Image Anatomy


digital image \ˈdi-jə-təl • ˈi-mij\:

A representation of an image stored in numerical form, for potential display, manipulation of dissemination via computer technologies (Terras 6). Images are comprised of pixels, and the number of pixels in an image determines the resolution. Images can be saved as various file formats, each of which has its own way of compressing the image's file size.

pixel or picture element:

Any of the small discrete elements that together constitute an image (as on a television or computer screen). (Merriam-Webster) Pixels are ordered as a grid in rows and columns, and each pixel contains numbers representing brightness and color. Typically, projected images should be 1024 x 768 pixels to fill the screen.

pixels

resolution:

A measure of the sharpness of an image or of the fineness with which a device (as a video display, printer, or scanner) can produce or record such an image usually expressed as the total number or density of pixels in the image, a resolution of 1200 dots per inch. (Merriam-Webster)

Images displayed on websites (including this image of a leaf), as well as through classroom projectors typically have a resolution of 72 pixels per inch. No more than that is necessary to display a clear image. However, to print images or to create sharp details, a resolution of at least 300 pixels per inch is reccomended.

file size:

file size

The amount of data in an image file, measured in kilobytes (KB), megabites (MB), and in some cases, gigabytes (GB)

file format:

head shot of a yellow labrador retriever with leaves in the background

Packages of information that can be stored as data files or sent via network as data streams (aka bitstreams, byte streams) (Library of Congress). While there are hundreds of image file formats, some of the most common file formates include JPEG, TIFF, and GIF.

compression:

Reducing the file size of an image. Different file formats use different compression algorithms, which can be catagorized as lossy and lossless. Lossy compression techniques discard information from an image which can never be reconstructed, while lossless compression preserves information to create a compressed image that is identical to the original. Lossless file formats, such as TIFFs, will never be as small as lossy formats such as JPEGs. Formats with lossless compression algorithms are ideal for archival and printing purposes, while lossy formats are ideal for quick and smooth presentations. The two photographs below are .jpegs: one is the original, and the other has been compressed.

close up of bloody mary flowers

original

close up of bloody mary flowers, compressed

compressed