Our Day Has Come

Printing in OS X

How Printers Work All inkjet printers, no matter how big or small, print only raster images -- dots. The same is also true of all PostScript printers and typesetters. These also print only dots. No matter how fine the resolution, or how smooth the lines, the machines are all printing dots. In the past, dot-matrix printers printed the same QuickDraw images you see on your screen. QuickDraw is an integer-based system of whole numbers (no decimals) that Apple came up with to draw images on the screen. It is fast, but it is also limited because it is based on whole-number integers and the square pens that such a system produces. Years ago, Adobe Systems introduced PostScript, which is a resolution-independent page description language that made desktop publishing possible. Images arrived on the paper by a circuitous route. The program drew in integer-based QuickDraw with a square pen. (Some programs, like PowerCADD, achieved a better image by creating a QuickDraw image that was twice as big and then asking the printer to scale it down. That's what High Res printing in PowerCADD has done.) This image was then converted to a PostScript image by Apple's print driver and sent to the PostScript printer as text, in the form of PostScript commands. Inside the printer, a PostScript interpreter received the commands and created a raster image of the page, then put it on the paper. PowerCADD's drawing is stored in 64-bit double-precision numbers, but to print, these had to be converted to integer-based QuickDraw, then to text in PostScript commands, and then interpreted in the printer. While a PostScript printer can easily draw a line with a round pen, to duplicate the image on the screen, Apple's print driver actually created a polygon to reproduce the square pen that we've all hated for so long. In the case of plotter drivers like PowerPlot, Microspot or software RIPs, each simply received the QuickDraw commands and then created a raster image which it sent to the plotter. Even HPGL created a raster image. With OS X, Apple now has its Quartz graphic engine. It is, in effect, PostScript without the language. Like PostScript, it is resolution-independent, and the same routines are used for drawing on the screen and in printing. When you create a PDF file in OS X, the Quartz commands are converted to PostScript, and since Quartz and PostScript are nearly identical, this is a very straightforward process. Gimp-Print works by receiving the PostScript in a PDF file, it uses its own GhostScript interpreter to produce the dots, and then sends this to the printer.) As a result, Gimp-Print makes any dumb printer into a powerful PostScript printer. And it's free.