Creating color accurately on paper has been one of the major areas of research in color printing. Like monitors, printers closely position different amounts of key primary colors which, from a distance, merge to form any color; this process is known as dithering.
Monitors and printers do this slightly differently however because monitors are light sources, whereas the output from printers reflects light. So, monitors mix the light from phosphors made of the primary additive colors: red, green and blue (RGB), while printers use inks made of the primary subtractive colors: cyan, magenta and yellow (CMY). White light is absorbed by the colored inks, reflecting the desired color. In each case, the basic primary colors are dithered to form the entire spectrum. Dithering breaks a color pixel into an array of dots so that each dot is made up of one of the basic colours or left blank.
The reproduction of color from the monitor to the printer output is also a major area of research known as color-matching. Colors vary from monitor to monitor and the colors on the printed page do not always match up with what is displayed on-screen. The color generated on the printed page is dependent on the color system used and the particular printer model; not by the colors shown on the monitor. Printer manufacturers have put lots of money into the research of accurate monitor/printer color-matching.
Modern inkjets are able to print in color and black and white, but the way they switch between the two modes varies between different models. The basic design is determined by the number of inks in the machine. Printers containing four colors - cyan, yellow, magenta, and black (CMYK) - can switch between black and white text and color images all on the same page with no problem. Printers equipped with only three colors, cant.
Many of the cheaper inkjet models have room for only one cartridge. You can set them up with a black ink cartridge for monochrome printing, or a three-color cartridge (CMY) for color printing, but you cant set them up for both at the same time. This makes a big difference to the operation of the printer. Each time you want to change from black and white to color, you must physically swap over the cartridges. When you use black on a color page, it will be made up from the three colors, which tends to result in an unsatisfactory dark green or grey color usually referred to as composite black. However, the composite black produced by current inkjet printers is much better than it was a few years ago due to the continual advancements in ink chemistry.
Long-time market leader Hewlett-Packard has consistently espoused the advantages of improving color print quality by increasing the number of colors that can be printed on an individual dot rather than simply increasing dpi, arguing that the latter approach both sacrifices speed and causes problems arising from excess ink - especially on plain paper. HP manufactured the first inkjet printer to print more than eight colors (or two drops of ink) on a dot in 1996, it's DeskJet 850C being capable of printing up to four drops of ink on a dot. Over the years it has progressively refined its PhotoREt color layering technology to the point where, by late 1999, it was capable of producing an extremely small 5pl drop size and up to 29 ink drops per dot - sufficient to represent over 3,500 printable colors per dot.
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