![]() ![]() The data must refresh the charge on the drum after each print in order to pick up new toner. The data for each colour must be synchronized for simultaneous delivery. Each colour in the printer has a separate raster image that charges the drum in the right spot to attract that colour of toner to that exact location. An electophotographic (Xerox) printer usually has a resolution similar to an inkjet printer and utilizes a similar RIP process to change a grid of electrostatic charges to positive or negative on an electrostatic drum that is the maximum media size the machine can image. Most inkjet engines have a resolution between 600 and 1,200 spots per inch - so the matrix grid is smaller - but if it is an eight-colour printer, the data for all eight nozzles must be synchronized and delivered simultaneously. An inkjet printer uses the same RIP process to deliver the same one-bit data to each inkjet nozzle for each colour of ink in the printer. A printing plate for flexographic print production is created by turning a laser on and off at a slightly lower resolution. ![]() If the image fills a typical sheet-fed press, it is (30 inches x 3,000 lspi) x (40 inches x 3,000 lspi) = 1.08 trillion, which takes 10 gigabytes of computer memory to store and transfer. The RIP calculates all the spots that must be turned ‘on’ to create the graphic that will be imaged on the printing plate. Most plate-setters have a resolution of 2,000 to 3,000 lspi (laser spots per inch). With computer-to-plate technology for lithographic printing plate production, a laser is used to expose an emulsion on a printing plate. The grid then acts as a switch to turn a mechanical part of the imaging engine on or off. The spots on the grid can only be turned on or off - which is how binary data is encoded - either as 0 or 1. The RIP has a matrix grid at the resolution of the output device and computes which spots on the grid get turned on and which are turned off to create the shape of that letter A on the output device. A font file delivers PostScript language to the RIP that describes a series of points and vector curves between those points to outline the letter A. ![]() Let’s examine the creation of a single character of the alphabet, or glyph. The raster image processor (RIP) is the core technology that does the computational work to convert the broad range of data we use to create a computer graphic into the one-bit data that drives a physical imaging device. ![]()
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