Online Ascii85 Encoder / Decoder Tool
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Ascii85 (also called "Base85") is a form of binary-to-text encoding developed by Paul E. Rutter for the btoa utility. By using five ASCII characters to represent four bytes of binary data (encoded size 25% larger), it is more efficient than uuencode or Base64, which use four characters to represent three bytes of data (33% increase).
Its main modern use is in Adobe's PostScript and Portable Document Format file formats.
The basic need for a binary-to-text encoding comes from a need to communicate arbitrary binary data over preexisting communications protocols that were designed to carry only human-readable text. They may support only 7-bit ASCII, and within that reserve certain of the ASCII control codes (0–31 and 127) for their own use, may require line breaks at certain maximum intervals, and may do careless things with whitespace. Thus, only the 94 printable ASCII characters are "safe" to use to convey data.
4 bytes (32 bits) can represent 232 = 4,294,967,296 possible values. 5 radix-85 digits provide 855 = 4,437,053,125 possible values, enough to provide for a unique representation for each possible 32-bit value.
32 bits is a popular computer word size, and 85 fits nicely into the 94 available ASCII characters.