/ 
Image-DecodeQR-WeChat-0.10
/ README.md

NAME

Image::DecodeQR::WeChat - Decode QR code(s) from images using the OpenCV/WeChat library via XS

VERSION

Version 0.10

SYNOPSIS

This module provides a Perl interface to the OpenCV/WeChat QR code decoder via XS code. OpenCV/WeChat library uses CNN (Convolutional Neural Networks) to do this with pre-trained models.

This module has been tested by myself with OpenCV v4.5.5, v4.8.1 and Perl v5.32, v5.38 on Linux. But check the CPANtesters matrix on the left for all the tests done on this module (although tests may be sparse and rare because of the OpenCV dependency).

The library is relatively successful even for rotated codes. It remains to be tested on the minimum size of the code images (60px in my case). In producing test images with software like the GIMP, one should be aware of the distortions caused by transforms such as scale and rotation to the final QR code images, rotation in particular. Add certain enhancements to the final image to "look good" and the resultant image looks like QR code but it is not. Failure of the library on such artificially produced images would be somehow expected. Instead I would test with images which have been scanned with a QR code image attached to them in random angles. This is my use case afterall: scanned images with a glued-in QR code tag so that my systems would archive it straight from the scanner into the right database table.

Here is some code to get you started:

# this ensures that both input params can contain utf8 strings
# but also results (somehow but beyond me)
use Image::DecodeQR::WeChat;

# this will be fixed, right now params are hardoded in XS code
my $ret = Image::DecodeQR::WeChat::decode_xs(
    # the input image containing one or more QR-codes
    'an-input-image.png',

    # the dir with model parameters required by the library.
    # Model files come with this Perl module and are curtesy of WeChat
    # which is part of OpenCV contrib packages.
    # They are installed with this module and their default location
    # is given by Image::DecodeQR::WeChat::modelsdir()
    # Alternatively, you specify here your own model files:
    Image::DecodeQR::WeChat::modelsdir(),

    # outbase for all output files, optional
    # if more than one QR-codes were detected then an index will
    # be appended to the filename. And there will be png image files
    # containing the portion of the image which was detected
    # and there will be txt files with QR-code text (payload)
    # and its bounding box. And there will be an overall
    # text file with all payloads. This last one will be
    # printed to STDOUT if no outbase was specified:
    'output.detected',

    # verbosity level. 0:mute, 1:C code messages, 10:C+XS code
    10,

    # display results in a window with QR codes found highlighted
    # make sure you have an interactive shell and GUI
    1,

    # dump image and metadata to files for each QR code detected
    # only if outbase was specified
    1,
);
die "failed" unless $ret;
# we got back an array-of-2-arrays
# * one contains the QR-code-text (called payload)
# * one contains bounding boxes, one for each payload
# we have as many payloads and bounding boxes as
# are the QR-codes detected (some may have been skipped)

my ($payloads, $boundingboxes) = @$ret;
for (0..$#$payloads){
  print "Payload got: '".$payloads->[$_]
    ."' bbox: @{$boundingboxes->[$_]}"
    .".\n";
}

# The above decode_xs() expects all parameters to be present
# while decode() below takes a hash of params and fills the
# missing params with defaults. Then it calls decode_xs()
# So, it is still calling XS code but via a Perl sub
# The important bit is that the modelsdir is filled in automatically
# rather than the user looking for it
my $ret = Image::DecodeQR::WeChat::decode({
    # these are required
    'input' => 'input.jpg',
    'outbase' => 'outs',
    # these are optional and have defaults
    #'modelsdir' => '...', # use it only if you have your own models
    #'verbosity' => 0,
    #'graphicaldisplayresult'' => 0,
    #'dumpqrimagestofile' => 0,
});
die "failed" unless $ret;
my ($payloads, $boundingboxes) = @$ret;
for (0..$#$payloads){
  print "Payload got: '".$payloads->[$_]
    ."' bbox: @{$boundingboxes->[$_]}"
    .".\n";
}

# pre-trained models location (installed with this module)
print "my models are in here: ".Image::DecodeQR::WeChat::modelsdir()."\n"

# returns 1 or 0 when OpenCV was compiled with highgui or not
# and supports GUI display like imshow() which displays an image in a window
my $has_highgui_support = opencv_has_highgui_xs();

This code calls functions and methods from OpenCV/WeChat library (written in C++) for decoding one or more QR codes found embedded in images. It's just that: a very thin wrapper of a C++ library written in XS. It only interfaces the OpenCV/WeChat library for QR code decoding.

It can detect multiple QR codes embeded in a single image. And has been successfully tested with as small sizes as 60 x 60 px.

The payload(s) (the QR-code's text) are returned back as an ARRAYref.

Optionally, it can output the portion of the input image corresponding to each QR-code, its bounding box and the payload in separate files, useful for debugging and identification when multiple QR codes exist in a single input image.

Following this code as an example, it will be trivial to interface other parts of the OpenCV library:

Ιδού πεδίον δόξης λαμπρόν
   (behold a glorious field of glory)

EXPORT

COMMAND LINE SCRIPT

image-decodeqr-wechat.pl --input image-with-qr-code.jpg

image-decodeqr-wechat.pl --help

A CLI script is provided and will be installed by this module. Basic usage is as above. Here is its usage:

Usage : script/image-decodeqr-wechat.pl <options>

where options are:

  --input F :
    the filename of the input image
    which supposedly contains QR codes to be detected.

  --modelsdir M :
    optionally use your own models contained
    in this directory instead of the ones
    this program was shipped with.

  --outbase O :
    basename for all output files
    (if any, depending on whether --dumpqrimagestofile is on).

  --verbosity L :
    verbosity level, 0:mute, 1:C code, 10:C+XS code.

  --graphicaldisplayresult :
    display a graphical window with input image
    and QR codes outlined. Using --dumpqrimagestofile
    and specifying --outbase, images and payloads and
    bounding boxes will be saved to files, if you do
    not have graphical interface.

  --dumpqrimagestofile :
    it has effect only of --outbase was specified. Payloads,
    Bounding Boxes and images of each QR-code detected will
    be saved in separate files.

PREREQUISITES

SUBROUTINES/METHODS

decode_xs(infile, modelsdir, outbase, verbosity, graphicaldisplayresult, dumpqrimagestofile)

It takes in the filename of an input image which may contain one or more QR codes and returns back an ARRAYref of strings containing all the payloads of the codes which have successfully been decoded (some QR codes may fail to be decoded because of resolution or quality etc.)

It returns undef on failure.

It returns an empty ARRAYref (i.e. a ref to an empty array) if no QR codes were found or decoded successfully.

These are the parameters it requires. They must all be present, with optional parameters allowed to be undef:

decode(\%params)

This is a Perl wrapper to the decode_xs() and allows a user to specify only a minimal set of parameters with the rest to be filled in by defaults.

Like decode_xs(), it returns undef on failure. Or an arrayref of two arrays. The payloads array and the bounding-boxes array. Each has a number of items equal to the QR codes detected.

An ARRAYref of two empty arrays will be returned if no QR codes were found or decoded successfully.

The params hashref:

modelsdir()

It returns the path where the models included in this Perl module have been installed. This is useful when you want to use decode_xs() and need to specify the modelsdir. Just pass the output of this to decode_xs() as its modelsdir parameter. However, you can not set the location of your own modelsdir using modelsdir().

opencv_has_highgui_xs()

It returns 1 or 0 depending on whether current OpenCV installation has support for graphical display of images (the imshow() function). This affects the option graphicaldisplayresult to decode() and decode_xs() which will be ignored if there is no highgui support.

Caveat: checking for whether current OpenCV installation has highgui support is currently very lame, it merely tries to find the include file opencv2/highgui.hpp in the Include dirs. I have tried several methods (see ```Makefile.PL```), for example DynaLoader or FFI::CheckLib can search for symbols in any library (e.g. searching for imshow() in libopencv_highgui or libopencv_world). This would have been the most straight-forward way but alas, these are C++ libraries and function names are mangled to weird function names like:

ZN2cv3viz6imshowERKNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEEERKNS_11_InputArrayERKNS_5Size_IiEE()

There's an imshow() in there but without a regex symbol-name search the symbol can not be detected.

Another take is with Devel::CheckLib which supports compiling code snippets when searching for a particular library. This fails because they ... allow only a C compiler but we need a C++ compiler.

Finally, using Inline::CPP to compile our own snippet is totally in vain because of its useless form of running as use Inline CPP = ... >. I could not find any way of telling it to use specific CFLAGS and LDFLAGS with this useless use Inline CPP form.

IMPLEMENTATION DETAILS

This code demonstrates how to call OpenCV (modern OpenCV v4) C++ methods using the technique suggested by Botje @ #perl in order to avoid all the function, macro, data structures name clashes between Perl and OpenCV (for example seed(), do_open(), do_close() and most notably struct cv and namespace cv in Perl and OpenCV respectively).

The trick suggested is to put all the OpenCV-calling code in a separate C++ file and provide high-level functions to be called by XS. So that the XS code does not see any OpenCV header files.

Makefile.PL will happily compile any .c and/or .cpp files found in the dir it resides by placing OBJECT => '$(O_FILES)' in %WriteMakefileArgs. And will have no problems with specifying also these:

CC      => 'g++',
LD      => 'g++',
XSOPT   => '-C++',

With one caveat, g++ compiler will mangle the names of the functions when placing them in the object files. And that will cause XSLoader to report missing and undefined symbols.

The cure to this is to wrap any function you want to remain unmangled within

#ifdef __cplusplus
extern "C" {
#endif

and

#ifdef __cplusplus
} //extern "C" {
#endif

This only need happen in the header file: wechat_qr_decode_lib.hpp and in the XS file where the Perl headers are included.

INSTALLING OpenCV

In my case installing OpenCV using Linux's package manager (dnf, fedora) was not successful with default repositories. It required to add another repository (rpmfusion) which wanted to install its own versions of packages I already had. So I prefered to install OpenCV from sources. This is the procedure I followed:

Your mileage may vary.

If you are seriously in need of installing this module then consider migrating to a serious operating system such as Linux as your first action.

INSTALLING THIS MODULE

This module depends on the existence of the OpenCV library with all the extensions and contributed modules mentioned in section PREREQUISITES.

Detecting where this library is located in your system is the weakest link in the installation process of this module. Makefile.PL contains code to do this with pkg-config or cmake. If these fail, it will look for ENVironment variables: OPENCV_LDFLAGS and OPENCV_CFLAGS, which should contain the CFLAGS (for example: <-I/usr/include/opencv4/>) and LDFLAGS (for example: <-L/usr/lib64 -lopencv_world>). Set these variables manually prior installation if the automatic methods mentioned above fail.

One last thing to check is that if your OpenCV installation (developer version) was correct, there should be a pkg-config file, perhaps in /usr/lib64/pkgconfig/opencv4.pc or /usr/local/lib64/pkgconfig/opencv4.pc. This file details all the CFLAGS and LDFLAGS and should be found by Makefile.PL if it is in a standard location, or adjust the list of paths in environment variable PKG_CONFIG_PATH which is where pkg-config searches for these files.

AUTHOR

Andreas Hadjiprocopis, <bliako at cpan.org>

BUGS

Please report any bugs or feature requests to bug-image-decodeqr-wechat at rt.cpan.org, or through the web interface at https://rt.cpan.org/NoAuth/ReportBug.html?Queue=Image-DecodeQR-WeChat. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

SUPPORT

You can find documentation for this module with the perldoc command.

perldoc Image::DecodeQR::WeChat

You can also look for information at:

ACKNOWLEDGEMENTS

LICENSE AND COPYRIGHT

This software is Copyright (c) 2022 by Andreas Hadjiprocopis.

This is free software, licensed under:

The Artistic License 2.0 (GPL Compatible)

HUGS

!Almaz!