Provided by: libpuzzle-dev_0.11-2_amd64 
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) debian::manpages::libpuzzle(3)