Class: Color::CMYK

Inherits:
Object
  • Object
show all
Includes:
Color
Defined in:
lib/color/cmyk.rb,
lib/color.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"

Constants included from Color

COLOR_EPSILON, COLOR_TOLERANCE, COLOR_VERSION

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Color

#==, coerce, const_missing, equivalent?, #name, #names, #names=, near?, near_one?, near_one_or_more?, near_zero?, near_zero_or_less?, new, normalize, normalize_byte, normalize_to_range, normalize_word

Constructor Details

#initialize(c = 0, m = 0, y = 0, k = 0, radix = 100.0, &block) ⇒ CMYK

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

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

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# File 'lib/color/cmyk.rb', line 39

def initialize(c = 0, m = 0, y = 0, k = 0, radix = 100.0, &block) # :yields self:
  @c, @m, @y, @k = [ c, m, y, k ].map { |v| Color.normalize(v / radix) }
  block.call(self) if block
end

Class Method Details

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

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

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

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# File 'lib/color/cmyk.rb', line 22

def from_fraction(c = 0, m = 0, y = 0, k = 0, &block)
  new(c, m, y, k, 1.0, &block)
end

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

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

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

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# File 'lib/color/cmyk.rb', line 30

def from_percent(c = 0, m = 0, y = 0, k = 0, &block)
  new(c, m, y, k, &block)
end

Instance Method Details

#blackObject

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


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# File 'lib/color/cmyk.rb', line 231

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/color/cmyk.rb', line 240

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

#cObject

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


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

def c
  @c
end

#c=(cc) ⇒ Object

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


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

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

#coerce(other) ⇒ Object

Coerces the other Color object into CMYK.


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# File 'lib/color/cmyk.rb', line 14

def coerce(other)
  other.to_cmyk
end

#css_hslObject

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/color/cmyk.rb', line 80

def css_hsl
  to_hsl.css_hsl
end

#css_hslaObject

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/color/cmyk.rb', line 87

def css_hsla
  to_hsl.css_hsla
end

#css_rgbObject

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/color/cmyk.rb', line 66

def css_rgb
  to_rgb.css_rgb
end

#css_rgbaObject

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/color/cmyk.rb', line 73

def css_rgba
  to_rgb.css_rgba
end

#cyanObject

Returns the cyan (C) component of the CMYK colour as a percentage value.


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# File 'lib/color/cmyk.rb', line 171

def cyan
  @c * 100.0
end

#cyan=(cc) ⇒ Object

Sets the cyan (C) component of the CMYK colour as a percentage value.


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# File 'lib/color/cmyk.rb', line 180

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

#htmlObject

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/color/cmyk.rb', line 59

def html
  to_rgb.html
end

#inspectObject


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# File 'lib/color/cmyk.rb', line 156

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

#kObject

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/color/cmyk.rb', line 236

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/color/cmyk.rb', line 245

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

#mObject

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/color/cmyk.rb', line 196

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/color/cmyk.rb', line 205

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

#magentaObject

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


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# File 'lib/color/cmyk.rb', line 191

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/color/cmyk.rb', line 200

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

#pdf_fillObject

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/color/cmyk.rb', line 46

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

#pdf_strokeObject

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/color/cmyk.rb', line 52

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

#to_aObject


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

def to_a
  [ c, m, y, k ]
end

#to_cmykObject


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# File 'lib/color/cmyk.rb', line 152

def to_cmyk
  self
end

#to_grayscaleObject 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/color/cmyk.rb', line 143

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
  Color::GrayScale.from_fraction(g)
end

#to_hslObject

Converts to RGB then HSL.


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# File 'lib/color/cmyk.rb', line 166

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


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# File 'lib/color/cmyk.rb', line 125

def to_rgb(use_adobe_method = false)
  if use_adobe_method
    Color::RGB.from_fraction(*adobe_cmyk_rgb)
  else
    Color::RGB.from_fraction(*standard_cmyk_rgb)
  end
end

#to_yiqObject

Converts to RGB then YIQ.


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# File 'lib/color/cmyk.rb', line 161

def to_yiq
  to_rgb.to_yiq
end

#yObject

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/color/cmyk.rb', line 216

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/color/cmyk.rb', line 225

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

#yellowObject

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


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# File 'lib/color/cmyk.rb', line 211

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/color/cmyk.rb', line 220

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