NAME

       puzzle_init_cvec, puzzle_init_dvec, puzzle_fill_dvec_from_file,
       puzzle_fill_cvec_from_file, puzzle_fill_cvec_from_dvec, puzzle_free_cvec,
       puzzle_free_dvec, puzzle_init_compressed_cvec, puzzle_free_compressed_cvec,
       puzzle_compress_cvec, puzzle_uncompress_cvec, puzzle_vector_normalized_distance - compute
       comparable signatures of bitmap images

SYNOPSIS

       #include <puzzle.h>

       int puzzle_init_context(PuzzleContext *context);

       int puzzle_free_context(PuzzleContext *context);

       int puzzle_init_cvec(PuzzleContext *context, PuzzleCvec *cvec);

       int  puzzle_init_dvec(PuzzleContext *context, PuzzleDvec *cvec);

       void puzzle_fill_dvec_from_file(PuzzleContext *context, PuzzleDvec *dvec, const char
       *file);

       void puzzle_fill_cvec_from_file(PuzzleContext *context, PuzzleCvec *cvec, const char
       *file);

       void puzzle_fill_cvec_from_dvec(PuzzleContext *context, PuzzleCvec *cvec, const PuzzleDvec
       *dvec);

       void puzzle_free_cvec(PuzzleContext *context, PuzzleCvec *cvec);

       void puzzle_free_dvec(PuzzleContext *context, PuzzleDvec *cvec);

       void puzzle_init_compressed_cvec(PuzzleContext *context, PuzzleCompressedCvec
       *compressed_cvec);

       void puzzle_free_compressed_cvec(PuzzleContext *context, PuzzleCompressedCvec
       *compressed_cvec);

       int puzzle_compress_cvec(PuzzleContext *context, PuzzleCompressedCvec *compressed_cvec,
       const PuzzleCvec *cvec);

       int puzzle_uncompress_cvec(PuzzleContext *context, PuzzleCompressedCvec *compressed_cvec,
       PuzzleCvec *const cvec);

       double puzzle_vector_normalized_distance(PuzzleContext *context, const PuzzleCvec *cvec1,
       const PuzzleCvec *cvec2, const int fix_for_texts);

DESCRIPTION

       The Puzzle library computes a signature out of a bitmap picture. Signatures are comparable
       and similar pictures have similar signatures.

       After a picture has been loaded and uncompressed, featureless parts of the image are
       skipped (autocrop), unless that step has been explicitly disabled, see puzzle_set(3)

LIBPUZZLE CONTEXT

       Every public function requires a PuzzleContext object, that stores every required
       tunables.

       Any application using libpuzzle should initialize a PuzzleContext object with
       puzzle_init_context() and free it after use with puzzle_free_context()

         PuzzleContext context;

         puzzle_init_context(&context);
         [...]
         puzzle_free_context(&context);

DVEC AND CVEC VECTORS

       The next step is to divide the cropped image into a grid and to compute the average
       intensity of soft-edged pixels in every block. The result is a PuzzleDvec object.

       PuzzleDvec objects should be initialized before use, with puzzle_init_dvec() and freed
       after use with puzzle_free_dvec().

       The PuzzleDvec structure has two important fields: vec is the pointer to the first element
       of the array containing the average intensities, and sizeof_compressed_vec is the number
       of elements.

       PuzzleDvec objects are not comparable, so what you usually want is to transform these
       objects into PuzzleCvec objects.

       A PuzzleCvec object is a vector with relationships between adjacent blocks from a
       PuzzleDvec object.

       The puzzle_fill_cvec_from_dvec() fills a PuzzleCvec object from a PuzzleDvec object.

       But just like the other structure, PuzzleCvec objects must be initialized and freed with
       puzzle_init_cvec() and puzzle_free_cvec().

       PuzzleCvec objects have a vector whoose first element is in the vec field, and the number
       of elements is in the sizeof_vec field.

LOADING PICTURES

       PuzzleDvec and PuzzleCvec objects can be computed from a bitmap picture file, with
       puzzle_fill_dvec_from_file() and puzzle_fill_cvec_from_file().

       GIF, PNG and JPEG files formats are currently supported and automatically recognized.

       Here's a simple example that creates a PuzzleCvec objects out of a file.

         PuzzleContext context;
         PuzzleCvec cvec;

         puzzle_init_context(&context);
         puzzle_init_cvec(&context, &cvec);
         puzzle_fill_cvec_from_file(&context, &cvec, "test-picture.jpg");
         [...]
         puzzle_free_cvec(&context, &cvec);
         puzzle_free_context(&context);

COMPARING VECTORS

       In order to check whether two pictures are similar, you need to compare their PuzzleCvec
       signatures, using puzzle_vector_normalized_distance().

       That function returns a distance, between 0.0 and 1.0. The lesser, the nearer.

       Tests on common pictures show that a normalized distance of 0.6 (also defined as
       PUZZLE_CVEC_SIMILARITY_THRESHOLD) means that both pictures are visually similar.

       If that threshold is not right for your set of pictures, you can experiment with
       PUZZLE_CVEC_SIMILARITY_HIGH_THRESHOLD, PUZZLE_CVEC_SIMILARITY_LOW_THRESHOLD and
       PUZZLE_CVEC_SIMILARITY_LOWER_THRESHOLD or with your own value.

       If the fix_for_texts of puzzle_vector_normalized_distance() is 1, a fix is applied to the
       computation in order to deal with bitmap pictures that contain text. That fix is
       recommended, as it allows using the same threshold for that kind of picture as for generic
       pictures.

       If fix_for_texts is 0, that special way of computing the normalized distance is disabled.

         PuzzleContext context;
         PuzzleCvec cvec1, cvec2;
         double d;

         puzzle_init_context(&context);
         puzzle_init_cvec(&context, &cvec1);
         puzzle_init_cvec(&context, &cvec2);
         puzzle_fill_cvec_from_file(&context, &cvec1, "test-picture-1.jpg");
         puzzle_fill_cvec_from_file(&context, &cvec2, "test-picture-2.jpg");
         d = puzzle_vector_normalized_distance(&context, &cvec1, &cvec2, 1);
         if (d < PUZZLE_CVEC_SIMILARITY_THRESHOLD) {
           puts("Pictures are similar");
         }
         puzzle_free_cvec(&context, &cvec2);
         puzzle_free_cvec(&context, &cvec1);
         puzzle_free_context(&context);

CVEC COMPRESSION

       In order to reduce storage needs, PuzzleCvec objects can be compressed to 1/3 of their
       original size.

       PuzzleCompressedCvec structures hold the compressed data. Before and after use, these
       structures have to be passed to puzzle_init_compressed_cvec() and
       puzzle_free_compressed_cvec().

       puzzle_compress_cvec() compresses a PuzzleCvec object into a PuzzleCompressedCvec object.

       And puzzle_uncompress_cvec() uncompresses a PuzzleCompressedCvec object into a PuzzleCvec
       object.

         PuzzleContext context;
         PuzzleCvec cvec;
         PuzzleCompressedCvec c_cvec;
         [...]
         puzzle_init_compressed_cvec(&context, &c_cvec);
         puzzle_compress_cvec(&context, &c_cvec, &cvec);
         [...]
         puzzle_free_compressed_cvec(&context, &c_cvec);

       The PuzzleCompressedCvec structure has two important fields: vec that is a pointer to the
       first element of the compressed data, and sizeof_compressed_vec that contains the number
       of elements.

RETURN VALUE

       Functions return 0 on success, and -1 if something went wrong.

AUTHORS

       Frank DENIS libpuzzle at pureftpd dot org

ACKNOWLEDGMENTS

       Xerox Research Center H. CHI WONG Marschall BERN David GOLDBERG Sameh SCHAFIK

SEE ALSO

       puzzle_set(3), puzzle-diff(8)

                                            2016-04-05             debian::manpages::libpuzzle(3)