src/third_party/quirc/README - cobalt - Git at Google

 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.
	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.