Multimedia graphics - bitmap

A bitmap is a graphic made up of hundreds of coloured dots. A computer screen is a large "bitmap" image with each pixel representing a single dot of the bitmap. Bitmaps images are used in; Photos in a newspaper (look really closely and you'll be able to see the dots) Video where each frame is really a grid of dots Normally a bitmap will fill a "rectangular" area. 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. The application you are using needs to be able to handle transparent gifs, For example, Web Browsers such as Microsoft's Internet Explorer and Netscape Communicator, and Word processing applications such as MS-Word 97.

Bitmap Colours

Each dot in a coloured bitmap is made up of a Red, Green and Blue component. It is possible to have each colour vary in intensity by 0 (Off)-255 (Full on), or for RGB a total of 16 million variations.

• Examples;
  Black (R:0,G:0,B:0), Dark Blue (R:0,G:0,B:128),Lt. Grey (R:192,G:192,B:192),
  Red (R:255,B:0,G:0), White (R:255,G:255,B:255)

Each bitmap is associated with a palette of colours (Combinations of Red, Green and Blue).

Using 4 bits it is possible to store a palette of 16 colours. Windows has standard 16 and 256 (8 bit) colour palettes,

• Typical colour formats;
  2 colours (1 bit), 16 colour (4 bit), 256 colour (8 bit), 32K colours (15 bit), 64K colours (16 bit), 16 million colours (24 bit)

On 16 colour and 256 colour it is usual to use the Windows standard palette to avoid a "palette clash". Unfortunately this will not bring out the best in your graphic. For example a picture of the sea will predominantly be made up of blues whilst a forest greens.

This graphic illustrates a palette clash in Win95 Paint. Note that even the desktop is affected.

Applications

Paintbrush

• Features:
  Comes standard with Window 3.x and Win 95.

PaintShop Pro

Ray tracing

• Uses quite a different technique to produce bitmaps.
• Using mathematical models in 3-Dimensions a "Virutal image" is created. This image is then "Rendered" (filled in) to give lighting effects. Use extensively in animation.

[Rev 06/14/99] 28/5/97 © 1997 V/2-Com (Verhaart), P O Box 8415, Havelock North, New Zealand.