NAME

"Convert::Color::HSL" - a color value represented as hue/saturation/lightness

SYNOPSIS

Directly:

 use Convert::Color::HSL;

 my $red = Convert::Color::HSL->new( 0, 1, 0.5 );

 # Can also parse strings
 my $pink = Convert::Color::HSL->new( '0,1,0.8' );

Via Convert::Color:

 use Convert::Color;

 my $cyan = Convert::Color->new( 'hsl:300,1,0.5' );

DESCRIPTION

Objects in this class represent a color in HSL 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 lightness 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 as the distance from the axis, and the lightness 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 entire top of the cylinder is pure white. The circumference of the circular cross-section midway along the axis contains the pure-saturated color wheel.

Because both surfaces of this cylinder contain pure black or white discs, a closely-related color space can be created by reshaping the cylinder into a bi-cone such that the top and bottom of the cylinder become single points. The radius from the axis of this shape is called the chroma (though this is a different definition of "chroma" than that used by CIE).

While the components of this space are called Hue-Chroma-Lightness, it should not be confused with the similarly-named Hue-Chroma-Luminance (HCL) space.

CONSTRUCTOR

$color = Convert::Color::HSL->new( $hue, $saturation, $lightness )

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 lightness should be between 0 and 1. Values outside of these ranges will be clamped.

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

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

 hue,saturation,lightnes

containing the three floating-point values in decimal notation.

METHODS

$h = $color->hue

$s = $color->saturation

$v = $color->lightness

Accessors for the three components of the color.

$c = $color->chroma

Returns the derived property of "chroma", which maps the color space onto a bicone 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.

( $hue, $saturation, $lightness ) = $color->hsl

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

$measure = $color->dst_hsl( $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.

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

Returns a measure of the distance between the two colors. This is used in the calculation of "dst_hsl" 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.

AUTHOR

Paul Evans <leonerd@leonerd.org.uk>