PDF into device raster.
• On Windows, the print pipeline has historically used PostScript and PCL drivers alongside the XPS-based path; XPS is one of the PDLs a RIP may accept.
• Ghostscript and related engines are widely used open-source software RIPs; commercial software RIPs also exist for production and large-format work.

The operating system supplies the print spooler, driver, and color-management plumbing; the RIP is the stage that actually rasterizes.

Relationship to PDF / PostScript / drivers

• PostScript: A PostScript interpreter is a RIP in the classic sense: interpreting the PostScript program yields the device dots. This is why the terms "PostScript interpreter" and "PostScript RIP" are used interchangeably.
• PDF: PDF is a page-description format derived from the PostScript imaging model but is not a full programming language. Modern RIPs interpret PDF directly (PDF/X is the prepress-standard exchange form), and many production workflows are now PDF-native end to end.
• Drivers: A printer driver generates the PDL or raster stream and exposes device options; the RIP consumes that stream and produces the final bitmap. In office printers the driver-plus-firmware-RIP split is common; in production, a software RIP often subsumes much of the driver's role and adds color management, screening, and imposition control. Functionally the RIP is the rasterizing engine, not merely a driver.

Modern use

RIPs remain central to essentially all raster printing:

• Production and commercial print: color separations, trapping, screening, imposition, and CTP output.
• Large-format and wide-format inkjet: dedicated software RIPs manage color, ink limits, and media profiles.
• Digital presses (xerographic and inkjet): RIPs convert PDF and PostScript jobs into press-ready raster for on-demand production, controlling halftoning, separation, and resolution.
• Office printing: firmware RIPs inside PostScript and PCL printers, and host-based software RIPs such as Ghostscript via CUPS.

Adobe continues to license print-engine and RIP technology to device manufacturers.

Advantages

• Device- and resolution-independent content that renders correctly across many engines.
• High-quality, repeatable rendering of type, vectors, and images from one authoritative engine.
• Centralized control of color separation, screening/halftoning, trapping, and overprint.
• Enables bilevel marking engines to reproduce continuous-tone imagery.
• Software and firmware implementations scale with general-purpose CPUs.

Limitations

• Rasterization is computationally intensive; complex pages, transparency, and high resolutions can be slow, and "RIP time" is a real production concern.
• Output is device-specific once screened, so a screened bitmap is not freely portable across devices.
• Screening choices (AM vs FM, angles, dot shapes) require expertise; poor settings can cause moiré or banding.
• Correct results depend on accurate color management and device profiles.
• Historically, font-format and PDL-version incompatibilities could cause rendering differences, an issue reduced by standardized exchange formats such as PDF/X.

Related standards and protocols

• PostScript — Adobe page-description language and interpreter model.
• PDF / PDF/X — page-description format; PDF/X is the prepress exchange standard.
• XPS — XML Paper Specification page-description format.
• PCL — Hewlett-Packard Printer Command Language, handled by PCL RIPs.
• Halftoning / screening methods — AM (amplitude-modulated) and FM (stochastic) screening.
• CUPS and Ghostscript — the common software RIP path on Unix-like systems.
• CTP / imagesetting workflows that consume RIP output.

Timeline

1. c. late 1970s–early 1980s

   Work at Xerox PARC on the Interpress page-description language establishes the device-independent PDL concept that leads to PostScript.

2. 1982

   John Warnock and Charles Geschke found Adobe Systems.

3. 1982–1984

   PostScript developed at Adobe by Warnock, Geschke, Brotz, Taft, and Paxton.

4. 1984

   PostScript released; PostScript interpreters function as raster image processors.

5. January 23, 1985

   Apple LaserWriter announced, the first printer to ship with PostScript, catalyzing desktop publishing.

6. 1980s

   Adobe derives much of its revenue from licensing PostScript RIP implementations to device makers.

7. 1991

   PostScript Level 2 introduced, adding in-RIP color separations and in-RIP image decompression, among other improvements.

8. Later era

   RIPs migrate from dedicated hardware into software and printer firmware; PDF and PDF/X increasingly used as the native RIP input in production workflows.