Multimedia: Images

Lossless

All information from the original file is preserved when compressed.

Bitmap

An image stored as an array of pixel values. Generally used for photos

GIF

GIF = Graphic Interchange Format and it is a bitmap image that saves in a "lossless" format and is best suited for graphs, diagrams and simple animations

JPEG

JPEG = Joint Photographic Experts Group and it is a bitmap image that saves in "lossy" format. it's best suited for photos, computer game screen shots and film stills.

Lossy

Not all information in the original file is preserved; saving this way removes some of the information to keep the file size small which results in a generally unperceivable loss of quality.

PNG

PNG = Portable Network Graphics and is a bitmap image available in either 8 or 24 bit (256 / 16M color) it saves in a "lossless" format and is best suited for line art, text, screenshots of Windows, general web graphics and "comic strip" style art.

Posterization

The effect of too few quantization levels to appropriately represent the sample

Resolution

The number of pixels in an image. Resolution is sometimes identified by the width and height of the image as well as the total number of pixels in the image

Dithering

This is used to avoid posterization as, with compression, some colours may be removed from the colour table; instead of replacing each individual pixel with one of the remaining colours, an area of missing colour would be replaced with a mixture of colours ie: if no pink then a block of 4 pixels would become 2 white + 2 red.

Compression

Used to reduce irrelevance and redundancy of image data in order to be able to store or transmit data in an efficient form.. An uncompressed image is saved in a file format that doesn't compress the pixels in the image at all.

Vector

image is stored as a mathematical description of a collection of lines and shapes. generally used for Logos and clipart