Laser Printer Faults What Pages Should Look Like

Recent laser and inkjet printers come pretty close to providing the ideal look for a text document. High contrast completely black on paper-white printing. Characters should have a well-formed smooth outline corresponding to the abilities of the printer and the settings used for the print job. Areas of black should not contain faded parts.

Do remember that large areas of black are costly to print - a black page with white writing will cost at least 20 times as much as a white page with black writing.

Costs remain an issue. The printer industry has developed a business model where printers are quite costly to make but don't cost much to buy; however the manufacturer expects a revenue stream from cartridges which don't cost much to make but can be sold for high prices.

Photos

Laser printers are good for text and diagrams, they aren't perfect for photographs. There seem to be several reasons:

  • Inkjets can make very small 1 picolitre drops and place them precisely. The electrostatic fields in a laser printer are inherently a bit more random.
  • Neither the inkjet or the laser printer have much greyscale ability - although laser printers may be able to outpace thermal inkjets on this point.
  • Laser printers need an entire page image in memory before they start printing and an A4 greyscale photo could need 128 megabytes of memory - which until recently would have been expensive. Inkjets just use the memory of the user's PC

Most recent laser printers are capable of 1200 dpi print resolution at full speed. Many (not all) have some measure of greyscale. It might be evident but is sometimes overlooked that at 1200dpi the smallest features are less than 1/1000th of an inch (about 1/50th of a millimetre) across. A lot of people have difficulty seeing anything smaller than a fifth of a millimetre and 1200 dpi printers are operating at a tenth this scale. In other words print can have very small features.

Mono laser printers at 1200 dpi may give adequate photographs for things like newsletters and equipment catalogues. But there isn't enough greyscale and resolution combined to match the thousand levels of grey human vision can distinguish. Inkjet printers intended for photographic use overcome this by having special black and grey inks.

Colour

Colour printers use a combination of high resolution, greyscale and dither patterns to give fairly good looking photos. Some Recent laser printers claim an engine resolution of 2400 dpi. However Canon's Pixma series inkjets have 9600dpi resolution and multiple inks so again the inkjet will outperform laser on colour photos.

Laser printers can still win on cost effectiveness. Laser printers don't need the special paper that inkjets use for best photographic effect. Laser printers tend to print at around their rated speed and if they slow down on large photos an increase in memory will normally solve the problem. And laser printers tend to be cheaper to operate - despite the manufacturers aims with cartridge prices.

Memory

As mentioned above one of the limitations on laser printers has always been a need for rather a lot of memory and processing power, a problem inkjets don't entirely share. For instance:

  • An inkjet head sets off from one margin across an 8 inch page printing at 1200 dpi from 100 nozzles. It needs 960,000 bits of data to do that. At the end of the swath the carriage halts for a moment. In principle it could stop for a second or more whilst the printer gets more data from the computer.
  • A laser printer raster scans the whole page. Once the drum and the half-dozen other rollers that provide charges and toner start moving they can't stop, there is too much momentum for them to do so accurately and charges would begin to dissipate. So the laser printer needs the whole page, not just one swath in memory.

In principle an A4 mono page with plain black and printing has 8x1200*11*1200 pixels - something like 126,720,000 of them. If the pixels can just be black and white then that's about 16 megabytes of memory but if there is an element of greyscale it could be as much as 128 MB of RAM. Workgroup printers sometimes ship with that amount. Such a print would be unusual, most pages are just a few kilobytes of material specified as text codes. However bitmapped PDFs (usually scanned from paperwork) can be very large. A duplex network printer can need more memory because whilst one page is printing another will be assembling ready.

Colour printers need about four times as much memory because there are four colour processes. They also need some accuracy in specifying the colours - commonly 8 bits per colour, so the memory demand to have one page printing and another ready to go can be of the order a gigabyte.

Until very recently memories this size were expensive items, more the domain of supercomputers than printers. However that has changed, so whether we will begin to see laser printers boasting higher resolutions because memory has become more affordable reamins to be seen.

print2

Memory Starved Printers.

Because printing at high resolution can use much more memory than smaller and older printers have available, it may sometimes be possible to print a document by cutting the resolution to 300 dpi.

The page here is almost the same but shows a bit of the aliasing effect that happens with low resolution.


The examples shown here are small bitmapped sketches for web use - they are intended to represent what would be seen on a page but they cannot look like a page. The characters shown are just to illustrate what a page might look like - HP use the same pattern and many of our illustrations look like theirs (ours are our own drawings). The illustrations here are imperfect because it's a low resolution screen copy.