Editing Laser printing (section)

===Raster image processing===
The document to be printed is encoded in a page description language such as PostScript, [[Printer Command Language]] (PCL), or [[Open XML Paper Specification]] (OpenXPS). The [[raster image processor]] (RIP) converts the page description into a [[bitmap]] which is stored in the printer's raster memory. Each horizontal strip of dots across the page is known as a [[raster scan|raster]] line or [[scan line]].

Laser printing differs from other printing technologies in that each page is always rendered in a single continuous process without any pausing in the middle, while other technologies like [[inkjet printing|inkjet]] can pause every few lines.<ref name="Ganeev">{{cite book |last1=Ganeev |first1=Rashid A. |title=Laser - Surface Interactions |date=2014 |publisher=Springer Science+Business Media |location=Dordrecht |isbn=978-94-007-7341-7 |page=56 |url=https://books.google.com/books?id=H8DEBAAAQBAJ&pg=PA56 |access-date=15 June 2020}}</ref> To avoid a [[buffer underrun]] (where the laser reaches a point on the page before it has the dots to draw there), a laser printer typically needs enough raster memory to hold the bitmap image of an entire page.

Memory requirements increase with the square of the [[dots per inch]], so 600 dpi requires a minimum of 4 megabytes for monochrome, and 16 megabytes for color (still at 600 dpi). For fully graphical output using a page description language, a minimum of 1 megabyte of memory is needed to store an entire monochrome [[Letter (paper size)|letter]]- or [[A4 paper|A4]]-sized page of dots at 300 dpi. At 300 dpi, there are 90,000 dots per square inch (300 dots per linear inch). A typical 8.5 × 11 sheet of paper has {{convert|0.25|in|mm|adj=on}} margins, reducing the printable area to {{convert|8.0|x|10.5|in|mm}}, or 84 square inches. 84 sq/in × 90,000 dots per sq/in = 7,560,000 dots. 1 [[megabyte]] = 1,048,576 bytes, or 8,388,608 bits, which is just large enough to hold the entire page at 300 dpi, leaving about 100 kilobytes to spare for use by the raster image processor.

In a color printer, each of the four [[CMYK]] toner layers is stored as a separate bitmap, and all four layers are typically preprocessed before printing begins, so a minimum of 4 megabytes is needed for a full-color letter-size or A4-size page at 300 dpi.

During the 1980s, memory chips were still very expensive, which is why entry-level laser printers in that era always came with four-digit suggested retail prices in US dollars. The primitive microprocessors in early [[personal computer]]s were so underpowered and insufficient for graphics work that attached laser printers usually had more onboard processing power.<ref name="Pfiffner_Page_53">{{cite book |last1=Pfiffner |first1=Pamela |title=Inside the Publishing Revolution: The Adobe Story |date=2003 |publisher=Peachpit Press |location=Berkeley |isbn=0-321-11564-3 |page=53}}</ref> Memory prices later decreased significantly, while rapid improvements in the performance of PCs and peripheral cables (most importantly, [[SCSI]]) enabled the development of low-end laser printers which offload rasterization to the sending PC. For such printers, the operating system's print spooler renders the raw bitmap of each page into the PC's system memory at the target resolution, then sends that bitmap directly to the laser (at the expense of slowing down all other programs on the sending PC).<ref name="Brownstein">{{cite journal |last1=Brownstein |first1=Mark |title=SCSI may solve printer data bottlenecks |journal=InfoWorld |date=November 18, 1991 |volume=13 |issue=46 |pages=25–28 |url=https://books.google.com/books?id=Bj4EAAAAMBAJ&pg=PA25 |access-date=July 8, 2023}}</ref> The appearance of so-called "dumb" or "host-based" laser printers from [[NEC]] made it possible for the retail cost of low-end 300-dpi laser printers to decrease to as low as US$700 by early 1994<ref name="Troast">{{cite news |last1=Troast |first1=Randy |title=Low-cost laser printers |url=https://books.google.com/books?id=DTsEAAAAMBAJ&pg=PA85 |work=InfoWorld |date=March 21, 1994 |pages=68–69, 84–85}}</ref> and US$600 by early 1995.<ref name="Grotta">{{cite news |last1=Grotta |first1=Daniel |last2=Grotta |first2=Sally Wiener |title=SuperScript 660: NEC's Dumb Printer Is a Smart Buy |url=https://books.google.com/books?id=eMKimy4DFaEC&pg=PA50 |work=PC Magazine |date=March 28, 1995 |page=50}}</ref>  In September 1997, HP introduced the host-based LaserJet 6L, which could print 600 dpi text at up to six pages per minute for only US$400.<ref name="Mendelson">{{cite news |last1=Mendelson |first1=Edward |title=A New LaserJet Jewel: HP LaserJet 6L makes 6-ppm printing an affordable venture |url=https://books.google.com/books?id=eJVnzcZC5I0C&pg=PA68 |access-date=July 8, 2023 |work=PC Magazine |date=September 9, 1997 |page=68}}</ref>

1200 dpi printers have been widely available in the home market since 2008. 2400 dpi electrophotographic printing plate makers, essentially laser printers that print on plastic sheets, are also available.