Photo Printers - An introduction
In today's digital world, where everything from meetings to marriages are possible with technology, printing quality photos with affordable printers is an option that most of us would like to have. This article will delve into the various characteristics of printers, including the types of printers available for photo printing and some technical know-how as to how they operate.
Today there are specialized photo printers available to do the required task of printing photos. But these specialized printers may not be available to, or affordable by, everyone. Output quality remains the most important issue for photo printers. To print snapshots to give to friends and relatives, most people will be happy with almost any photo printer. But if you want to print the best possible photos to blow up and frame, you'll need to select your printer more carefully. The standard inkjet printers found in most homes does a good job of printing photos, but their quality is not of the highest order. On the other hand, specialized photo printers usually do not work as well on normal tasks, such as word processing, (even if they do, the operation is slower and cost ineffective). The memory of the printer plays a vital role in printing photos. Processing images takes a lot of power, so printers often have as much computing horsepower and memory as a PC. Some printers form the complete image in memory prior to printing it, (doing so speeds things up if the printer has enough memory).
The most important factor is the resolution of the printer. The higher the resolution, the better the printer is. However, this theory cannot be used while comparing inkjet and higher end printers like the dye-sub. For instance, an ink-jet printer with a resolution of 1600 dpi will not give as good a print as a dye-sub printer at 300 dpi. This is due to the fact that each pixel on an ink-jet printer is not a single drop of color, but a cluster of many drops. For ink-jet printers, the size of the small ink drops is more important than the dpi.
The independent printer
Do we still need a computer in order to print our pictures? NO. Not too long ago, the printers had to be connected to enable a computer to print digital images. To go anywhere the image had to first be transferred to the computer. Technological advancements have now made it possible to send images to the Internet, or to a printer, directly from the camera. There are two models for this independence. In the first model the printer has built-in slots which you can plug flash-memory cards. In the second model a device is used to connect the camera to the printer.
The plethora of colors
Color displays use three colors, red, green and blue (RGB) to create color images on the screen. This process is referred to as additive color because adding all three colors together forms white. Color printers use a different process, called subtractive color. This process uses three subtractive primaries, cyan, magenta and yellow. When two of these are overprinted, they form red, green, or blue. When all three are overprinted, they form black. Most printers include a separate black color to provide a deeper black than that formed by combining the primaries. This is useful not only for richer blacks in photographs, but also when printing text. These four colors give the color system its name CMYK (C for cyan, M for magenta, Y for yellow and K for black).
The working of an inkjet printer
It is interesting to note how the inkjet printer works. 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 will determine 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. 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. Since inkjet printing is binary, i.e. they can only put ink down or not put ink down, the gradients of various colors are achieved by one of the two following 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.
High End printers
When quality is the most important criterion for printing photos, one can go for the high-end printers like the dye-subs, (short for dye-sublimation printers). The "dye" in the name comes from the fact that the process uses solid dyes instead of inks or toners. From our primary science classes we may recall that, "Sublimation" is the scientific term for a process where solids, (in this case dyes), are converted into a gas without going through an intervening liquid phase. The quality of pictures printed from a dye-sub are of the highest order and appear as if they had been printed out of a photo-lab.
The working of a dye-sub is different from the inkjet printer. During printing, separate passes are made across the print for each of the four colors, cyan, magenta, yellow and black. 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 the 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 is vaporized controls the density or intensity of the resulting dot on the paper and produces continuous-tone images. 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.
The printer and its third-party associations
Having seen the different printers available for printing photos, we now shift our attention to the printer's allies, the printing ink and the paper. The cost effectiveness of printing photographs is greatly dependent on the ink and the paper costs associated with printing them.
Printer manufacturers develop ink, inkjet cartridges, printers, paper and drivers to work together. Differences in ink chemistry can affect the colors you get, and this is far more likely to degrade a photo than improve it. Differences in the ink's physical properties, such as a change in viscosity, can make a difference in how well the printer controls the drops of ink as they shoot out of the nozzle, (this may also affect image quality).
In the case of inkjet printers, 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.
Conclusion
The four most important things in the context of photo printers are quality, quality, quality and quality. The resolution of the printer is another important factor but, as discussed earlier, this can vary with technology. The paper and the ink quality should also be taken into consideration.
Ideally, output should be waterproof and long-lasting. Most thermal-dye printers lay down a clear over coating to protect the image. Some ink jets also offer waterproof prints. Evaluating each print individually could be the best answer to each of their printing needs. So go ahead, print your favorite photo, blow it up, frame it and hang it in your living room and wait for your friends to be awed by it — then you know that your choice of printer was the right one.
|
