QR Codes decoder with support of Numeric mode, Alphanumeric mode, Kanj mode, Byte mode and UTF8 mode.

The decoding rules of QRDecoders.jl follow the ISO/IEC 18004:2000 standard and are compatible with QRCoders.jl.

Decode a QR Code from a compact QR code matrix.

julia> # using Pkg; Pkg.add("QRCoders")
julia> using QRCoders, QRDecoders
julia> mat = qrcode("Hello World!"); # generate a QR code matrix
julia> info = qrdecode(mat)
QRInfo(1, Medium(), 0, UTF8(), "Hello World!")

The data type QRInfo contains information of the QR Code.

The result QRInfo(1, Medium(), 0, UTF8(), "Hello World!") means that the QR Code is of version 1, with medium error correction level, mask pattern 1, and is encoded by UTF8 mode with input message "Hello World!".

Decode a QR Code from an image without non-QRCode information:

julia> exportqrcode("Hello World!", "qrcode.png")
julia> qrdecode("qrcode.png")

Support for more complicate cases will be added in future work.

Decode message from an animated QR Code.

julia> exportqrcode(["hello", "julia"], "qrcode.gif")
julia> qrdecodes("qrcode.gif")

There are some options for the decoder that can be set by the keyword arguments.

First and foremost, we implement two algorithms for error correction:

• Berlekamp-Massey algorithm
• Sugiyama's adaption of Euclidean algorithm

The default algorithm is Euclidean algorithm, and one can specify the algorithm by the keyword argument alg. For example:

julia> qrdecode(mat; alg = BerlekampMassey())

The encoding mode Byte and UTF8 shared the same mode indicator 0100. Therefore, when dealing with cases about Byte mode or UTF8 mode, the decoder will try to decode the message with UTF8 mode first. If the decoding fails, then it will use the Byte mode. However, one can set the keyword preferutf8 to false to tell the decoder to skip the UTF8 check.

Examples:

julia> mat = qrcode("Hello world!");
julia> qrdecode(mat) # use UTF8 mode by defauls
QRInfo(1, Medium(), 5, UTF8(), "Hello world!")

julia> qrdecode(mat; preferutf8=false) # skip UTF8 check
QRInfo(1, Medium(), 5, Byte(), "Hello world!")

julia> mat = qrcode("©®"); # fail to use UTF8 mode
julia> qrdecode(mat)
QRInfo(1, Medium(), 5, Byte(), "©®")

Note: One should know that the UTF8 mode and Byte mode are the same for ascii characters. It only matters when the input message contains non-ascii characters.

Furthermore, there is one more option for the decoder, which is noerror. If noerror is set to be true, the QR matrix should be error-free. Otherwise, the decoder will raise DecodeError when it detects any error. This can be useful for tests of the Encode-Decode process interacting with QRCoders.jl.

The QRDecoders.jl is created as part of the OSPP'2022 project guided by Johnny Chen.