## An Overview of Braille

The Braille system, named after Louis Braille, is a method that is widely used by blind people to read and write. Each Braille character or "cell" is made up of six dot positions, arranged in a rectangle containing two columns of three dots each. A dot may be raised at any of the six positions to form sixty-four combinations, counting the space, in which no dots are raised. For reference purposes, a particular combination may be described by naming the positions where dots are raised, the positions being universally numbered 1 through 3 from top to bottom on the left, and 4 through 6 from top to bottom on the right. For example, dots 1-3-4 would describe a cell with three dots raised, at the top and bottom in the left column and on top of the right column.

The Braille system was based on a method of communication originally developed by Charles Barbier in response to Napoleon's demand for a code that soldiers could use to communicate silently and without light at night called night writing. Barbier's system was too complex for soldiers to learn, and was rejected by the military; in 1821 he visited the National Institute for the Blind in Paris, France, where he met Louis Braille. Louis identified the major failing of the code, which was that the human finger could not encompass the whole symbol without moving, and so could not move rapidly from one symbol to another. His modification was to use a 6 dot cell - the Braille system - which revolutionized written communication for the blind.

## The Braille alphabet

Braille can be seen as the world's first binary character encoding. The system as originally invented by Braille consists of two parts:
1. A character encoding for mapping characters of the French language to tuples of six bits or "dots".
2. A way of representing six-bit characters as raised dots in Braille cell.

Today different Braille codes (or code pages) are used to map character sets of different languages to the six bit cells. Different Braille codes are also used for different uses like mathematics and music.

In addition to simple encoding modern Braille transcription uses contractions to increase reading speed. (See: Grade 2 Braille)

### The Braille cell

Braille generally consists of cells of 6 raised dots arranged in a grid of two dots horizontally by three dots vertically. The dots are conventionally numbered 1, 2, 3 from the top of the leftward column and 4, 5, 6 from the top of the rightward column.

The presence or absence of dots gives the coding for the symbol. Dot height is approximately 0.02 inches (0.5 mm); the horizontal and vertical spacing between dot centers within a Braille cell is approximately 0.1 inches (2.5 mm); the blank space between dots on adjacent cells is approximately 0.15 inches (3.75 mm) horizontally and 0.2 inches (5.0 mm) vertically. A standard Braille page is 11 inches by 11 inches and typically has a maximum of 40 to 42 Braille cells per line and 25 lines.

### Encoding

As originally conceived by Louis Braille, a sequence of characters, using the top 4 dots of the Braille cell, represents letters "a" through "j". Dot 3 is added to each of the "a" through "j" symbols to give letters "k" through "t". Both of the bottom dots (dots 3 and 6) are added to the symbols for "a" through "e" to give letters "u", "v", "x", "y", and "z". The letter "w" is an exception to the pattern because French did not make use of the letter "w" at the time Louis Braille devised his alphabet, and thus he had no need to encode the letter "w".

English Braille codes the letters and punctuation, and some double letter signs and word signs directly, but capitalisation and numbers are dealt with by using a prefix symbol. In practice, Braille produced in the United Kingdom does not have capital letters.

There are Braille codes for representing shorthand (produced on a machine which embosses a paper tape) and for representing mathematics (Nemeth Braille) and musical notation (Braille music).

### Writing Braille

Braille may be produced using a "slate" and a "stylus" in which each dot is created from the back of the page, writing in mirror image, by hand, or it may be produced on a Braille typewriter or "Perkins Brailler", or produced by a Braille embosser attached to a computer. It may also be rendered using other Braille Devices, such as refreshable Braille displays.

Braille has been extended to an 8 dot code, particularly for use with Braille embossers and refreshable Braille displays. In 8 dot Braille the additional dots are added at the bottom of the cell, giving a matrix 4 dots high by 2 dots wide. The additional dots are given the numbers 7 (for the lower-left dot) and 8 (for the lower-right dot). 8-dot Braille has the advantages that the case of an individual letter is directly coded in the cell containing the letter and that all the printable ASCII characters can be represented in a single cell. All 256 possible combinations of 8 dots are encoded by the Unicode standard. Braille with six dots is frequently stored as Braille ASCII.