Convert::Color(3) color space conversions and named lookups

SYNOPSIS


use Convert::Color;
my $color = Convert::Color->new( 'hsv:76,0.43,0.89' );
my ( $red, $green, $blue ) = $color->rgb;
# GTK uses 16-bit values
my $gtk_col = Gtk2::Gdk::Color->new( $color->as_rgb16->rgb16 );
# HTML uses #rrggbb in hex
my $html = '<td bgcolor="#' . $color->as_rgb8->hex . '">';

DESCRIPTION

This module provides conversions between commonly used ways to express colors. It provides conversions between color spaces such as RGB and HSV, and it provides ways to look up colors by a name.

This class provides a base for subclasses which represent particular color values in particular spaces. The base class provides methods to represent the color in a few convenient forms, though subclasses may provide more specific details for the space in question.

For more detail, read the documentation on these classes; namely:

  • Convert::Color::RGB - red/green/blue as floats between 0 and 1
  • Convert::Color::RGB8 - red/green/blue as 8-bit integers
  • Convert::Color::RGB16 - red/green/blue as 16-bit integers
  • Convert::Color::HSV - hue/saturation/value
  • Convert::Color::HSL - hue/saturation/lightness
  • Convert::Color::CMY - cyan/magenta/yellow
  • Convert::Color::CMYK - cyan/magenta/yellow/key (blackness)

The following classes are subclasses of one of the above, which provide a way to access predefined colors by names:

  • Convert::Color::VGA - named lookup for the basic VGA colors
  • Convert::Color::X11 - named lookup of colors from X11's rgb.txt

CONSTRUCTOR

$color = Convert::Color->new( STRING )

Return a new value to represent the color specified by the string. This string should be prefixed by the name of the color space to which it applies. For example 

 rgb:RED,GREEN,BLUE
 rgb8:RRGGBB
 rgb16:RRRRGGGGBBBB
 hsv:HUE,SAT,VAL
 hsl:HUE,SAT,LUM
 cmy:CYAN,MAGENTA,YELLOW
 cmyk:CYAN,MAGENTA,YELLOW,KEY
 vga:NAME
 vga:INDEX
 x11:NAME

For more detail, see the constructor of the color space subclass in question.

METHODS

( $red, $green, $blue ) = $color->rgb

Returns the individual red, green and blue color components of the color value. For RGB values, this is done directly. For values in other spaces, this is done by first converting them to an RGB value using their "to_rgb()" method.

COLOR SPACE CONVERSIONS

Cross-conversion between color spaces is provided by the "convert_to()" method, assisted by helper methods in the two color space classes involved.

When converting $color from color space SRC to color space DEST, the following operations are attemped, in this order. SRC and DEST refer to the names of the color spaces, e.g. "rgb".

1.
If SRC and DEST are equal, return $color as it stands.
2.
If the SRC space's class provides a "convert_to_DEST" method, use it.
3.
If the DEST space's class provides a "new_from_SRC" constructor, call it and pass $color.
4.
If the DEST space's class provides a "new_rgb" constructor, convert $color to red/green/blue components then call it.
5.
If none of these operations worked, then throw an exception.

These functions may be called in the following ways: 

 $other = $color->convert_to_DEST()
 $other = Dest::Class->new_from_SRC( $color )
 $other = Dest::Class->new_rgb( $color->rgb )

$other = $color->convert_to( $space )

Attempt to convert the color into its representation in the given space. See above for the various ways this may be achieved.

If the relevant subclass has already been loaded (either explicitly, or implicitly by either the "new" or "convert_to" methods), then a specific conversion method will be installed in the class. 

 $other = $color->as_$space

Methods of this form are currently "AUTOLOAD"ed if they do not yet exist, but this feature should not be relied upon - see below.

AUTOLOADED CONVERSION METHODS

This class provides "AUTOLOAD" and "can" behaviour which automatically constructs conversion methods. The following method calls are identical: 

 $color->convert_to('rgb')
 $color->as_rgb

The generated method will be stored in the package, so that future calls will not have the AUTOLOAD overhead.

This feature is deprecated and should not be relied upon, due to the delicate nature of "AUTOLOAD".

OTHER METHODS

As well as the above, it is likely the subclass will provide accessors to directly obtain the components of its representation in the specific space. For more detail, see the documentation for the specific subclass in question.

SUBCLASS METHODS

This base class is intended to be subclassed to provide more color spaces.

$class->register_color_space( $space )

A subclass should call this method to register itself as a named color space.

$class->register_palette( %args )

A subclass that provides a fixed set of color values should call this method, to set up automatic conversions that look for the closest match within the set. This conversion process is controlled by the %args:
enumerate => STRING or CODE
A method name or anonymous CODE reference which will be used to generate the list of color values.
enumerate_once => STRING or CODE
As per "enumerate", but will be called only once and the results cached.

This method creates a new class method on the calling package, called "closest_to".

$color = $pkg->closest_to( $orig, $space )

Returns the color in the space closest to the given value. The distance is measured in the named space; defaulting to "rgb" if this is not provided.

In the case of a tie, where two or more colors have the same distance from the target, the first one will be chosen.

AUTHOR

Paul Evans <[email protected]>

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