Bit
The smallest unit of computing information.

Bit depth (1-bit, 8-bit, 24-bit)
The amount of information (black and white or color) a computer can discern for each bit of an image. 1-bit is black and white (off or on), 8-bit is 256 "shades", "values" or "levels" of gray or 256 colors, 24-bit is millions of colors.

CD-ROM (Compact Disc-Read Only Memory)
A storage disk for computer files; a CD-ROM can hold about 650 megabytes of data; you cannot replace the information on a CD-ROM as you can on a floppy disk or hard disk.

Crop
To select out an area of an image. Once an image is cropped, save the cropped version with a different name, retaining the original image.

Digital image
A computer file which, when used in conjunction with the proper software, will display a picture on the computer screen or print out to a digital device such as a laser printer.

Dither
a way of arranging the dots in a digitized image that creates an optical illusion of more continuous colors or gray tones than the computer or device can actually display or print.

Download
To "get" a file; to move a file electronically from one place (such as a Web page or server) to your machine (such as onto your hard drive or floppy disk).

Downsize
To reduce the file size of an image, by lowering the resolution and/or reducing the square measurement of the file.

Dpi (dots per inch)
Measure of resolution for a laser printer.
See also: Ppi (pixels per inch)

File format
The specific way digital information is made and stored by the computer. Not all software applications can read and/or manipulate all file formats. (See: GIF, JPEG, TIFF.)

GIF (Graphics Interchange Format)
A common graphic file format on the World Wide Web; used by online services and Web browsing software, GIFs contain information compressed into a relatively small file size and may display faster than other formats.

Grayscale
A system of displaying images in gray tones (or "levels of gray"), simulating the continuous gray tones of a photograph. To achieve grayscale, a monitor must be able to display 2 to 16 bits of information per pixel. This allows the monitor to display a black or white pixel as well as several values between black and white.

Image file size
The amount of computer storage space a file requires; usually measured in kilobytes (K) or megabytes (M, MB, mgs or "megs"). An image file that is 5 x 7 inches, 8-bit gray (as in a black and white photo), resolution 300dpi, is 3M in size. (A floppy disk holds 1.3M.)

Image size
The physical dimensions of the image as measured in the small squares (pixels) of a computer screen; an image filling a "typical" computer screen (13 inch diagonal) would be 640 x 480 pixels; compare to image file size above.

JPEG (Joint Photographic Experts group)
Pronounced "JAY-peg", a graphic file format that compresses information about many colors (up to 16 million) in the image into a smaller file

Line art
Black and white art, usually some type of line drawing (such as that produced by pen and ink).

"Manipulate the image"
Change the image electronically in some way—resize, change the resolution, remove color, sharpen, clean up, edit, convert the file format, etc.

Output resolution
The detail and clarity (achieved by closeness of dots) with which the image will be displayed or printed (dependent on the capability of the display or printing device).

Photoshop
Software developed by Adobe, which allows manipulation and editing (enhancing, resizing, cropping, etc.) of digital images.

Platen
The glass surface of a flatbed scanner.

Ppi (pixels per inch)
Measure of resolution for a monitor.
See also: Dpi (dots per inch)

Resize
To change the size of an image by reducing or increasing the resolution and/or the square measurement of the file. [Note: it is not possible to add more data to an image after it is scanned. It is always preferable to scan an image at the size needed rather than to try to increase the size or resolution later.]

Resolution
An expression of image size; the sharpness and clarity of an image, achieved by the closeness of the dots that make up the image. Resolution is expressed for the scanner as samples per inch (spi), for the screen as pixels per inch (ppi), for the printer as dots per inch (dpi). Most people say "dots per inch" when speaking of scanning resolution, (although technically this is not accurate). The more data per inch (samples, pixels, dots) the higher the resolution of the image and the better looking the image will be. Most screens display at a resolution of 72 pixels per inch. Most laser printers print at 300 or 600 dpi. Higher resolution image files are much larger than low resolution image files, so only save a high resolution image if you need to (such as for archiving). You will need a high resolution image if you are going to print the image in a paper publication and/or enlarge all or any part of the image on screen or on paper.

Scanner
A device that takes a picture of an image, breaks it down into dots and records it as a digital file for use with a computer. Some types of scanners are:

• flatbed scanner: A device for converting paper images (photographs, drawings, printed images) into computer graphic files.
• slide scanner: A device for converting 35mm slides into computer graphic files.

Server
A computer on a network that can be accessed by other computers on the same network; a server can hold software for several people to use and/or space for people to save and access files.

Size (see "Image file size")

TIFF (Tagged Image File Format)
A type of graphic file format developed for scanning. TIFFs are bitmapped graphics that can contain lots of information about each bit or pixel. TIFFs can be read by both Macintosh and PC/Windows applications, such as PageMaker and QuarkXpress. If you think you will ever print your image in a book or publication of any kind, you will want to save a copy of your image as a TIFF. Because TIFFs save a lot of information about each pixel, they can be very large files.

Value
The lightness or darkness of a gray or a color. The darkest level or value of gray is black and the lightest level of gray is white.