|
|
10.2 TYPES OF PRINTERS | ||
 Learn
To Draw |
Learn
To Paint |
Photoshop
Elements |
Animation
Menu |
Art
Principles |
Art
Appreciation |
There are a number of different printer technologies on the market and each has its own niche. In the vast majority of the market right now, the ink-jet printer is king.
Liquid ink-jet printers propel fine droplets of liquid ink toward the surface of paper. In today's marketplace, this technology is the low-cost entry point for personal printing and low-volume color printing.
 |
Tektronix's Phaser 140 is an ink-jet printer. Courtesy of Tektronix. |
These low-cost printers do an amazing job of printing photo-realistic images on a wide variety of papers.
 |
The Epson Stylus 800 is a photo quality ink-jet printer that prints 1440 dots per inch for less than $400. Courtesy of Epson. |
These printers use ink-jet cartridges. Although you can print photos on plain-paper, you'll find that liquid inks tend to soak into the paper taking the color along with them. You'll get richer colors using coated papers that are less absorbent and designed specifically for photographs. The ink dries partly by absorption and partly by evaporation. If the paper is too absorbent, the image looks washed out.
 |
Ink cartridges courtesy of Tektronix. |
A cartridge of ink is attached to a print head with up to hundreds of nozzles, each thinner than a human hair. The number of nozzles and the size of each determines the printer’s resolution. As the print head moves across the paper, a digital signal from the computer tells each nozzle when to propel a drop of ink onto the paper. On some printers, this is done with mechanical vibrations. Piezoelectric crystals change shape when a voltage is applied to them. As they do so, they force ink through the nozzles onto the paper. Each pixel in the image can be made up of a number of tiny drops of ink. The smaller the droplets, and the more of them, the richer and deeper the colors should be.
 |
Piezoelectric crystals force ink through the nozzles onto the paper. Courtesy of Tektronix. |
Inkjet printing, like conventional printing on a press, is binary. These printers can only put ink down or not put ink down. They can’t control the density of each dot. To achieve the illusion of continuous tones, the percentage of area covered by ink is modulated in one or both of two ways:
1. A screening process maps the desired variations in density into variations in dot size. Thus, as the desired density increases, the dot sizes increase and a higher percentage of the white space is covered with ink.
2. If the printing process supports smaller dots of a fixed size, area modulation is achieved by varying the number (rather than the size) of dots that are printed in any given small area.
There are two pitches of concern with such printing: the dot pitch and the screen pitch. For example, an inkjet printer may have a raw dot pitch of 1200 dpi. An equivalent screen pitch may be defined as say, 75 lpi, where "lpi" refers to the equivalent dot pitch of a screen (lines per inch). Thus, each screen cell (75/inch x 75/inch) contains 1200/75 x 1200/75 = 64 raw dots. In such a case, each screen cell could be printed at any of 65 levels (0 to 64 dots). This process would then be equivalent to a 65 level, 75 pixel/inch printer.
At the high end where quality is very important, you’ll find dye-sublimation printers (called dye-subs, but more accurately dye-diffusion). The "dye" in the name comes from the fact that the process uses solid dyes instead of inks or toner. "Sublimation" is the scientific term for a process where solids (in this case dyes) dyes are converted into a gas without going through an intervening liquid phase.
 |
The Phaser 450 courtesy of Tektronix. |
When printing color photographs, there’s nothing like dye sublimation printers. These printers produce photo-realistic continuous-tone images that look like they came from a photo lab.
Dye sub printers have their colored dyes in a transfer roll or ribbon. This roll contains consecutive page-sized panels of cyan, magenta, yellow and black dye. (A three-color transfer roll produces blacks that are a composite of CMY but they are not as rich.) These printers require special paper that's designed to absorb the vaporous dye on contact. Cost per page is high, $3 to $4 dollars for a letter sized page.
 |
Tektronix offers three high-quality transfer rolls for the Phaser 450. Each roll consists of page-sized panels of ink that are passed over a tightly focused heating element and diffused onto dye sublimation paper or transparency film. Courtesy of Tektronix. |
During printing, separate passes are made across the print for each of the four colors—cyan, magenta, yellow, and black. (Maintaining accurate registration for each color requires precise paper feeding one reason these machines are costly.) A thermal print head, consisting of thousands of heating elements, contacts the media being printed on and vaporizes the solid dyes. The resulting gas diffuses into the surface of the paper. What makes these printers unique is that the heating elements on print head can be set to any one of 256 temperatures. The hotter the temperature, the more dye is transferred to the paper. This precise control of the amount of dye that's vaporized controls the density or intensity of the resulting dot on the paper and produces continuous-tone images.
 |
The hotter the print head, the more dye and denser the pixel. Courtesy of Tektronix. |
A dye-sub printer prints square dots each of which is denser in the center and lighter on the perimeter. By varying the amount of power delivered to the printhead for each dot, the amount of dye transferred to each dot and hence the dot’s density can be varied from no dot at all, to a small light dot, up to a large dense dot. Because the size of the dots doesn’t change, the colored parts of the smaller dots have white space between them. At higher energies, the colored areas of each dot become larger and denser, eventually merging into the adjacent dots.
Because the dyes are transparent, a cyan dot may be printed on top of a magenta dot to make a blue dot. By varying the amount of C, Y, and M, any color within the printer's color gamut may be produced.
Black (K) is normally used in these printers only for text, although it may sometimes be used within a continuous-tone (contone) image via the process known as "undercolor removal." (Calculating how much cyan, magenta, and yellow from the image and how much black to add to it.)
Because they can vary the density of each color, dye-sub printers are the only ones that don't have to use halftoning or dithering to create a wide range of colors. And because there are no dithered dot patterns, the colors are applied in a continuous tone; hence the photorealistic images.
 |
Courtesy of Tektronix. |
Despite their name, most dye-sub printers actually work by dye diffusion, not by sublimation. Early in the development of these printers it was mistakenly believed that the dyes were transferred by sublimation. However, the dyes are actually transferred by diffusion from the ribbon to the media. This diffusion is activated by two processes; heat from the printhead and pressure in the printing region. Springs or weights force the printhead to push the inked ribbon into contact with the media, so that diffusion can occur. A more accurate term for this process is actually "Dye Diffusion Thermal" or "D2T" printing. There are some high-end printers such as Kodak's "Approval" system, which do work by sublimation. These printers use a laser to vaporize the dye, which then deposits itself on the media and solidifies. Such printers are the exception rather than the rule, and are capable of very high dot pitch, up to 3000 dpi.
Solid ink-jet printers are great for producing reports and publications with color graphs or other graphics on ordinary paper. They are also the hands-down winner for producing high-quality transparencies at low cost. And, if you're producing a black-and-white document with just a page or two of color charts, you can do so without having to print the charts on a special paper that stands out from the rest of the document.
Solid ink-jet printers produce high-quality images with sharp edges and good color reproduction.
 |
Tektronix's Phaser 300X color printer can handle any paper you'd like: 16-lb. bond to 80-lb. cover. Letterhead, book, text, writing, cover stock, drafting vellum, recycled, or anything else that looks interesting. It's the world's most versatile color printer. Courtesy of Tektronix. |
Cyan, Magenta, Yellow, and Black color sticks (solid bricks—a bit like colored bars of soap) are installed in the printer. Solid ink printers can print on nearly any kind of paper stock, an important feature if you make color proofs. For example; if you are a package designer, you can simulate the appearance of a new design for your client by outputting the proof on the same stock as the final packaging. Solid ink printers work well with colored stock. These printers apply extremely vibrant and opaque color and are ideal for graphics.
  |
Ink sticks courtesy of Tektronix. |
Solid ink-jet printers use solid ink sticks that are melted into a reservoir and sprayed through tiny nozzles onto the page where it immediately hardens. (These are sometimes referred to as phase-change printers because the ink moves from a solid to a liquid phase to be printed then back to a solid phase on the page.) As a final step, the paper moves between two rollers to cold-fuse the image.
 |
Courtesy of Tektronix. |
Thermal-wax transfer was once the workhorse of print technologies, and can still be a very effective technology. Thermal-Wax printers are fast, deliver vibrant colors, are great for printing presentation graphics and the per-page cost is low.
Thermal-wax printing can produce vivid colors on a variety of office laser papers but the quality of continuous tone images does not approach that of dye-sub printers.
Instead of inks, thermal-wax printing uses a transfer roll or ribbon of colored wax that is segmented into page-sized sections each of the three subtractive colors (and optionally, black). The paper is a special paper but you can also use transparency film. Thermal Wax Transfer is one of the most widely used processes in scientific, technical, and business printing.
As the ribbon coated with cyan, magenta, yellow and black wax, in page-sized panels is moved over a thermal printhead, thousands of heating elements on the printhead, capable of precise temperature variations, causes the wax to melt and adhere to specially coated paper or transparency material. The final printed image is composed of tiny dots of colored wax.
 |
Courtesy of Tektronix. |
Laser printers revolutionized black-and-white printing, making graphics and desktop publishing possible. However, color laser printers on on the margins of photographic printing. Not only are their costs high, but their quality has not yet matched the very inexpensive ink-jet printers.
 |
Tektronix's Phaser® 360 Color Printer is the first Adobe® PostScript® 3 color printer. Courtesy of Tektronix. |
Photographs printed on a color laser can be good and the best can rival the photo-realistic images created with dye sublimation printers. The toner is also fairly durable and it's less sensitive to fading from exposure to light than some other technologies.
The colors for laser printing are contained in four separate toner cartridges, one each for cyan, magenta, yellow and black. No special paper is required, but you can use different kinds to change the "look" of the print.
Laser printers use a technology similar to that used in copiers. A laser beam is focused on a photoelectric belt or drum, creating an electrical charge in areas where toner is to adhere. Charged toner is then attracted to those places on the belt or drum. Electrostatic charges cause the toners to adhere to the belt. With black and white printers, this process happens once but with color printers it is repeated for the cyan, magenta, yellow and black components of the image. The image, composed of the four toner colors, is then transferred to a drum which rolls the toners onto the sheet of paper or transparency. The toners on the paper are then fused using either heat or a combination of heat and pressure.
 |
Color laser courtesy of Tektronix. |
Now that you understand a little about how printers work and what your choices are, let's look at some specific printers. These aren't the typical laser, ink-jet, or dye-sub printers you find in stores and catalogs. They are variations on these themes.
The TruPhoto Digital Photo Printer (4" x 6") uses a technology termed Thermo Autochrome. This process uses a thermal head and ultra violet light to process pigments in the paper. There are three layers of colors in the paper, yellow, magenta and cyan. Each color has sensitivity to a temperature. Yellow reacts to a low temperature while cyan reacts to the high temperature and magenta is in the middle. The printer passes the paper past the thermal head 3 times. The first pass heats the yellow layer then the ultra violet light fixes the yellow so that it can no longer be processed. The second pass heats the magenta and the ultra violet light fixes it. The third pass heats the cyan, there is no fixation after the cyan heating. This process is a continuous tone and does not use any other median other than heat, light and TA paper.
- TA prints are permanent and resistant to fading.
- TA paper is the only consumable. Ink jet printers use 4-6 inks released from a jet onto the paper.
- Ink jet printers use dithering Inks can rub off onto another median.
- Dye-sublimation printers use a ribbon to transfer color to the surface and it can be rubbed off
Snapshot printers can use any printing technology but generally makes prints that are smaller than 8 x 10. Many have a lower resolution than their larger cousins. Their prints look good but when placed side-by-side with chemically produced prints, you may notice that they aren't as clear and colorful and yet they cost more than prints. Some of these printers connect directly to cameras so you can bypass the computer altogether.
 |
The Olympus P-300 Personal Photo printer prints 4" x 5.5", 300 dpi, photo-quality dye-sublimation prints in true 24-bit color at a rate of 1.5 minutes per print. Courtesy of Olympus. |
The Fujix Pictrography™ 3000 printer creates silver-halide, 24 bit images with the full depth and richness of a traditional color photographic print. Joel Meyerowitz uses one of these printers.
When it comes to the really high-quality or unusual printer, it's unlikely that you'll want to own one due to the cost. However, there are places that offer digital printing services that you can take advantage of.
In camera stores, you may have seen Kodak Picture Makers. These easy to operate, self-service printers make prints from prints, slides, negatives, photo CD discs, Digital camera memory cards, and JPEG and FlashPix-format floppy diskettes. To do this, the station has integrated drives, scanners, printers, and a display monitor. Before making a print, you can zoom and crop, use red-eye reduction, adjust color and density, and add mattes and borders. You do all of this by making simple choices displayed on a touch-sensitive screen.
 |
The Kodak Picture Maker makes incredible prints from slides, negatives, prints, or digital files. Courtesy of Kodak. |
When you want poster-sized prints, you have to locate a large format ink-jet printer. These printers feed large sheets of paper much like a plotter and the ink-jet printing head lays down lines of ink as the paper passes through the printer. One large format printer from HP prints 2' by 3' images at 600 dpi. Generally you'll find these printers at service bureaus where they'll charge you by the size of the print.
 |
The Tektronix Phaser 600 is a solid ink printer that can print a 34" x 44" print in 12 minutes in Standard mode and 24 minutes in Enhanced mode. Courtesy of Tektronix. |
Iris inkjet printers were originally developed for printing proofs in the printing industry but have been adapted to art uses. Images from these printers have a photo-realistic quality and amazing dynamic range. Using only four ink nozzles, one for each CMYK color, they can print up to 300 dpi in such a way that it visually simulates an 1800 dpi print. They do this by using an 8 x 8 cell for each pixel and an ability to vary the size of each dot placed in that matrix. And color quality isn't their only advantage, they can also print on large, thick material such as heavy artists water-color paper, polyester, cloth, and most other materials that will accept water-base inks. In some corners of the art world, Iris ink-jet prints are called "giclée" prints on the assumption that if it sounds French it sounds like art. However, the term "Giclée" means "squirt or spurt," hardly an art-like term. The first use of this printer for art prints is credited to the rock musician Graham Nash. Nash, working with printmaker Jack Duganne and a friend R. Mac Holbert formed a company called Nash Editions Ltd. in Manhattan Beach, California in 1991. Because of the use of these printers for expensive art prints, a lot of effort has gone into fade-resistant inks and UV protective layers that ensure a print's longevity. How successful these efforts have been, only time will tell.
 |
Iris 3047HS courtesy of Scitex. |
Fiery Color Servers from Electronics for Imaging (EFI) turn standard digital color copiers into networked color printers that produces brilliant, photographic-quality images at an affordable price. You'll find these systems at many service bureaus. These systems are also used to scan photographs and images on the copier, manipulated on your desktop, then printed back via the copier that scanned them. The Fiery XJ+ Color Server has a built-in color management system that gives you control of color from screen to document. Fiery technology is also available as the XJe embedded controller. The XJe is embedded in desktop color laser printers from Canon, Digital and IBM as well as in the new Ricoh Aficio 2000 series digital color copiers.
 |
The Fiery® ZX™ Servers drive high-speed color copiers and black and white digital presses. Courtesy of efi. |
Film recorders, also called film printers, are used to create slides, prints or chromes directly from your desktop.
 |
The Polaroid ProPallete creates 35mm positives and negatives with photographic-quality. Prints with up to 8000 lines of resolution. Courtesy of Polaroid. |