class GreyScale

A colour object representing shades of grey. Used primarily in PDF document creation.

Constants

PDF_FORMAT_STR

The format of a DeviceGrey colour for PDF. In color-tools 2.0 this will be removed from this package and added back as a modification by the PDF::Writer package.

Attributes

g[RW]

Public Class Methods

from_fraction(g = 0) click to toggle source

Creates a greyscale colour object from fractional values 0..1.

Color::GreyScale.from_fraction(0.5)
# File lib/color/grayscale.rb, line 23
def self.from_fraction(g = 0)
  color = Color::GrayScale.new
  color.g = g
  color
end
new(g = 0) click to toggle source

Creates a greyscale colour object from percentages 0..100.

Color::GrayScale.new(50)
# File lib/color/grayscale.rb, line 32
def initialize(g = 0)
  @g = g / 100.0
end

Public Instance Methods

==(other) click to toggle source

Compares the other colour to this one. The other colour will be converted to GreyScale before comparison, so the comparison between a GreyScale colour and a non-GreyScale colour will be approximate and based on the other colour's to_greyscale conversion. If there is no to_greyscale conversion, this will raise an exception. This will report that two GreyScale values are equivalent if they are within 1e-4 (0.0001) of each other.

# File lib/color/grayscale.rb, line 43
def ==(other)
  other = other.to_grayscale
  other.kind_of?(Color::GrayScale) and
  ((@g - other.g).abs <= 1e-4)
end
brightness() click to toggle source

Returns the brightness value for this greyscale value; this is the greyscale value.

# File lib/color/grayscale.rb, line 119
def brightness
  @g
end
darken_by(percent) click to toggle source

Darken the RGB hue by the stated percent.

# File lib/color/grayscale.rb, line 96
def darken_by(percent)
  g = [@g - (@g * (percent / 100.0)), 0.0].max
  Color::GrayScale.from_fraction(g)
end
html() click to toggle source

Present the colour as an HTML/CSS colour string.

# File lib/color/grayscale.rb, line 67
def html
  gs = "%02x" % to_255
  "##{gs * 3}"
end
lighten_by(percent) click to toggle source

Lightens the greyscale colour by the stated percent.

# File lib/color/grayscale.rb, line 90
def lighten_by(percent)
  g = [@g + (@g * (percent / 100.0)), 1.0].min
  Color::GrayScale.from_fraction(g)
end
pdf_fill() click to toggle source

Present the colour as a DeviceGrey fill colour string for PDF. This will be removed from the default package in color-tools 2.0.

# File lib/color/grayscale.rb, line 51
def pdf_fill
  PDF_FORMAT_STR % [ @g, "g" ]
end
pdf_stroke() click to toggle source

Present the colour as a DeviceGrey stroke colour string for PDF. This will be removed from the default package in color-tools 2.0.

# File lib/color/grayscale.rb, line 57
def pdf_stroke
  PDF_FORMAT_STR % [ @g, "G" ]
end
to_cmyk() click to toggle source

Convert the greyscale colour to CMYK.

# File lib/color/grayscale.rb, line 73
def to_cmyk
  k = 1.0 - @g.to_f
  Color::CMYK.from_fraction(0, 0, 0, k)
end
to_grayscale() click to toggle source
# File lib/color/grayscale.rb, line 84
def to_grayscale
  self
end
Also aliased as: to_greyscale
to_greyscale()
Alias for: to_grayscale
to_hsl() click to toggle source

Returns the HSL colour encoding of the greyscale value.

# File lib/color/grayscale.rb, line 113
def to_hsl
  Color::HSL.from_fraction(0, 0, @g)
end
to_rgb(ignored = true) click to toggle source

Convert the greyscale colour to RGB.

# File lib/color/grayscale.rb, line 79
def to_rgb(ignored = true)
  g = to_255
  Color::RGB.new(g, g, g)
end
to_yiq() click to toggle source

Returns the YIQ (NTSC) colour encoding of the greyscale value. This is an approximation, as the values for I and Q are calculated by treating the greyscale value as an RGB value. The Y (intensity or brightness) value is the same as the greyscale value.

# File lib/color/grayscale.rb, line 105
def to_yiq
  y = @g
  i = (@g * 0.596) + (@g * -0.275) + (@g * -0.321)
  q = (@g * 0.212) + (@g * -0.523) + (@g *  0.311)
  Color::YIQ.from_fraction(y, i, q)
end

Private Instance Methods

to_255() click to toggle source
# File lib/color/grayscale.rb, line 61
def to_255
  [(@g * 255).round, 255].min
end