class Color::CMYK
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.
Constants
- 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.
Public Class Methods
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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
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 30 def from_percent(c = 0, m = 0, y = 0, k = 0, &block) new(c, m, y, k, &block) end
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
Creates a CMYK
colour object from percentages. Internally, the colour is managed as fractional values 0..1.
Color::CMYK.new(30, 0, 80, 30)
Public Instance Methods
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# File lib/color/cmyk.rb, line 231 def black @k * 100.0 end
Returns 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
Sets the black (K) component of the CMYK
colour as a percentage value.
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# File lib/color/cmyk.rb, line 176 def c @c end
Returns the cyan © 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
Sets the cyan © 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 80 def css_hsl to_hsl.css_hsl end
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 87 def css_hsla to_hsl.css_hsla end
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 66 def css_rgb to_rgb.css_rgb end
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 73 def css_rgba(alpha = 1) to_rgb.css_rgba(alpha) end
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 171 def cyan @c * 100.0 end
Returns the cyan © 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
Sets the cyan © component of the CMYK
colour as a percentage value.
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# File lib/color/cmyk.rb, line 59 def html to_rgb.html end
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 156 def inspect "CMYK [%.2f%%, %.2f%%, %.2f%%, %.2f%%]" % [ cyan, magenta, yellow, black ] end
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# File lib/color/cmyk.rb, line 236 def k @k end
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 245 def k=(kk) @k = Color.normalize(kk) end
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 196 def m @m end
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 205 def m=(mm) @m = Color.normalize(mm) end
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 191 def magenta @m * 100.0 end
Returns 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
Sets the magenta (M) component of the CMYK
colour as a percentage value.
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# File lib/color/cmyk.rb, line 46 def pdf_fill PDF_FORMAT_STR % [ @c, @m, @y, @k, "k" ] end
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 52 def pdf_stroke PDF_FORMAT_STR % [ @c, @m, @y, @k, "K" ] end
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 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
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 166 def to_hsl to_rgb.to_hsl end
Converts to RGB then HSL.
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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
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 161 def to_yiq to_rgb.to_yiq end
Converts to RGB then YIQ.
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# File lib/color/cmyk.rb, line 216 def y @y end
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 225 def y=(kk) @y = Color.normalize(kk) end
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 211 def yellow @y * 100.0 end
Returns 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
Sets the yellow (Y) component of the CMYK
colour as a percentage value.
Private Instance Methods
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# File lib/color/cmyk.rb, line 255 def adobe_cmyk_rgb [ @c, @m, @y ].map { |v| 1.0 - [ 1.0, v + @k ].min } end
Implements the Adobe PDF conversion of CMYK
to RGB.
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# File lib/color/cmyk.rb, line 260 def standard_cmyk_rgb [ @c, @m, @y ].map { |v| 1.0 - (v * (1.0 - k) + k) } end
Implements the standard conversion of CMYK
to RGB.