Multimedia (graphics)

Multimedia graphics - bitmap file formats

There are many popular bitmap graphic formats.

These include; BMP (Bitmap), JPG (JPEG), GIF, TIF (or TIFF), DIB.
The graphic application will generally determine the format a graphic will be saved in.
Most formats will allow you to store bitmaps with various colour palettes. Obviously the larger the palette the larger the bitmap. A notable exception is JPG.
Some formats such as the Windows Metafile (WMF) can store a combination of Bitmap and vector, though are generally classified as vector formats.
"Lossy" and "loss-less" formats are used depending on the requirements of the format. A lossy format compresses a file by discarding similar data bits located next to one another in a file. For example, a lossy image of a blue sky will be less detailed since the blue fills most of the area. Generally the data loss isn't detected by the eye. JPG is an example of a lossy format. Successive editing of a lossy image will degrade image quality.(Millman, H. 1999, Mar)

BMP - Bitmap

Most commonly used in Microsoft Windows applications.
Both Red Green Blue (RGB) and Run Length Encoded (RLE) formats.
Storage is extremely inefficient and compression of 8x's and above possible when converted to another bitmap format.
Hence not generally supported in Web Browsers.
A "loss less" format - where successive editing will not degrade image quality.

JPG (JPEG)

Recommended for photographs
From the Joint Photographic Experts Group
Will probably become the "standard" format for bitmap files.
All pictures stored in a 16 million colour format with selectable compression possible.
Lower colour pictures have colours increased when saving in JPG format.
No transparency possible.
Unfortunately successive editing will result in a steady degradation of the image due to the 'lossy' compression technique.

GIF - Graphic image (interchange) format

filled

transparent

The GIF file format allows for transparent GIFs where one of the colours is assigned to be transparent.
This enables a bitmap to "float" over a background, rather than fill a rectangular area.

Recommended for diagrams.
Proprietary format from Compuserve, designed for high compression over a telephone network. Products that edit GIF's, or enable GIF's to be published need to licence the format from CompuServe).
The Standard for bulletin boards and the Internet, and has been around for many years
Has an interlaced option where every odd line is stored, then every even line. This enables a file to be dynamically displayed on the screen, whilst being received via a modem, and if the picture is not what is wanted transmission may be cancelled
Transparent backgrounds possible
GIF 89a also allows for animated GIF's. (See section on animation)

PNG - Portable Network Graphics

WWW consortium to recommendation status (1998)
Improved version of GIF with
- Better compression than GIF/LZW method. Typically, an image in a PNG file can be 10 to 30% more compressed than a GIF file
- 100% lossless compression
- A larger palette and better transparency support. True colour images up to 48 bits per pixel, Grey scale images up to 16 bits per pixel
  48 bits per pixel with up to 48 bits for color or 32 bits for colour.
- Full Alpha channel and transparency support
  16bits for alpha channel (64,000 levels of transparancy per pixel- from opaque to transparent.
- Streamability and progressive display
- Complete hardware and platform independence
- Palette-mapped images to 256 colours
- Supported in Internet Explorer 4.01+ and Communicator 4.04+.
- Does not support multiple images (no animation possible).
- Group42.com (1999 ). Group 42: PNG Info [Online]. Available: WWW URL:http://www.group42.com/png.htm Gibbs,M. (1998, Apr/May)

TIF (TIFF)- Tagged image format

A common file format, unfortunately with several versions - not always guarenteed to work with all your Windows application programs.
TIFF has the lossless LZW compression, Lempel-Ziv-Welch which is the same compression as used by PKZIP, which is generally need both to minimise you file size and to be compatible with files sent to you that have used it.
Commonly used as the format for scanned images where further editing of the image is likely.

FlashPix

Enables an image to be stored at several resolutions. Allows a low resolution image to be viewed on the WWW and if desired a high quality image may be downoaded.