RIP: How a Page Becomes Dots on a Plate

A page arrives as text, shapes and images, and it leaves the prepress room as a set of instructions a platesetter can expose. The step in between is the RIP, short for raster image processor. It is the software that turns the page into a bitmap the output device can handle.

What the RIP does

An output device cannot draw a curve or scale a font. A RIP reads the page description, whether it comes as PostScript or PDF, and converts every element into a grid of tiny cells. Text is rendered at the machine resolution, images are resampled to the right size and colour space, and vectors are drawn as filled shapes. The result is a raster, one large bitmap of the page.

Screening happens here

The RIP is also where halftones are made. Continuous tone images are converted into dots the press can print, either with a regular grid or a stochastic pattern. Trapping, the slight overlap between colours, is applied at this stage, and so is imposition, the arrangement of pages on a larger sheet. All of it is calculated in the raster before anything is exposed.

One bit or many

A monochrome platesetter needs one bit per pixel, because a plate pixel is either ink or no ink. Proofers and inkjet devices need more, so the RIP delivers the same page in whatever colour space the device expects, CMYK or a wider set for a digital press. The same file can be ripped several times, once for the plate, once for the proof and once for a soft preview.

Where jobs go wrong

Because so much is decided in the RIP, a job can pass the preflight check and still fail here. A missing font is substituted, a low resolution image is scaled up, a transparency flattens the wrong way. When a plate shows a problem the press operator did not create, the answer is often in the settings the RIP used.

A quiet gate

The RIP sits between the designer file and the machine that makes the plate, and it decides how much of the artwork survives the trip. The reputation of book printing is built on advanced manufacturing facilities and strict quality control.