File Coverage

blib/lib/Convert/Color/HSV.pm

Criterion	Covered	Total	%
statement	55	60	91.6
branch	15	24	62.5
condition			n/a
subroutine	14	14	100.0
pod	9	10	90.0
total	93	108	86.1

#  You may distribute under the terms of either the GNU General Public License
#  or the Artistic License (the same terms as Perl itself)
#
#  (C) Paul Evans, 2009-2022 -- [e-mail]

package Convert::Color::HSV 0.17;

use v5.14;
use warnings;
use base qw( Convert::Color::HueChromaBased );

__PACKAGE__->register_color_space( 'hsv' );

use Carp;

=head1 NAME

C - a color value represented as hue/saturation/value

=head1 SYNOPSIS

Directly:

   use Convert::Color::HSV;

   my $red = Convert::Color::HSV->new( 0, 1, 1 );

   # Can also parse strings
   my $pink = Convert::Color::HSV->new( '0,0.7,1' );

Via L:

   use Convert::Color;

   my $cyan = Convert::Color->new( 'hsv:300,1,1' );

=head1 DESCRIPTION

Objects in this class represent a color in HSV space, as a set of three
floating-point values. Hue is stored as a value in degrees, in the range
0 to 360 (exclusive). Saturation and value are in the range 0 to 1.

This color space may be considered as a cylinder, of height and radius 1. Hue
represents the position of the color as the angle around the axis, the
saturation the distance from the axis, and the value the height above the
base. In this shape, the entire base of the cylinder is pure black, the axis
through the centre represents the range of greys, and the circumference of the
top of the cylinder contains the pure-saturated color wheel, with a pure
white point at its centre.

Because the entire bottom surface of this cylinder contains black, a
closely-related color space can be created by reshaping the cylinder into a
cone by contracting the base of the cylinder into a point. The radius from the
axis is called the chroma (though this is a different definition of "chroma"
than that used by CIE).

=cut

=head1 CONSTRUCTOR

=cut

=head2 new

   $color = Convert::Color::HSV->new( $hue, $saturation, $value )

Returns a new object to represent the set of values given. The hue should be
in the range 0 to 360 (exclusive), and saturation and value should be between
0 and 1. Values outside of these ranges will be clamped.

   $color = Convert::Color::HSV->new( $string )

Parses C<$string> for values, and construct a new object similar to the above
three-argument form. The string should be in the form

   hue,saturation,value

containing the three floating-point values in decimal notation.

=cut

sub new
{
   my $class = shift;

   my ( $h, $s, $v );

   if( @_ == 1 ) {
      local $_ = $_[0];
      if( m/^(\d+(?:\.\d+)?),(\d+(?:\.\d+)?),(\d+(?:\.\d+)?)$/ ) {
         ( $h, $s, $v ) = ( $1, $2, $3 );
      }
      else {
         croak "Unrecognised HSV string spec '$_'";
      }
   }
   elsif( @_ == 3 ) {
      ( $h, $s, $v ) = @_;
   }
   else {
      croak "usage: Convert::Color::HSV->new( SPEC ) or ->new( H, S, V )";
   }

   # Clamp
   for ( $s, $v ) {
      $_ = 0 if $_ < 0;
      $_ = 1 if $_ > 1;
   }

   # Fit to range [0,360)
   $h += 360 while $h < 0;
   $h -= 360 while $h >= 360;

   return bless [ $h, $s, $v ], $class;
}

=head1 METHODS

=cut

=head2 hue

   $h = $color->hue

=head2 saturation

   $s = $color->saturation

=head2 value

   $v = $color->value

Accessors for the three components of the color.

=cut

# Simple accessors
sub hue        { shift->[0] }
sub saturation { shift->[1] }
sub value      { shift->[2] }

=head2 chroma

   $c = $color->chroma

Returns the derived property of "chroma", which maps the color space onto a
cone instead of a cylinder. This more closely measures the intuitive concept
of how "colorful" the color is than the saturation value and is useful for
distance calculations.

=cut

sub chroma
{
   my $self = shift;
   return $self->saturation * $self->value;
}

=head2 hsv

   ( $hue, $saturation, $value ) = $color->hsv

Returns the individual hue, saturation and value components of the color
value.

=cut

sub hsv
{
   my $self = shift;
   return @$self;
}

# Conversions
sub rgb
{
   my $self = shift;

   # See also
   #  http://en.wikipedia.org/wiki/HSV_color_space

   my ( $h, $s, $v ) = $self->hsv;

   my $hi = int( $h / 60 );

   my $f = $h / 60 - $hi;

   my $p = $v * ( 1 - $s );
   my $q = $v * ( 1 - $f * $s );
   my $t = $v * ( 1 - ( 1 - $f ) * $s );

   my ( $r, $g, $b );

   if( $hi == 0 ) {
      ( $r, $g, $b ) = ( $v, $t, $p );
   }
   elsif( $hi == 1 ) {
      ( $r, $g, $b ) = ( $q, $v, $p );
   }
   elsif( $hi == 2 ) {
      ( $r, $g, $b ) = ( $p, $v, $t );
   }
   elsif( $hi == 3 ) {
      ( $r, $g, $b ) = ( $p, $q, $v );
   }
   elsif( $hi == 4 ) {
      ( $r, $g, $b ) = ( $t, $p, $v );
   }
   elsif( $hi == 5 ) {
      ( $r, $g, $b ) = ( $v, $p, $q );
   }

   return ( $r, $g, $b );
}

sub new_rgb
{
   my $class = shift;
   my ( $r, $g, $b ) = @_;

   my ( $hue, $min, $max ) = $class->_hue_min_max( $r, $g, $b );

   return $class->new(
      $hue,
      $max == 0 ? 0 : 1 - ( $min / $max ),
      $max
   );
}

=head2 dst_hsv

   $measure = $color->dst_hsv( $other )

Returns a measure of the distance between the two colors. This is the
Euclidean distance between the two colors as points in the chroma-adjusted
cone space.

=cut

sub dst_hsv
{
   my $self = shift;
   my ( $other ) = @_;

   # ... / sqrt(4)
   return sqrt( $self->dst_hsv_cheap( $other ) ) / 2;
}

=head2 dst_hsv_cheap

   $measure = $color->dst_hsv_cheap( $other )

Returns a measure of the distance between the two colors. This is used in the
calculation of C but since it omits the final square-root and scaling
it is cheaper to calculate, for use in cases where only the relative values
matter, such as when picking the "best match" out of a set of colors. It
ranges between 0 for identical colors and 4 for the distance between
complementary pure-saturated colors.

=cut

sub dst_hsv_cheap
{
   my $self = shift;
   my ( $other ) = @_;

   my $dv = $self->value - $other->value;

   return $self->_huechroma_dst_squ( $other ) + $dv*$dv;
}

=head1 SEE ALSO

=over 4

=item *

L - color space conversions

=item *

L - a color value represented as red/green/blue

=item *

L - HSL and HSV on Wikipedia

=back

=head1 AUTHOR

Paul Evans

=cut

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