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A Guide to Digital Printers

By Kim Brady
Executive Editor

Any computer owner who has shopped around for a desk-top printer knows that there are plenty of options lining the shelves of office supply stores and consumer electronics outlets. There are so many, in fact, that finding the right one for your personal and business needs can be a very daunting task.

How to Determine Print Resolution

You don't need a high-resolution printer to make great pictures. In fact, the higher the printer resolution you use, the more pixels you'll need in your original image file to produce a decent size print. That's because the image file size (in pixels), divided by the printer resolution (in dots per inch), determines the final print size. For example, if the image file size is 1,478 x 1,280 pixels, and you print the file at 163 dpi, the final print size will be 9 x 7.8 inches:

1,478 ÷ 163 = 9.01 and 1,280 ÷ 163 = 7.85, or 9 x 7.8 inches

If your printer resolution is 300 dpi, you'll have higher resolution (more dots per inch laid down on the paper), but you'll also have a smaller print size, because:

1,478 ÷ 300 = 4.92 and 1,280 ÷ 300 = 4.26, or 4.9 x 4.2 inches

So if you decide to invest in a high-resolution printer, make sure that you have the image file sizes to support it.

Fortunately, your search for the perfect printer comes at a time that many consider the "golden age" of printer technology. Prices are down, quality is up, and with a little knowledge and effort, you can turn your home/office computing center into a photo lab, greeting card company, sign maker, and graphic arts department -- all at a price that you'd never dream possible!

Here at Imaging Resource, we know how confusing it can be to decipher all of the features and specifications listed on the outside of desktop printer packages, so we've made a list of critical items you should look for when you go shopping (link to "top ten" list). Print it out, take it with you, and compare features before you buy.

Even before you pick up your car keys, take some time to learn what all those terms and numbers mean. This article is a good start. We've kept it short and simple, so you won't get bogged down in a lot of technical jargon and unnecessary details. Then use our PhotoBot (link to page) search engine for a list of articles and reviews about printers that are currently available on the market. A little time spent surfing online could save you a lot of time fighting traffic on the road!

Image Quality

When you shop for a desktop printer to print your color photographs, what you're really looking for is a model that can deliver photorealistic results. You want your images to look as close to real photographic prints as possible. Photorealistic printers were once very expensive to buy and operate, but technological advancements and competitive pricing have made them much more accessible to the average buyer.

Until recently, high-end (and high-priced) dye-sublimation printers were the only models capable of delivering photorealistic prints, but today's ink-jet printers have made tremendous strides in image quality. Companies like Epson and HP have been aggressively pursuing the professional photography market for years, and the benefits of all their research have finally reached the amateur and serious amateur photographer, with near photo-quality printers starting at less than $100. Look for the term "photorealistic" or "photo-quality" when you shop for a color printer.

Printer Resolution (dpi)

While digital cameras use pixels to measure image resolution, printer resolution is based on the number of dots per inch (dpi) the printer lays down on paper. The higher the dpi, the smaller the dot, and the harder it is to discern one dot from another with normal viewing. Very high-quality, photorealistic ink-jet printers produce dots so small that you can only see them with a magnifying loupe, but there are many levels of acceptable printer quality between high-end and low-end models.

Printer resolutions vary from 300 to 1,400 dpi and higher, depending on the technology used to create the dot (see "Printer Technologies" below) and the size of the nozzles or heating elements in the print head. A printer that delivers 600 dpi resolution is generally considered photo-quality, but there are other factors that influence how a print looks to the naked eye. The kind of paper you use to print the image has a dramatic effect on print quality, as does the number of colors the printer uses, and the way the ink is applied. Read on to find out more about these factors.

How Many Colors?

Most digital printers use a combination of three, four, or six colors to print full-color images. Ink-jet printers dispense each color individually, either from a single chamber in a multi-chambered ink cartridge, or from a single ink cartridge that can be swapped out when one color gets low. Dye-sub printers use heat-transfer ribbons, each dispensing a different colored dye. All printers use cyan, magenta, and yellow -- the three primary colors used in printing -- as their base colors, with a few variations as noted below:

  • Three color printers: Cyan, magenta, and yellow are known as "subtractive" colors. If you combine equal amounts of these three colors, you get black -- the absence of all color. Based on this theory, a CMY printer should be able to produce black without any problem. In the real world, however, CMY blacks usually come out looking muddy or gray, so the printing industry has traditionally added a "composite" black ink to the mix to help clean up the shadows and dark areas of an image. If you want high-quality photos, we recommend that you avoid three-color printers.

  • Four color printers: Like the professional printing presses mentioned above, most high-quality digital printers use a combination of cyan, magenta, yellow, and black (CMYK) inks to recreate -- as closely as possible -- the full spectrum of tones and colors that you see when you take a picture. When shopping for a digital printer, look for one that uses at least four colors.

  • Six color printers: Many printer manufacturers have expanded the traditional CMYK ink set to include two additional colors -- light cyan and light magenta. These two color variations make it easier for the printer to reproduce light-colored image tones, without having to leave excess white space between the ink dots. The result is an image with a more continuous-tone quality.

Ultraviolet Coating

Concerns with print permanency and the adverse effects of UV light have prompted a great deal of research into methods of protecting digital prints. In addition to improvements in ink quality, some printer manufacturers have added a UV coating to the print production process. Originally introduced in high-end, dye-sub printers, the a UV layer may add decades to a print's life expectancy.

Choosing the Right Paper

Paper is a key component to the quality of a digital print. You can't expect to obtain good results from an inexpensive, porous paper that is not designed for printing photo-quality images. Your best bet is to buy papers (and inks) recommended by the printer manufacturer, which in most cases, will be made or marketed by the manufacturer itself. Its papers are optimized for use with its printers, and will probably give you the best results.

Once you become familiar with your new printer, then you can start experimenting with different brands and textures of papers. There are dozens of creative possibilities out there, especially in the realm of ink-jet printing.

Try Before You Buy!

There is no better way to shop for a printer than to try it hands-on. Have a salesperson run a test print, preferably one with text on it. If possible, run the same print on other models you're considering.

Observe the printer in operation. Is it noisy or quiet? Does it take a long time to print? Check the printer's specification sheet, it usually publishes the print speed in prints-per-minute (this time will vary depending on ink coverage and quality setting).

Look at the printed image. On an 8x10-inch print, there should be no visible dots or dithering from a distance of 8 inches. Check to see that the edges of the text are smooth, and that there are no signs of aliasing or stair-stepping along hard edges or lines in the image (straight or diagonal).

Printer Technologies

There are many types of digital color printers on the market. Each approaches the task of depositing ink or dye on paper in a different fashion. The following are the three most common types of printers used for digital color printing. Among them you'll find models priced for the amateur, advanced-amateur, and professional photography markets.

Ink-jet printers operate exactly as their name implies: Ink is sprayed onto the printing substrate through tiny nozzles (about the diameter of a human hair), depositing small droplets of color as they move over the image area. These nozzles are part of a cartridge assembly that makes up the "print head," which passes back and forth across the paper horizontally, squirting ink as it goes along. When one strip of paper is covered with enough ink to form that portion of the image, the printer's "stepper motor" advances the paper to the next strip, so the print head can continue to deposit ink until it has covered the entire sheet of paper.

There are several methods by which ink is transferred from the nozzle to the paper in ink-jet printing. Thermal ink-jet technology, originally developed by Canon U.S.A. as "bubble-jet" printing, uses heat to force the ink through the nozzle openings. Canon has refined the thermal process so that its current bubble-jet printers are capable of producing variable-size dots instead of the uniform size dots that are usually associated with this technology. By varying the dot size, the printers are better able to manipulate ink density. Resolutions for thermal ink-jet printers usually start at 300 dpi.

Micro Piezo technology, a development of Epson America, employs an electrical charge to deliver the ink to the substrate. This method allows more precise control over the size and shape of the ink droplets, which are generally smaller than dots created by the thermal ink-jet process. Smaller dots mean that you can fit more of them per inch, and therefore achieve higher image resolution (typically starting at 720 dpi). Another benefit of the Piezo method is that the ink does not have to stand up to the high temperatures associated with thermal ink-jet technology, so there is more latitude for developing new and improved ink sets.

Hewlett-Packard's PhotoREt III is a color layering technology that produces extremely small droplets, resulting in more colors per pixel than other ink-jet printers (as many as 3,500 printable colors per dot). This allows HP to improve print quality through increased color range, rather than increased dpi. Regardless of which technology they use, ink-jet printers are rapidly becoming the most common color printing devices used in homes, offices, and even graphics businesses -- thanks to constant improvements in performance and significant decreases in price.

Dye-sublimation was long considered the "only" technology capable of producing real photo-quality digital prints. Based on a heat transfer process, thermal dye-sublimation uses thousands of tiny heating elements that come in contact with a "donor ribbon," releasing a gaseous dye that is transferred to the paper one color at a time. Each heating element is controlled individually by electronic impulses from the printer's internal processor. The gaseous nature of the dyes allows them to blend seamlessly on the printing substrate, producing continuous-tone prints that are nearly indiscernible from conventional photographic prints.

Early dye-sub printers were large, bulky, and cost tens of thousands of dollars. Because each color ribbon is processed individually (one pass each for cyan, magenta, yellow, and -- in some printers -- black), the dye-sublimation process can also be somewhat time-consuming. However, the results usually speak for themselves, and some of the newer, less expensive consumer-level dye-subs, like those made by Olympus for use with its digital camera line, are beginning to gain popularity.

Thermo Autochrome
Thermo autochrome is a relatively new printer technology that uses heat-sensitive pigment layers incorporated directly into the paper. The three color layers -- cyan, magenta, and yellow -- are each sensitive to a different temperature. The printer selectively heats areas of the paper, one color at a time, to activate and then fix the pigments with ultraviolet light. Fuji Photo Film U.S.A. uses thermo autochrome technology in its NC and NX printers specifically designed for use as companion printers with its popular line of digital cameras.