NAME
puzzle_set_max_width, puzzle_set_max_height, puzzle_set_lambdas,
puzzle_set_p_ratio, puzzle_set_noise_cutoff,
puzzle_set_contrast_barrier_for_cropping,
puzzle_set_max_cropping_ratio, puzzle_set_autocrop - set tunables for
libpuzzle functions
SYNOPSIS
#include <puzzle.h>
int puzzle_set_max_width(PuzzleContext *context, unsigned int width);
int puzzle_set_max_height(PuzzleContext *context, unsigned int height);
int puzzle_set_lambdas(PuzzleContext *context, unsigned int lambdas);
int puzzle_set_p_ratio(PuzzleContext *context, double p_ratio);
int puzzle_set_noise_cutoff(PuzzleContext *context, double
noise_cutoff);
int puzzle_set_contrast_barrier_for_cropping(PuzzleContext *context,
double barrier);
int puzzle_set_max_cropping_ratio(PuzzleContext *context, double
ratio);
int puzzle_set_autocrop(PuzzleContext *context, int enable);
DESCRIPTION
While default values have been chosen to be ok for most people, the
puzzle_set_*() functions are knobs to fit the algorithm to your set of
data and to your applications.
LAMBDAS
By default, pictures are divided in 9 x 9 blocks.
9 is the lambdas value, and it can be changed with
puzzle_set_lambdas().
For large databases, for complex images, for images with a lot of text
or for sets of near-similar images, it might be better to raise that
value to 11 or even 13.
However, raising that value obviously means that vectors will require
more storage space.
The lambdas value should remain the same in order to get comparable
vectors. So if you pick 11 (for instance), you should always use that
value for all pictures you will compute a digest for
puzzle_set_p_ratio().
The average intensity of each block is based upon a small centered
zone.
The "p ratio" determines the size of that zone. The default is 2.0, and
that ratio mimics the behavior that is described in the reference
algorithm.
For very specific cases (complex images) or if you get too many false
positives, as an alternative to increasing lambdas, you can try to
lower that value, for instance to 1.5.
The lowest acceptable value is 1.0.
MAXIMUM SIZES
In order to avoid CPU starvation, pictures won’t be processed if their
width or height is larger than 3000 pixels.
These limits are rather large, but if you ever need to change them, the
puzzle_set_max_width() and puzzle_set_max_height() are available.
NOISE CUTOFF
The noise cutoff defaults to 2. If you raise that value, more zones
with little difference of intensity will be considered as similar.
Unless you have very specialized sets of pictures, you probably don’t
want to change this.
AUTOCROP
By default, featureless borders of the original image are ignored. The
size of each border depends on the sum of absolute values of
differences between adjacent pixels, relative to the total sum.
That feature can be disabled with puzzle_set_autocrop(0), any other
value will enable it.
puzzle_set_contrast_barrier_for_cropping() changes the tolerance. The
default value is 5. Less shaves less, more shaves more.
puzzle_set_max_cropping_ratio() : this is a safe-guard against unwanted
excessive auto-cropping.
The default (0.25) means that no more than 25% of the total width (or
height) will ever be shaved.
RETURN VALUE
Functions return 0 on success, and -1 if something went wrong.
AUTHORS
Frank DENIS libpuzzle at pureftpd dot org
SEE ALSO
libpuzzle(3), puzzle-diff(8)
2010-06-09 debian::manpages::puzzle_set(3)