What is a RIP in printing?

A PDF is a set of instructions: draw this curve, set this text in this font, place this image here. Neither a platesetter nor a digital press can act on instructions. Both work in dots, at resolutions far higher than screen — so something has to interpret the instructions and produce the dot map. That is the RIP.

Along the way it does the work that makes the file printable: it applies the colour separations, resolves transparency and overprint settings into what will actually be laid down, and applies the screening. Two RIPs given the same file can produce subtly different results, which is one reason a proof produced on the same workflow as the production run is more trustworthy than one produced elsewhere.

It is also where trouble surfaces. A corrupt embedded font, an image with an unusual colour profile, a transparency effect flattened badly by the design application — all of these tend to appear at the RIP rather than earlier. Which is exactly why ripping happens before plates are made rather than after: a file that fails here has cost nothing but time.

For a buyer, the useful implication is that the PDF you approve and the plate that gets imaged are not quite the same object, and that is why we proof from the ripped file rather than from the original artwork.