Color::Calc(3) Simple calculations with RGB colors.

SYNOPSIS


use Color::Calc ();
my $background = 'green';
print 'background: ',Color::Calc::color_html($background),";\n";
print 'border-top: solid 1px ',Color::Calc::light_html($background),";\n";
print 'border-bottom: solid 1px ',Color::Calc::dark_html($background),";\n";
print 'color: ',Color::Calc::contrast_bw_html($background),";\n";

DESCRIPTION

The "Color::Calc" module implements simple calculations with RGB colors. This can be used to create a full color scheme from a few colors.

USAGE

Constructors
Color::Calc->new( ... )
This class method creates a new "Color::Calc" object. 

  use Color::Calc();
  my $cc = new Color::Calc( 'ColorScheme' => 'X', OutputFormat => 'HTML' );
  print $cc->invert( 'white' );

It accepts the following parameters:

ColorScheme
One of the color schemes accepted by "Graphics::ColorNames", which is used to interpret color names on input. Valid values include "X" (color names used in X-Windows) and "HTML" (color names defined in the HTML 4.0 specification). For a full list of possible values, please refer to the documentation of of "Graphics::ColorNames".

Unlike "Graphics::ColorNames", barewords are always interpreted as a module name under "Graphics::ColorNames". If you really want to use a filename like ``foo'', you have to write it as ``./foo''.

Default: "X" (Note: This is incompatible with HTML color names).

OutputFormat
One of the output formats defined by this module. Possible values are:
tuple
Returns a list of three values in the range 0..255. The first value is guaranteed to have a "length" that is not a multiple of three.
hex
Returns a hexadecimal RGB value as a scalar that contains a string in the format RRGGBB and a number representing the hexadecimal number 0xRRGGBB.
html
Returns a string compatible with W3C's HTML and CSS specifications, i.e. #RRGGBB or one of the sixteen HTML color names.
obj
(DEPRECATED) Returns a "Color::Object" reference. The module "Color::Object" must be installed, of course.
object
Returns a "Graphics::ColorObject" reference. The module "Graphics::ColorObject" must be installed, of course.
pdf
Returns a string compatible with "PDF::API2", i.e. #RRGGBB.
__MODEvar
(DEPRECATED) Uses the value of $Color::Calc::MODE to select one of the above output formats. You should use "local" when setting this variable: 

  local $Color::Calc::MODE = 'html';

Default: "__MODEvar" (for compatibility)

Color::Calc->import( ... )
This method creates a new, hidden object and binds its methods to the namespace of the calling module.

This method is usually not called directly but from perl's "use" statement: 

  use Color::Calc(
    'ColorScheme' => 'X',
    'OutputFormat' => 'HTML',
    'Prefix' => 'cc' );
  print cc_invert( 'white' );   # prints 'black'

On import, you can specify the following parameters:

ColorScheme
See above.
OutputFormat
See above.
Prefix
Adds a prefix to the front of the method names. The calculation methods are bound to the name prefix_method_name (the specified prefix, an underscore, the calculation method's name). Further, prefix is made an alias for prefix"_get".

Default: "color"

Please note that with perl's "use" and "import" statemehts, omitting the list and specifying an empty list has different meanings: 

  use Color::Calc;      # import with default settings (see below)
  use Color::Calc();    # don't import anything

Property ``set''/``get'' methods

These methods are inaccessible without a object reference, i.e. when the functions have been "import"ed.

$cc->set_output_format( $format)
Changes the output format for an existing "Color::Calc" object.

Calculation methods

All calculation methods always accept the following formats for $color or $color1/$color2:

  • An arrayref pointing to an array with three elements in the range 0..255 corresponding to the red, green, and blue component.
  • A list of three values in the range 0..255 corresponding to the red, green, and blue component where the first value does not have 3 or a multiple of 3 digits (e.g. "('0128',128,128)").
  • A string containing a hexadecimal RGB value like "#RGB"/"#RRGGBB"/"#RRRGGGBBB"/..., or "RGB"/"RRGGBB"/"RRRGGGBBB"/...
  • A color name accepted by "Graphics::ColorNames". The interpretation is controlled by the "ColorScheme" parameter.
  • A "Graphics::ColorObject" reference.

The calculation methods can be either accessed through a "Color::Calc" object reference (here: $cc) or through the method names imported by "import" (here using the prefix color).

$cc->get($color) / color($color)
Returns $color as-is (but in the selected output format). This function can be used for color format conversion/normalisation.
$cc->invert($color) / color_invert($color)
Returns the inverse of $color.
$cc->opposite($color) / color_opposite($color)
Returns a color that is on the opposite side of the color wheel but roughly keeps the saturation and lightness.
$cc->bw($color) / color_bw($color)
$cc->grey($color) / color_grey($color)
$cc->gray($color) / color_gray($color)
Converts $color to greyscale.
$cc->round($color, $value_count) / color_round($color, $value_count)
Rounds each component to to the nearest number determined by dividing the range 0..255 into $value_count+1 portions.

The default for $value_count is 6, yielding 6^3 = 216 colors. Values that are one higher than divisors of 255 yield the best results (e.g. 3+1, 5+1, 7+1, 9+1, 15+1, 17+1, ...).

$cc->safe($color) / color_safe($color)
Rounds each color component to a multiple of 0x33 (dec. 51) or to a named color defined in the HTML 4.01 specification.

Historically, these colors have been known as web-safe colors. They still provide a convenient color palette.

$cc->mix($color1, $color2 [, $alpha]) / color_mix($color1, $color2 [, $alpha])
Returns a color that is the mixture of $color1 and $color2.

The optional $alpha parameter can be a value between 0.0 (use $color1 only) and 1.0 (use $color2 only), the default is 0.5.

$cc->light($color [, $alpha]) / color_light($color [, $alpha])
Returns a lighter version of $color, i.e. returns "mix($color,[255,255,255],$alpha)".

The optional $alpha parameter can be a value between 0.0 (use $color only) and 1.0 (use [255,255,255] only), the default is 0.5.

$cc->dark($color [, $alpha]) / color_dark($color [, $alpha])
Returns a darker version of $color, i.e. returns "mix($color,[0,0,0],$alpha)".

The optional $alpha parameter can be a value between 0.0 (use $color only) and 1.0 (use [0,0,0] only), the default is 0.5.

$cc->contrast($color [, $cut]) / color_contrast($color [, $cut])
Returns a color that has the highest possible contrast to the input color.

This is done by setting the red, green, and blue values to 0 if the corresponding value in the input is above "($cut * 255)" and to 255 otherwise.

The default for $cut is .5, representing a cutoff between 127 and 128.

$cc->contrast_bw($color [, $cut]) / color_contrast_bw($color [, $cut])
Returns black or white, whichever has the higher contrast to $color.

This is done by returning black if the grey value of $color is above "($cut * 255)" and white otherwise.

The default for $cut is .5, representing a cutoff between 127 and 128.

$cc->blend($color [, $alpha]) / color_blend($color [, $alpha])
Returns a color that blends into the background, i.e. it returns "mix($color,contrast($color),$alpha)".

The optional $alpha parameter can be a value between 0.0 (use $color only) and 1.0 (use "contrast($color)" only), the default is 0.5.

The idea is that $color is the foreground color, so "contrast($color)" is similar to the background color. Mixing them returns a color somewhere between them.

You might want to use "mix($color, $background, $alpha)" instead if you know the real background color.

$cc->blend_bw($color [, $alpha]) / color_blend_bw($color [, $alpha])
Returns a mix of $color and black or white, whichever has the higher contrast to $color.

The optional $alpha parameter can be a value between 0.0 (use $color only) and 1.0 (use black/white only), the default is 0.5.

Functions

The calculation methods are also available as functions. The output format is selected through the function name.

These functions are deprecated as they do not allow selecting the scheme of recognized color names, which defaults to Graphics::ColorNames::X (and is incompatible with HTML's color names).

By default, i.e. when no list is specified with "use" or "import", all of these functions are exported.

color, color_mix, ...
Use $Color::Calc::MODE as the output format. This is the default.
color_hex, color_mix_html, ...
Use "hex" as the output format.
color_html, color_mix_html, ...
Use "html" as the output format. Please note that the color names recognized are still based on X's color names, which are incompatible with HTML. You can't use the output of these functions as input for other color_*_html functions.

See Color::Calc::WWW for an alternative that does not suffer from this problem.

color_pdf, color_mix_pdf, ...
Use "pdf" as the output format.
color_object, color_mix_object, ...
Use "object" as the output format.

AUTHOR

Claus Fa.rber <[email protected]>

LICENSE

Copyright 2004-2010 Claus Fa.rber. All rights reserved.

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

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