UbuntuHelp:OCR
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- title OCR
Parent: UbuntuHelp:Software
目录
OCR - Optical Character Recognition
OCR is a technology that allows you to convert scanned images of text into plain text. This enables you to save space, edit the text and search/index it.
Available OCR tools
The Ubuntu Universe repositories contain the following OCR tools:
- tesseract-ocr
- ocrad
- gocr
Tesseract
Introduction
Arguably the one producing the best (most accurate) results is Tesseract. It is a technology initially developed by HP Labs between 1985 and 1995, then they open-sourced it in 2005. Tesseract can recognize text in 7 different languages: English, German, French, Italian, Spanish, Brazilian Portuguese and Dutch. You can install more than one dictionaries if you need. It does not support layout analysis, so multi-column text, images, equations etc. should give you a garbled text output. Also, it only supports TIFF images as input.
Usage
Tesseract is currently a command-line-only tool (although they're working on an integration with OCROpus for a GUI). After successful installation, the command to use is tesseract <path to tiff image> <output file>. Tesseract will automatically give the output file a .txt extension.
Preparing images for Tesseract
Tesseract is not very flexible about the format of its input images. It will only accept TIFF images. According to user reports, compressed TIFF images are quite problematic, and the same goes for grey-scale and colour images. So you're better of with single-bit uncompressed TIFF images. The process to prepare them with GIMP is very simple:
- Go to the Image→Mode menu and make sure the image is in RGB or Grayscale mode.
- Select from the menu Tools→Color Tools→Threshold and choose an adequate threshold value.
- Select from the menu Image→Mode→Indexed and from the options choose 1-bit and no dithering.
- Save the image in TIFF format.
