Tesseract识别指定字符范围的字符

可以通过配置Tesseract来使用Tesseract进行OCR，opencv和opencv的C#版本Emgu都集成了Tesseract这个工具。

但是在使用时经常会出现误判，比如把“s”识别成“5”，把“1”识别成“l”或“i”。可以设置相应的参数来识别指定范围的字符。

下面是Emgu中关于这个函数的API文档：

Emgu.CV.OCR.Tesseract.Tesseract(string, string, Emgu.CV.OCR.Tesseract.OcrEngineMode, string)

public Tesseract(string dataPath, string language, Emgu.CV.OCR.Tesseract.OcrEngineMode mode, string whiteList)

Member of Emgu.CV.OCR.Tesseract

Summary:

Create an tesseract OCR engine.

Parameters:

dataPath: The datapath must be the name of the parent directory of tessdata and must end in / . Any name after the last / will be stripped.

language: The language is (usually) an ISO 639-3 string or NULL will default to eng. It is entirely safe (and eventually will be efficient too) to call Init multiple times on the same instance to change language, or just to reset the classifier. The language
may be a string of the form [~]%lt;lang>[+[~]<lang>]* indicating that multiple languages are to be loaded. Eg hin+eng will load Hindi and English. Languages may specify internally that they want to be loaded with one or more other languages, so the ~ sign
is available to override that. Eg if hin were set to load eng by default, then hin+~eng would force loading only hin. The number of loaded languages is limited only by memory, with the caveat that loading additional languages will impact both speed and accuracy,
as there is more work to do to decide on the applicable language, and there is more chance of hallucinating incorrect words.

mode: OCR engine mode

whiteList: This can be used to specify a white list for OCR. e.g. specify "1234567890" to recognize digits only. Note that the white list currently seems to only work with OcrEngineMode.OEM_TESSERACT_ONLY

Tesseract tesseract = new Tesseract();

tesseract.Init(path, lang,Tesseract.OcrEngineMode.OEM_TESSERACT_ONLY);//path为语言包路径，lang为语言

tesseract.SetVariable("tessedit_char_whitelist", "0123456789");

上面代码可以实现只识别数字，这样就会大大提高识别的准度。把“0123456789”改成“abcdefghijkmnopqrstuvwxyz”即可只识别出字母。

设置前：