jsQR

A pure javascript port of the ZXing QR parsing library. This library takes in raw images and will locate, extract and parse any QR codes found within. It also exposes methods to do each step of the process individually. This allows piecemeal use and custom extension, for example you can use this library to parse pure QR codes (without extracting from an image), or to locate QR codes within an image without parsing them.

See a demo

Motivation

This library was written because there were no javascript QR code parsing libraries that were well maintained and capable of parsing any reasonably complex QR codes.

See how jsQR compares to other JS QR code decoders

ZXing is the best QR code library, and had been ported to many languages, but not to Javascript. jsQR is a fully featured port of the QR code portions of the zxing library, with the goal of growing into a maintainable and extendable QR parsing library in pure javascript.

Documentation

Installation

NodeJS

npm install jsqr --save

jsQR = require("jsqr");

Browser

Include jsQR.js.

<script src="jsQR.js"></script>

You can also use module loaders such as requireJS or browserify

Usage

qrJS exports methods for each step in the QR recognition, extraction and decoding process, as well as a convenience wrapper method.

Examples

Using the wrapper method

var decoded = jsQR.decodeQRFromImage(data, width, height);

Using the individual methods

var binarizedImage = binarizeImage(data, width, height);
var location = locateQRInBinaryImage(binarizedImage);
if (!location) {
  return;
}
var rawQR = extractQRFromBinaryImage(binarizedImage, location);
if (!rawQR) {
  return;
}

console.log(decodeQR(rawQR));

Working example of parsing a webcam feed

Methods

qrJS.decodeQRFromImage(data, width, height)

decodeQRFromImage is a wrapper method for the different steps of the QR decoding process. It takes in a RGBA image and returns a string representation of the data encoded within any detected QR codes.

Arguments

• data - An 1d array of numbers representing an RGBA image in the form r1, g1, b1, a1, r2, g2, b2, a2,.... This is the same form as the ImageData type returned by the .getImageData() call when reading data from a canvas element.
• width - The width of the image.
• height The height of the image.

data.length should always be equal to width * height * 4.

qrJS.binarizeImage(data, width, height)

Binarizing an image (converting it to an image where pixels are either back or white, not grey) is the first step of the process. binarizeImage takes in a RGBA image and returns a BitMatrix representing the binarized form of that image.

Arguments

• data - An 1d array of numbers representing an RGBA image in the form r1, g1, b1, a1, r2, g2, b2, a2,.... This is the same form as the ImageData type returned by the .getImageData() call when reading data from a canvas element.
• width - The width of the image.
• height The height of the image.

data.length should always be equal to width * height * 4.

qrJS.locateQRInBinaryImage(image)

locateQRInBinaryImage takes in a BitMatrix representing a binary image (as output by binarizeImage) and returns the location of a QR code if one is detected.

Arguments

• image - a BitMatrix representing a binary image (as output by binarizeImage)

Returns

locateQRInBinaryImage returns null if no QR is found, else it returns an object with the following structure

{
  bottomLeft: {
    x: number,
    y: number
  },
  topLeft: {
    x: number,
    y: number
  },
  topRight: {
    x: number,
    y: number
  }
}

The coordinates represent the pixel locations of the QR's corner points.

qrJS.extractQRFromBinaryImage(image, location)

extractQRFromBinaryImage takes in a BitMatrix representing a binary image (as output by binarizeImage) and the location of a QR code. It returns a BitMatrix representing the raw QR code.

Arguments

• image - a BitMatrix representing a binary image (as output by binarizeImage)
• location - The location of a QR code, as returned by locateQRInBinaryImage

Returns

extractQRFromBinaryImage a BitMatrix representing the extracted QR code. The matrix is size N by N where N is the number of "blocks" along the edge of the QR code.

qrJS.decodeQR(qrCode)

decodeQR takes in a BitMatrix representing a raw QR code (as output by extractQRFromBinaryImage) and returns a string of decoded data. It is the last step in the QR decoding process.

Arguments

• qrCode - a BitMatrix representing a raw QR code (as output by extractQRFromBinaryImage)

BitMatrices

Throughout the QR extraction and decoding process data is often represented as a BitMatrix. BitMatrices are a convenient way to represent and interact with a 2d array of booleans.

Properties

• width - The width of the matrix.
• height - The height of the matrix.
• data - The underlying data (represented as a 1d array)

Methods

• get(x, y) - Get the bit at specific coordinates.
• set(x, y, bit) - Set the bit at specific coordinates.

qrJS.createBitMatrix(data, width)

createBitMatrix is a convenience method for creating bit matrices.

Arguments

• data - A 1d array of booleans representing the data represented by the bit matrix.
• width - The width of the matrix (height is inferred by data.length / width).

State of the library

jsQR was originally written by porting over the ZXing C# library directly to typescript. This lead to code that works extremely well, but may not follow best javascript practices.

The next steps (which are ongoing) are to port over any test cases (writing any that don't exist), and refactor each of the modules into more idomatic code. The end goal is a pure JS library QR library that is as fully featured as the ZXing library, but maintainable and extendable in it's own right.

Contributing

jsQR is written using typescript. You can view the development source in the src directory.

Currently the library is very untested, but tests are being added as the library is refactored into more maintainable code. Tests can be run via

npm test

After testing any changes, you can compile the production version by running

npm run-script build

• Source hosted at GitHub
• Report issues, questions, feature requests on GitHub Issues

Pull requests are welcome! Please create seperate branches for seperate features/patches.