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. Braille 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 encoding scheme for representing the characters of a writing system. 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 a 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. However, because the six-dot Braille cell only offers 64 possible combinations (2⁶ = 64), of which some are omitted because they feel the same (having the same dots pattern in a different position), many Braille characters have different meanings based on their context. Therefore, character mapping is not one-to-one.

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 six raised dots arranged in a grid of two dots horizontally by three dots vertically. The dots are conventionally numbered 1, 2, and 3 from the top of the left column and 4, 5, and 6 from the top of the right 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.Fact: date=April 2008 A standard Braille page is 11 inches by 11.5 inches and typically has a maximum of 40 to 43 Braille cells per line and 25 lines.

Encoding

As originally conceived by Louis Braille, a sequence of characters, using the top four 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".