Glossary


Image Color Terminology

The terminology for image formats can be confusing because there are often several ways of describing the same format. This topic explains what the terms mean.

24 Bits per Pixel

It is also called a 24-bit image, a true color image, or a 16M color image. Sixteen million is roughly the number of different colors that can be represented by 24 bits, where there are 8 bits for each of the red, green, and blue (RGB) values.

8 Bits per Pixel

It is also called an 8-bit image or a 256-color image. Two hundred fifty-six is the number of different colors that can be achieved by using the image data as 8-bit indexes to an array of colors called a palette.

7 Bits per Pixel

It is also called a 7-bit image or a 128-color image. One hundred twenty-eight is the number of different colors that can be achieved by using the image data as 7-bit indexes to a palette.

6 Bits per Pixel

It is also called a 6-bit image or a 64-color image. Sixty four is the number of different colors that can be achieved by using the image data as 6-bit indexes to a palette.

5 Bits per Pixel

It is also called a 5-bit image or a 32-color image. Thirty two is the number of different colors that can be achieved by using the image data as 5-bit indexes to a palette.

4 Bits per Pixel

It is also called a 4-bit image or a 16-color image. Sixteen is the number of different colors that can be achieved by using the image data as 4-bit indexes to a palette.

3 Bits per Pixel

It is also called a 3-bit image or a 8-color image. Eight is the number of different colors that can be achieved by using the image data as 3-bit indexes to a palette.

2 Bits per Pixel

It is also called a 2-bit image or a 4-color image. Four is the number of different colors that can be achieved by using the image data as 2-bit indexes to a palette.

1 Bit per Pixel

It is also called a 1-bit image, a black and white image, a 2-color image, or a bitonal image. Two is the number of different colors that can be achieved by using the image data as 1-bit indexes to a palette. The palette can contain colors other than black and white, although black and white are most common.

Grayscale

If an image is grayscale, its red, green, and blue values are all the same, and the values are incremented from the lowest to the highest. For example, an 8-bit grayscale image has 256 shades of gray, with values from 0 to 255.

BMP

Windows or OS/2 Bitmap: The image format Microsoft created for use in Windows.

JPG, JPEG, JPE

Joint Photographic Experts Group: 24-bit support and fine compression make this format another standard for publishing on the Web.

GIF

Graphics Interchange Format: The format created by CompuServe for the faster exchange of graphics over modem lines; widely used in Web publishing.

PNG

Portable Network Graphics: A format that combines the bets qualities of GIFs and JPGs; used for Web publishing.

TIF, TIFF

Tagged Image File Format: a widely used raster format jointly supported by Microsoft and Aldus; used mostly in desktop publishing; can be viewed on both Macs and PCs; this is the format used by most fax machines.

TGA, TARGA, TAR, PIX

Truevision Advanced Raster Graphics Adapter (TARGA): Format by Truevision, Inc, used to support image capturing; used with a series of high-resolution graphics adaptors released under the TARGA name.

PCX, PCC

PC Paintbrush format from ZSoft Corporation. These images are used by many word-processing and desktop publishing tools.

JPEG 2000, JP2

JP2 is the file extension for the new image format called JPEG2000 based on state-of-the-art wavelet compression. The JPEG2000 architecture advances a number of different applications in the digital imaging market, everything from digital cameras, pre-press, medical imaging and other key sectors.

PDF

Portable Document Format (PDF). PDF was developed by the Adobe Corporation to allow the exchange and viewing of electronic documents easily and reliably, independent of the environment in which they were created. This format lets you compress large documents to a size small enough to download very quickly. It is also becoming a powerful format for reproducing documents over the web.