Raster image processor

A Raster image processor is a part in some printers. The raster image processor receives the data in a description language, like Postscript, PCL, or PDF and changes it to a bitmap or raster image. ^[1]

Raster image processing can be done in two ways: as Software running as part of the operating system, or as a special microprocessor inside the printer. Cheaper printers use a solution called host-based printing, where this is done in the operating system, more expensive printers, and those that support PCL, Postscript or a similar language have a Raster image processor inside the printer.

1. Interpretation: This is the stage where the supported PDLs (Page description languages) are translated into a private internal representation of each page. Most RIPs make pages one after another so the current machine state is only for the current page. They do one page at a time. Once a page has been output the page state is discarded to make the RIP ready for the next page.
2. Rendering: this is how the private internal representation is turned into a continuous tone bitmap. Note that in practical RIPs interpretation and rendering are frequently done together. Simple languages (mostly the most ancient) were designed to work on minimal hardware so tend to "directly drive" the renderer.
3. Screening: In order to print, a continuous-tone bitmap is converted into a halftone (pattern of dots). Two screening methods or types are Amplitude Modulation (AM) screening and stochastic or Frequency Modulation (FM) screening. In AM screening, dot size varies depending on object density -- tonal values; dots are placed in a fixed grid. In FM screening, dot size remains constant and dots are placed in random order to create darker or lighter areas of the image; dot placement is precisely controlled by sophisticated mathematical algorithms.

• RIP Software Definition

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