Computer Braille primarily works by using an extended system of dots per character compared to traditional literary Braille, specifically an 8-dot system, to represent a wider range of computer-specific characters and data.
Unlike standard literary Braille which uses a 6-dot cell to represent letters, numbers, and punctuation (limiting combinations), computer Braille, often defined by standards like the Braille Computer Notation (BCN) by the Braille Authority of the United Kingdom, utilizes 8-dot patterns.
The 8-Dot System in Computer Braille
The extension from 6 to 8 dots significantly increases the number of unique patterns possible per character.
- 6-dot Braille: Has 2⁶ = 64 possible combinations. Sufficient for letters, numbers, and common punctuation.
- 8-dot Braille: Has 2⁸ = 256 possible combinations.
This increased capacity is crucial for computer use because it allows computer Braille systems to represent every possible value that can be stored in a single byte (ranging from 0 to 255).
Why 256 Values Are Important
Representing 256 distinct values means that arbitrary byte data can be written in Braille. This includes:
- All ASCII characters: Uppercase and lowercase letters, numbers, standard punctuation, and control characters (like Tab, Enter, Escape).
- Extended characters: Characters found in various character sets (depending on the specific encoding being represented).
- Raw data: Potentially non-textual byte values in files.
This capability allows a computer screen's content, including programming code, file names, and special symbols, to be rendered directly in Braille without ambiguity or loss of information.
Compatibility with 6-dot Braille
A key design feature of systems like the Braille Computer Notation (BCN) is that its 6-dot subset is identical to the 6-dot code. This means that the 8-dot representations for standard literary Braille characters (like letters 'a' through 'z') use only the top six dots and are the same patterns found in traditional 6-dot Braille. This provides a degree of backward compatibility and familiarity for users accustomed to 6-dot Braille.
How It's Used
Computer Braille is typically processed by software called a screen reader or Braille translator. This software takes the digital content from a computer screen or file and converts it into the appropriate 8-dot Braille patterns. These patterns are then sent to:
- Braille Displays: Electronic devices that raise and lower pins to form tactile Braille characters on demand, allowing users to read screen content line by line.
- Braille Embossers: Printers that punch the dots onto special paper, creating permanent hard copies of documents in Braille.
By mapping each byte of computer data to a unique 8-dot Braille cell, computer Braille provides a faithful and comprehensive tactile representation of digital information.
