Page 58 - DCAP303_MULTIMEDIA_SYSTEMS

Multimedia Systems

notes If this was to be stored in RAW form, it would need 16 bytes per row for all 10 rows. However
the first two rows are all the same level so it is more efficient to simply save the number of same
colours in a run along with the run colour. The first two rows instead of needing 16 bytes only
need 2 bytes each.
In raw format the first three rows would be
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 1 1 1 1 1 1 1 1 1 1 1 1 0 0
Using run length encoding the first three rows would be
16 0
16 0

2 0 12 1 2 0
While there are more details involved in actual implementations of RLE than described here, this
is the basic principle behind run length encoding. In order for RLE to achieve some degree of
compression there needs to be runs of the same colour, for this reasons it is unlikely to be useful
for highly coloured images such as 24-bit photographs.
The following is a list and brief comments of some specific file formats that are widely used for
saving bitmaps.
format: TIFF (Tagged Image File Format)
platforms: Commonly supported on Mac/DOS-WINDOWS/UNIX
owner: Aldus

Notes: It is almost always supported by major applications that provide bitmap manipulation. The
format consists of items called tags which are defined by the standard. Each tag is followed by a
tag dependent data structure. Supports most colour spaces and compression methods.
format: PCX
platforms: Primarily DOS-WINDOWS

owner: ZSoft Corp
Notes: The oldest and most commonly supported format on DOS machines. Can support indexed
or full 24 bit colour. Run length encoding only.
format: GIF
platforms: Commonly supported on Mac/DOS-WINDOWS/UNIX

owner: CompuServe
Notes: The GIF is a rather under featured but quite popular format. It is used the most on bulletin
boards and on the worldwide internet. It is limited to 8 bit indexed colour and uses LZW
compression can include multiple images and text overlays. Also contains support for layers
and animation.
format: PICT
platforms: Exclusively Mac

owner: Apple

52 LoveLy professionaL University