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QR decoder library

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README
Quirc
=====

QR codes are a type of high-density matrix barcodes, and quirc is a
library for extracting and decoding them from images. It has several
features which make it a good choice for this purpose:

  * It is fast enough to be used with realtime video: extracting and
    decoding from VGA frame takes about 50 ms on a modern x86 core.

  * It has a robust and tolerant recognition algorithm. It can
    correctly recognise and decode QR codes which are rotated and/or
    oblique to the camera. It can also distinguish and decode multiple
    codes within the same image.

  * It is easy to use, with a simple API described in a single
    commented header file (see below for an overview).

  * It is small and easily embeddable, with no dependencies other than
    standard C functions.

  * It has a very small memory footprint: one byte per image pixel,
    plus a few kB per decoder object.

  * It uses no global mutable state, and is safe to use in a
    multithreaded application.

  * BSD-licensed, with almost no restrictions regarding use and/or
    modification.

The distribution comes with, in addition to the library, several test
programs. While the core library is very portable, these programs have
some additional dependencies. All of them require libjpeg, and two
(``quirc-demo`` and ``inspect``) require SDL. The camera demos use
Linux-specific APIs:

``quirc-demo``

  ~ This is an real-time demo which requires a camera and a graphical
    display. The video stream is displayed on screen as it's received,
    and any QR codes recognised are highlighted in the image, with the
    decoded information both displayed on the image and printed on
    stdout.

``quirc-scanner``

  ~ This program turns your camera into a barcode scanner. It's almost
    the same as the ``demo`` application, but it doesn't display the
    video stream, and thus doesn't require a graphical display.

``qrtest``

  ~ This test is used to evaluate the performance of library. Given a
    directory tree containing a bunch of JPEG images, it will attempt
    to locate and decode QR codes in each image. Speed and success
    statistics are collected and printed on stdout.

``inspect``

  ~ This test is used for debugging. Given a single JPEG image, it
    will display a diagram showing the internal state of the decoder
    as well as printing additional information on stdout.

Installation
------------

To build the library and associated demos/tests, type ``make``. Type
``make install`` to install the library, header file and camera demos.

You can specify one or several of the following targets if you don't
want, or are unable to build everything:

  * libquirc.a
  * libquirc.so
  * qrtest
  * inspect
  * quirc-scanner
  * quirc-demo

Library use
-----------

All of the library's functionality is exposed through a single header
file, which you should include:

    #include <quirc.h>

To decode images, you'll need to instantiate a ``struct quirc``
object, which is done with the ``quirc_new`` function. Later, when you
no longer need to decode anything, you should release the allocated
memory with ``quirc_destroy``:

    struct quirc *qr;

    qr = quirc_new();
    if (!qr) {
	    perror("Failed to allocate memory");
	    abort();
    }

    /* ... */

    quirc_destroy(qr);

Having obtained a decoder object, you need to set the image size that
you'll be working with, which is done using ``quirc_resize``:

    if (quirc_resize(qr, 640, 480) < 0) {
	    perror("Failed to allocate video memory");
	    abort();
    }

``quirc_resize`` and ``quirc_new`` are the only library functions
which allocate memory. If you plan to process a series of frames (or a
video stream), you probably want to allocate and size a single decoder
and hold onto it to process each frame.

Processing frames is done in two stages. The first stage is an
image-recognition stage called identification, which takes a grayscale
image and searches for QR codes. Using ``quirc_begin`` and
``quirc_end``, you can feed a grayscale image directly into the buffer
that ``quirc`` uses for image processing:

    uint8_t *image;
    int w, h;

    image = quirc_begin(qr, &w, &h);

    /* Fill out the image buffer here.
     * image is a pointer to a w*h bytes.
     * One byte per pixel, w pixels per line, h lines in the buffer.
     */

    quirc_end(qr);

Note that ``quirc_begin`` simply returns a pointer to a previously
allocated buffer. The buffer will contain uninitialized data. After
the call to ``quirc_end``, the decoder holds a list of detected QR
codes which can be queried via ``quirc_count`` and ``quirc_extract``.

At this point, the second stage of processing occurs -- decoding. This
is done via the call to ``quirc_decode``, which is not associated with
a decoder object.

    int num_codes;
    int i;

    /* We've previously fed an image to the decoder via
     * quirc_begin/quirc_end.
     */

    num_codes = quirc_count(qr);
    for (i = 0; i < num_codes; i++) {
	    struct quirc_code code;
	    struct quirc_data data;
	    quirc_decode_error_t err;

	    quirc_extract(qr, i, &code);

	    /* Decoding stage */
	    err = quirc_decode(&code, &data);
	    if (err)
		    printf("DECODE FAILED: %s\n", quirc_strerror(err));
	    else
		    printf("Data: %s\n", data.payload);
    }

``quirc_code`` and ``quirc_data`` are flat structures which don't need
to be initialized or freed after use.

Copyright
---------

Copyright (C) 2010-2012 Daniel Beer <<dlbeer@gmail.com>>

Permission to use, copy, modify, and/or distribute this software for
any purpose with or without fee is hereby granted, provided that the
above copyright notice and this permission notice appear in all
copies.

THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
PERFORMANCE OF THIS SOFTWARE.
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