---
name: "unicharambigs"
section: "5"
platform: "linux"
package: "tesseract-ocr"
version: "5.5.0-1+b1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/unicharambigs"
---

# unicharambigs(5)

Tesseract unicharset ambiguities

## NAME

unicharambigs - Tesseract unicharset ambiguities

## DESCRIPTION

The unicharambigs file (a component of traineddata, see [combine\_tessdata(1)](/combine_tessdata/1.md) ) is used by Tesseract to represent possible ambiguities between characters, or groups of characters.

The file contains a number of lines, laid out as follow:

```
[num] <TAB> [char(s)] <TAB> [num] <TAB> [char(s)] <TAB> [num]
```

| | |
| --- | --- |
| Field one | the number of characters contained in field two |
| Field two | the character sequence to be replaced |
| Field three | the number of characters contained in field four |
| Field four | the character sequence used to replace field two |
| Field five | contains either 1 or 0. 1 denotes a mandatory replacement, 0 denotes an optional replacement. |

Characters appearing in fields two and four should appear in unicharset. The numbers in fields one and three refer to the number of unichars (not bytes).

## EXAMPLE

```
v1
2       ' '     1       "     1
1       m       2       r n   0
3       i i i   1       m     0
```

The first line is a version identifier. In this example, all instances of the *2* character sequence *'*' will **always** be replaced by the *1* character sequence *"*; a *1* character sequence *m* **may** be replaced by the *2* character sequence *rn*, and the *3* character sequence **may** be replaced by the *1* character sequence *m*.

Version 3.03 and on supports a new, simpler format for the unicharambigs file:

```
v2
'' " 1
m rn 0
iii m 0
```

In this format, the "error" and "correction" are simple UTF-8 strings separated by a space, and, after another space, the same type specifier as v1 (0 for optional and 1 for mandatory substitution). Note the downside of this simpler format is that Tesseract has to encode the UTF-8 strings into the components of the unicharset. In complex scripts, this encoding may be ambiguous. In this case, the encoding is chosen such as to use the least UTF-8 characters for each component, ie the shortest unicharset components will make up the encoding.

## HISTORY

The unicharambigs file first appeared in Tesseract 3.00; prior to that, a similar format, called DangAmbigs (*dangerous ambiguities*) was used: the format was almost identical, except only mandatory replacements could be specified, and field 5 was absent.

## BUGS

This is a documentation "bug": it’s not currently clear what should be done in the case of ligatures (such as *fi*) which may also appear as regular letters in the unicharset.

## SEE ALSO

[tesseract(1)](/tesseract/1.md), [unicharset(5)](/unicharset/5.md) **https://tesseract-ocr.github.io/tessdoc/Training-Tesseract-3.03%E2%80%933.05.html#the-unicharambigs-file**

## AUTHOR

The Tesseract OCR engine was written by Ray Smith and his research groups at Hewlett Packard (1985-1995) and Google (2006-2018).