Class: Color::GrayScale

Inherits:
Object
  • Object
show all
Defined in:
lib/color/grayscale.rb,
lib/color.rb

Overview

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

Constant Summary collapse

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.

"%.3f %s"

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(g = 0) ⇒ GrayScale

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

Color::GrayScale.new(50)



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# File 'lib/color/grayscale.rb', line 32

def initialize(g = 0)
  @g = g / 100.0
end

Instance Attribute Details

#g ⇒ Object

Returns the value of attribute g.



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# File 'lib/color/grayscale.rb', line 123

def g
  @g
end

Class Method Details

.from_fraction(g = 0) ⇒ Object

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

Color::GreyScale.from_fraction(0.5)



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# File 'lib/color/grayscale.rb', line 23

def self.from_fraction(g = 0)
  color = Color::GrayScale.new
  color.g = g
  color
end

Instance Method Details

#==(other) ⇒ Object

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.



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# 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 ⇒ Object

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



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# File 'lib/color/grayscale.rb', line 119

def brightness
  @g
end

#darken_by(percent) ⇒ Object

Darken the RGB hue by the stated percent.



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# 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 ⇒ Object

Present the colour as an HTML/CSS colour string.



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# File 'lib/color/grayscale.rb', line 67

def html
  gs = "%02x" % to_255
  "##{gs * 3}"
end

#lighten_by(percent) ⇒ Object

Lightens the greyscale colour by the stated percent.



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# 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 ⇒ Object

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



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# File 'lib/color/grayscale.rb', line 51

def pdf_fill
  PDF_FORMAT_STR % [ @g, "g" ]
end

#pdf_stroke ⇒ Object

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



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# File 'lib/color/grayscale.rb', line 57

def pdf_stroke
  PDF_FORMAT_STR % [ @g, "G" ]
end

#to_cmyk ⇒ Object

Convert the greyscale colour to CMYK.



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# 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 ⇒ Object Also known as: to_greyscale 



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# File 'lib/color/grayscale.rb', line 84

def to_grayscale
  self
end

#to_hsl ⇒ Object

Returns the HSL colour encoding of the greyscale value.



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# File 'lib/color/grayscale.rb', line 113

def to_hsl
  Color::HSL.from_fraction(0, 0, @g)
end

#to_rgb(ignored = true) ⇒ Object

Convert the greyscale colour to RGB.



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# File 'lib/color/grayscale.rb', line 79

def to_rgb(ignored = true)
  g = to_255
  Color::RGB.new(g, g, g)
end

#to_yiq ⇒ Object

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.



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# 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