nnocr
v0.3.6
Published
Native Node.js bindings for the Tesseract OCR project.
Downloads
21
Maintainers
Readme
node-native-ocr
The native Node.js bindings to the Tesseract OCR project using N-API and node-addon-api.
Benefits:
- Avoid spawning
tesseract
command line. - Asynchronous I/O: Image reading and processing in insulated event loop backed by libuv.
- Support to read image data from JavaScript
buffer
s.
Contributions are welcome.
Install
Via npm:
$ npm install node-native-ocr
Usage
Recognize an Image Buffer
import { recognize } from "node-native-ocr";
import fs from "fs-extra";
const filepath = path.join(
__dirname,
"test",
"fixtures",
"node-native-ocr.jpg"
);
fs.readFile(filepath).then(recognize).then(console.log); // 'node-native-ocr'
recognize(image [, options])
- image
Buffer
the content buffer of the image file. - options
node-native-ocrOptions=
optional
Returns Promise.<String>
the recognized text if succeeded.
node-native-ocrOptions
Object
{
// @type `(String|Array.<String>)=eng`,
//
// Specifies language(s) used for OCR.
// Run `tesseract --list-langs` in command line for all supported languages.
// Defaults to `'eng'`.
//
// To specify multiple languages, use an array.
// English and Simplified Chinese, for example:
// ```
// lang: ['eng', 'chi_sim']
// ```
lang: "eng";
}
Promise.reject(error)
- error
Error
The JavaScriptError
instance- code
String
Error code. - message
String
Error message. - other properties of
Error
.
- code
code: ERR_READ_IMAGE
Rejects if it fails to read image data from file or buffer.
code: ERR_INIT_TESSER
Rejects if tesseract fails to initialize
Example of Using with Electron
// For details of `mainWindow: BrowserWindow`, see
// https://github.com/electron/electron/blob/master/docs/api/browser-window.md
mainWindow.capturePage(
{
x: 10,
y: 10,
width: 100,
height: 10,
},
(data) => {
const appPath = (electron.app || electron.remote.app).getAppPath();
const tessdataPath = path.resolve(appPath, ocrPackagePath, "tessdata");
recognize(data.toPNG(), {
lang: ["eng", "ita"],
// output can be 'tsv' or 'txt'
output: "txt",
tessdataPath,
}).then(console.log);
}
);
Compiling Troubles
For Mac OS users, if you are experiencing trouble when compiling, run the following command:
$ xcode-select --install
will resolve most problems.
Warnings:
xcode-select: error: tool 'xcodebuild' requires Xcode, but active developer directory '/Library/Developer/CommandLineTools' is a command line tools instance
resolver:
$ sudo xcode-select -s /Applications/Xcode.app/Contents/Developer
Why another node OCR package?
After doing a lot of research and trying to compile other node OCR packages for electron without success, I decided to create my own. Based on N-API, which would save me from a lot of trouble. Now it is used in Repeato, a low-code mobile app testing tool which works based on Computer Visions. Node-native-ocr enables Repeato to do text recognition and text assertions on Android and iOS and acrross all platforms such as React Native, Flutter or Unity.
Let me know about your projects too, and I can add them here to the list!
TSV format description
If you set the output option to 'tsv', you will get a table of data, cells separated by tabs. Since I had a hard time finding the format for it, I will paste it here: This is the original reference: https://www.tomrochette.com/tesseract-tsv-format
There are 12 columns in the table:
- level: hierarchical layout (a word is in a line, which is in a paragraph, which is in a block, which is in a page), a value from 1 to 5
- 1: page
- 2: block
- 3: paragraph
- 4: line
- 5: word
- page_num: when provided with a list of images, indicates the number of the file, when provided with a multi-pages document, indicates the page number, starting from 1
- block_num: block number within the page, starting from 0
- par_num: paragraph number within the block, starting from 0
- line_num: line number within the paragraph, starting from 0
- word_num: word number within the line, starting from 0
- left: x coordinate in pixels of the text bounding box top left corner, starting from the left of the image
- top: y coordinate in pixels of the text bounding box top left corner, starting from the top of the image
- width: width of the text bounding box in pixels
- height: height of the text bounding box in pixels
- conf: confidence value, from 0 (no confidence) to 100 (maximum confidence), -1 for all level except 5
- text: detected text, empty for all levels except 5
Development notes
To build the node-native-ocr project for testing, navigate into the node-native-ocr directory and exec
npm run install
I had problems with some node versions. A version which definitelly worked for me was v11.15.0.
After changing the code, and rebuilding the project, just run npm run test
License
MIT