File Coverage

blib/lib/Photography/EV.pm

Criterion	Covered	Total	%
statement	53	63	84.1
branch	15	26	57.6
condition	3	3	100.0
subroutine	14	14	100.0
pod	3	3	100.0
total	88	109	80.7

package Photography::EV;

use strict;
use warnings;
use 5.020000;
use feature 'signatures';
no warnings 'experimental::signatures';
use base qw( Exporter );
BEGIN {
  eval q{
    use POSIX qw( pow );
  };
  if($@)
  {
    *pow = sub ($x, $exponent)
    {
      my $value = 1;
      for(1..$exponent)
      {
        $value *= $x;
      }
      $value;
    }
  }
}


our @EXPORT_OK = qw( ev aperture shutter_speed );
our @EXPORT = @EXPORT_OK;

# ABSTRACT: Calculate exposure value (EV)
our $VERSION = '0.05'; # VERSION


sub _round :prototype($)
{
  return $_[0] ? int($_[0] + $_[0]/abs($_[0]*2)) : 0;
}

sub _log2 :prototype($)
{
  return log($_[0])/log(2);
}

# returns the closest value in @$list to $exact
# returns undef if @$list is empty
sub _closest :prototype($$)
{
  my($exact, $list) = @_;
  my $answer;
  my $diff;
  for(@$list)
  {
    my $maybe = abs($_ - $exact);
    if((!defined $answer) || $maybe < $diff)
    {
      $answer = $_;
      $diff = $maybe;
    }
  }
  $answer;
}

my @apertures = qw(
  1.0
  1.4
  2.8
  4.0
  5.6
  8.0
  11
  16
  22
  32
  45
  64
);

my @times = (
  (map { $_ * 60 } qw( 32 16 8 4 2 )),
  (                qw( 60 30 15 8 4 2 1)),
  (map { 1 / $_  } qw( 2 4 8 15 30 125 250 500 1000 2000 4000 8000 ))
);


sub ev ($aperture, $time)
{
  return _round _log2 $aperture*$aperture/$time;
}


sub aperture ($ev, $time, $apertures = \@apertures )
{
  return _closest sqrt pow(2, $ev)*$time, $apertures;
}


sub shutter_speed ($ev, $aperture, $times = \@times )
{
  return _closest $aperture*$aperture/pow(2, $ev), $times;
}

1;

__END__