digital photo - a computer file – from a digital camera or scanner – which contains sets of numbers that specify the colors of a rectangular grid of pixels. A digital photo is invisible unless it is displayed or printed.

24-bit color - the colors of the pixels in a digital photo are defined by their red, green and blue (RGB) components. The red, green and blue values range from 0 to 255 (an 8-bit binary number). Hence: 24-bit color = 3 colors x 8-bits per color. Here are a few colors with their RGB components:

a bit of prose on the confusion between dpi and ppi - the terms 'ppi' (pixels per inch) and 'dpi' (dots per inch) are often used in place of one another. For inkjet printers, there is an important distinction. An inkjet printer must put down multiple tiny dots of ink to simulate the colors of each pixel in a digital photo. For example, when printing a digital photo at 360 pixels per inch on a 2880x720 dots per inch printer, the printer may place drops of each ink in 8 distinct locations to produce a single pixel. These definitions are intended to clarify the distinction.

pixels per inch (ppi) - the number of pixels in the length or width of a digital photo divided by the physical length or width of a printed image. The term 'pixels per inch' only has meaning when a digital photo is printed or displayed. This chart shows pixels per inch for digital photos printed at different sizes. See the FAQ section for a discussion of appropriate ppi for printing. top

dots per inch (dpi) - the number of drops of ink per inch that an inkjet printer can place on paper. Typical advertised values are 1440x720 dpi, or 1200x1200 dpi, or 2880x720 dpi, or 4800 dpi, etc. These numbers define a very fine rectangular grid of places for drops of ink to reside in the finished print. top

drop size (or volume) - the size of the smallest individual drops that a printer can produce. The drop size is measured in picoliters (1/1,000,000,000,000 of a liter). Some inkjet printers can vary the drop size. Five years ago a typical drop size was 30 to 50 picoliters; today drop sizes of 2 to 4 picoliters are state-of-the-art. This is comparable to the size difference between a softball and a ping pong ball. Smaller drops produce smoother-looking prints because they make smaller dots on the paper. top

dot size - the size of the dot produced by one drop of ink on paper. The dot size depends on the drop volume and the paper characteristics. Most inkjet papers are coated with clay or polymers to produce small round dots. Plain paper and other uncoated papers generally produce larger dots which are usually not round. More information about types of inkjet paper can be found on the papers page. top

dither- in simplest terms, inkjet printers have either 4 inks (Cyan, Magenta, Yellow, and Black / CMYK) or 6 inks (Cyan, Light Cyan, Magenta, Light Magenta, Yellow, and Black / CcMmYK), yet they print millions of different colors. This is accomplished by applying different numbers of drops of the different color inks as needed to simulate the colors of the pixels. Some printers also vary the size of the ink drops, using larger drops in dark areas and smaller drops in light areas. This scan is a small section of a print from a 4-color inkjet printer. top

printer driver - software provided by a manufacturer to run (drive) a printer. Printer drivers are generally available for different versions of Windows and Macintosh operating systems. Manufacturers provide free updates for printer drivers on their web sites. Updates can fix printing problems and improve print quality, so it is a good practice to check for driver updates every few months. There are links on the printer drivers page for several brands of printers. top

printer driver settings - all printer drivers allow the user to make choices which affect the way that printers put drops of ink on the paper. These choices enable good printing results on a variety of different papers. Driver settings may include paper type, dpi (sometimes called normal-better-best or speed-quality), screening, density, and color controls, etc. Using the wrong printer driver setting for your paper is one of the the most common causes of poor prints. More information on printer driver settings is found on the printer driver settings page. top

print head - an electro-mechanical device which contains an ink feed system, drop formation mechanism, nozzles, and (usually) the ink supply in tanks or cartridges. The print head is moved across the paper to deposit drops of ink in the correct positions. top

In a thermal inkjet printer, the filling chamber for each nozzle has a small resister which rapidly heats the ink forming a bubble. The bubble pushes a drop of ink out the nozzle. Over time, a scum can form on the resister. Thermal print heads are relatively inexpensive. Thermal print heads are either built into the ink cartridges, or the printer might have an easily replaceable print head with refill tanks. Hewlett Packard, Canon and Lexmark printers use thermal technology.
	thermal inkjet drop formation
In a piezoelectric inkjet printer, small walls in the nozzle filling chambers are made of piezoelectric material that changes shape (deflects) when a voltage is applied. The deflection of the walls forces a drop of ink out of the nozzle. Piezo print heads are quite expensive and are built into the printer. Epson printers use piezo technology.
	piezo inkjet drop formation

paper feed - the two basic paper feed paths – top feed typically used by Canon and Epson, and bottom feed used by Hewlett-Packard – are shown in the cross section diagrams, below. A set of pinch rollers is used to feed, correctly position, and securely hold the paper while it is being printed. Top feed printers have a straighter paper path, and can usually handle thicker or stiffer papers. top

pinch rollers - top paper feed	pinch rollers - bottom paper feed

printable area - many inkjet printers cannot print to the edges of a sheet of paper. The non-printable edges – or margins – may be listed in the user manual. These diagrams illustrate typical printable areas for portrait and landscape orientation. The trailing edge of the paper (the last edge out of the printer) usually has a larger margin since the pinch rollers, which hold the paper during printing, need to be some distance from the print head to allow clearance for print head motion. top

typical printable area (landscape)

typical printable area (portrait)