Class: Spectrum::CMYK

Inherits:
Object
  • Object
show all
Defined in:
lib/spectrum/cmyk.rb,
lib/spectrum.rb

Overview

An CMYK colour object. CMYK (cyan, magenta, yellow, and black) colours are based on additive percentages of ink. A CMYK colour of (0.3, 0, 0.8, 0.3) would be mixed from 30% cyan, 0% magenta, 80% yellow, and 30% black. Primarily used in four-colour printing processes.

Constant Summary collapse

PDF_FORMAT_STR =

The format of a DeviceCMYK 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 %.3f %.3f %.3f %s"

Class Method Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(c = 0, m = 0, y = 0, k = 0) ⇒ CMYK

Creates a CMYK colour object from percentages. Internally, the colour is managed as fractional values 0..1.

Spectrum::CMYK.new(30, 0, 80, 30)



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# File 'lib/spectrum/cmyk.rb', line 65

def initialize(c = 0, m = 0, y = 0, k = 0)
  @c = c / 100.0
  @m = m / 100.0
  @y = y / 100.0
  @k = k / 100.0
end

Class Method Details

.from_fraction(c = 0, m = 0, y = 0, k = 0) ⇒ Object

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

Spectrum::CMYK.from_fraction(0.3, 0, 0.8, 0.3)



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# File 'lib/spectrum/cmyk.rb', line 44

def self.from_fraction(c = 0, m = 0, y = 0, k = 0)
  colour = Spectrum::CMYK.new
  colour.c = c
  colour.m = m
  colour.y = y
  colour.k = k
  colour
end

.from_percent(c = 0, m = 0, y = 0, k = 0) ⇒ Object

Creates a CMYK colour object from percentages. Internally, the colour is managed as fractional values 0..1.

Spectrum::CMYK.new(30, 0, 80, 30)



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# File 'lib/spectrum/cmyk.rb', line 57

def self.from_percent(c = 0, m = 0, y = 0, k = 0)
  Spectrum::CMYK.new(c, m, y, k)
end

Instance Method Details

#==(other) ⇒ Object

Compares the other colour to this one. The other colour will be converted to CMYK before comparison, so the comparison between a CMYK colour and a non-CMYK colour will be approximate and based on the other colour’s #to_cmyk conversion. If there is no #to_cmyk conversion, this will raise an exception. This will report that two CMYK colours are equivalent if all component values are within COLOR_TOLERANCE of each other.



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# File 'lib/spectrum/cmyk.rb', line 32

def ==(other)
  other = other.to_cmyk
  other.kind_of?(Spectrum::CMYK) and
  ((@c - other.c).abs <= Spectrum::COLOR_TOLERANCE) and
  ((@m - other.m).abs <= Spectrum::COLOR_TOLERANCE) and
  ((@y - other.y).abs <= Spectrum::COLOR_TOLERANCE) and
  ((@k - other.k).abs <= Spectrum::COLOR_TOLERANCE)
end

#black ⇒ Object

Returns the black (K) component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 264

def black
  @k * 100.0
end

#black=(kk) ⇒ Object

Sets the black (K) component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 273

def black=(kk)
  @k = Spectrum.normalize(kk / 100.0)
end

#c ⇒ Object

Returns the cyan © component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 209

def c
  @c
end

#c=(cc) ⇒ Object

Sets the cyan © component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 218

def c=(cc)
  @c = Spectrum.normalize(cc)
end

#css_hsl ⇒ Object

Present the colour as an HSL HTML/CSS colour string (e.g., “hsl(180, 25%, 35%)”). Note that this will perform a #to_hsl operation using the default conversion formula.



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# File 'lib/spectrum/cmyk.rb', line 108

def css_hsl
  to_hsl.css_hsl
end

#css_hsla ⇒ Object

Present the colour as an HSLA (with alpha) HTML/CSS colour string (e.g., “hsla(180, 25%, 35%, 1)”). Note that this will perform a #to_hsl operation using the default conversion formula.



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# File 'lib/spectrum/cmyk.rb', line 115

def css_hsla
  to_hsl.css_hsla
end

#css_rgb ⇒ Object

Present the colour as an RGB HTML/CSS colour string (e.g., “rgb(0%, 50%, 100%)”). Note that this will perform a #to_rgb operation using the default conversion formula.



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# File 'lib/spectrum/cmyk.rb', line 94

def css_rgb
  to_rgb.css_rgb
end

#css_rgba ⇒ Object

Present the colour as an RGBA (with alpha) HTML/CSS colour string (e.g., “rgb(0%, 50%, 100%, 1)”). Note that this will perform a #to_rgb operation using the default conversion formula.



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# File 'lib/spectrum/cmyk.rb', line 101

def css_rgba
  to_rgb.css_rgba
end

#cyan ⇒ Object

Returns the cyan © component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 204

def cyan
  @c * 100.0
end

#cyan=(cc) ⇒ Object

Sets the cyan © component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 213

def cyan=(cc)
  @c = Spectrum.normalize(cc / 100.0)
end

#html ⇒ Object

Present the colour as an RGB HTML/CSS colour string (e.g., “#aabbcc”). Note that this will perform a #to_rgb operation using the default conversion formula.



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# File 'lib/spectrum/cmyk.rb', line 87

def html
  to_rgb.html
end

#inspect ⇒ Object 



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# File 'lib/spectrum/cmyk.rb', line 189

def inspect
  "CMYK [%.2f%%, %.2f%%, %.2f%%, %.2f%%]" % [ cyan, magenta, yellow, black ]
end

#k ⇒ Object

Returns the black (K) component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 269

def k
  @k
end

#k=(kk) ⇒ Object

Sets the black (K) component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 278

def k=(kk)
  @k = Spectrum.normalize(kk)
end

#m ⇒ Object

Returns the magenta (M) component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 229

def m
  @m
end

#m=(mm) ⇒ Object

Sets the magenta (M) component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 238

def m=(mm)
  @m = Spectrum.normalize(mm)
end

#magenta ⇒ Object

Returns the magenta (M) component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 224

def magenta
  @m * 100.0
end

#magenta=(mm) ⇒ Object

Sets the magenta (M) component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 233

def magenta=(mm)
  @m = Spectrum.normalize(mm / 100.0)
end

#pdf_fill ⇒ Object

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



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# File 'lib/spectrum/cmyk.rb', line 74

def pdf_fill
  PDF_FORMAT_STR % [ @c, @m, @y, @k, "k" ]
end

#pdf_stroke ⇒ Object

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



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# File 'lib/spectrum/cmyk.rb', line 80

def pdf_stroke
  PDF_FORMAT_STR % [ @c, @m, @y, @k, "K" ]
end

#to_cmyk ⇒ Object 



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# File 'lib/spectrum/cmyk.rb', line 185

def to_cmyk
  self
end

#to_grayscale ⇒ Object Also known as: to_greyscale

Converts the CMYK colour to a single greyscale value. There are undoubtedly multiple methods for this conversion, but only a minor variant of the Adobe conversion method will be used:

g = 1.0 - min(1.0, 0.299 * c + 0.587 * m + 0.114 * y + k)

This treats the CMY values similarly to YIQ (NTSC) values and then adds the level of black. This is a variant of the Adobe version because it uses the more precise YIQ (NTSC) conversion values for Y (intensity) rather than the approximates provided by Adobe (0.3, 0.59, and 0.11).



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# File 'lib/spectrum/cmyk.rb', line 176

def to_grayscale
  c = 0.299 * @c.to_f
  m = 0.587 * @m.to_f
  y = 0.114 * @y.to_f
  g = 1.0 - [1.0, c + m + y + @k].min
  Spectrum::GrayScale.from_fraction(g)
end

#to_hsl ⇒ Object

Converts to RGB then HSL.



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# File 'lib/spectrum/cmyk.rb', line 199

def to_hsl
  to_rgb.to_hsl
end

#to_rgb(use_adobe_method = false) ⇒ Object

Converts the CMYK colour to RGB. Most colour experts strongly suggest that this is not a good idea (some even suggesting that it’s a very bad idea). CMYK represents additive percentages of inks on white paper, whereas RGB represents mixed colour intensities on a black screen.

However, the colour conversion can be done, and there are two different methods for the conversion that provide slightly different results. Adobe PDF conversions are done with the first form.

  # Adobe PDF Display Formula
r = 1.0 - min(1.0, c + k)
g = 1.0 - min(1.0, m + k)
b = 1.0 - min(1.0, y + k)

  # Other
r = 1.0 - (c * (1.0 - k) + k)
g = 1.0 - (m * (1.0 - k) + k)
b = 1.0 - (y * (1.0 - k) + k)

If we have a CMYK colour of [33% 66% 83% 25%], the first method will give an approximate RGB colour of (107, 23, 0) or #6b1700. The second method will give an approximate RGB colour of (128, 65, 33) or #804121. Which is correct? Although the colours may seem to be drastically different in the RGB colour space, they are very similar colours, differing mostly in intensity. The first is a darker, slightly redder brown; the second is a lighter brown.

Because of this subtlety, both methods are now offered for conversion. The Adobe method is not used by default; to enable it, pass true to #to_rgb.

Future versions of Spectrum may offer other conversion mechanisms that offer greater colour fidelity, including recognition of ICC colour profiles.



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# File 'lib/spectrum/cmyk.rb', line 153

def to_rgb(use_adobe_method = false)
  if use_adobe_method
    r = 1.0 - [1.0, @c + @k].min
    g = 1.0 - [1.0, @m + @k].min
    b = 1.0 - [1.0, @y + @k].min
  else
    r = 1.0 - (@c.to_f * (1.0 - @k.to_f) + @k.to_f)
    g = 1.0 - (@m.to_f * (1.0 - @k.to_f) + @k.to_f)
    b = 1.0 - (@y.to_f * (1.0 - @k.to_f) + @k.to_f)
  end
  Spectrum::RGB.from_fraction(r, g, b)
end

#to_yiq ⇒ Object

Converts to RGB then YIQ.



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# File 'lib/spectrum/cmyk.rb', line 194

def to_yiq
  to_rgb.to_yiq
end

#y ⇒ Object

Returns the yellow (Y) component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 249

def y
  @y
end

#y=(kk) ⇒ Object

Sets the yellow (Y) component of the CMYK colour as a value in the range 0.0 .. 1.0.



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# File 'lib/spectrum/cmyk.rb', line 258

def y=(kk)
  @y = Spectrum.normalize(kk)
end

#yellow ⇒ Object

Returns the yellow (Y) component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 244

def yellow
  @y * 100.0
end

#yellow=(yy) ⇒ Object

Sets the yellow (Y) component of the CMYK colour as a percentage value.



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# File 'lib/spectrum/cmyk.rb', line 253

def yellow=(yy)
  @y = Spectrum.normalize(yy / 100.0)
end