Class: Color::CMYK
- Inherits:
-
Object
- Object
- Color::CMYK
- 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.
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"
Instance Attribute Summary collapse
-
#c ⇒ Object
Returns the value of attribute c.
-
#k ⇒ Object
Returns the value of attribute k.
-
#m ⇒ Object
Returns the value of attribute m.
-
#y ⇒ Object
Returns the value of attribute y.
Class Method Summary collapse
-
.from_fraction(c = 0, m = 0, y = 0, k = 0) ⇒ Object
Creates a CMYK colour object from fractional values 0..1.
Instance Method Summary collapse
-
#==(other) ⇒ Object
Compares the other colour to this one.
-
#html ⇒ Object
Present the colour as an RGB HTML/CSS colour string.
-
#initialize(c = 0, m = 0, y = 0, k = 0) ⇒ CMYK
constructor
Creates a CMYK colour object from percentages.
-
#pdf_fill ⇒ Object
Present the colour as a DeviceCMYK fill colour string for PDF.
-
#pdf_stroke ⇒ Object
Present the colour as a DeviceCMYK stroke colour string for PDF.
- #to_cmyk ⇒ Object
-
#to_grayscale ⇒ Object
(also: #to_greyscale)
Converts the CMYK colour to a single greyscale value.
-
#to_hsl ⇒ Object
Converts to RGB then HSL.
-
#to_rgb(use_adobe_method = false) ⇒ Object
Converts the CMYK colour to RGB.
-
#to_yiq ⇒ Object
Converts to RGB then YIQ.
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.
Color::CMYK.from_fraction(30, 0, 80, 30)
54 55 56 57 58 59 |
# File 'lib/color/cmyk.rb', line 54 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 |
Instance Attribute Details
#c ⇒ Object
Returns the value of attribute c.
160 161 162 |
# File 'lib/color/cmyk.rb', line 160 def c @c end |
#k ⇒ Object
Returns the value of attribute k.
160 161 162 |
# File 'lib/color/cmyk.rb', line 160 def k @k end |
#m ⇒ Object
Returns the value of attribute m.
160 161 162 |
# File 'lib/color/cmyk.rb', line 160 def m @m end |
#y ⇒ Object
Returns the value of attribute y.
160 161 162 |
# File 'lib/color/cmyk.rb', line 160 def y @y end |
Class Method Details
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 1e-4 (0.0001) of each other.
29 30 31 32 33 34 35 36 |
# File 'lib/color/cmyk.rb', line 29 def ==(other) other = other.to_cmyk other.kind_of?(Color::CMYK) and ((@c - other.c).abs <= 1e-4) and ((@m - other.m).abs <= 1e-4) and ((@y - other.y).abs <= 1e-4) and ((@k - other.k).abs <= 1e-4) end |
#html ⇒ Object
Present the colour as an RGB HTML/CSS colour string. Note that this will perform a #to_rgb operation using the default conversion formula.
75 76 77 |
# File 'lib/color/cmyk.rb', line 75 def html to_rgb.html 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.
63 64 65 |
# File 'lib/color/cmyk.rb', line 63 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.
69 70 71 |
# File 'lib/color/cmyk.rb', line 69 def pdf_stroke PDF_FORMAT_STR % [ @c, @m, @y, @k, "K" ] end |
#to_cmyk ⇒ Object
146 147 148 |
# File 'lib/color/cmyk.rb', line 146 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).
137 138 139 140 141 142 143 |
# File 'lib/color/cmyk.rb', line 137 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_hsl ⇒ Object
Converts to RGB then HSL.
156 157 158 |
# File 'lib/color/cmyk.rb', line 156 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 in color-tools 1.2 or later. The Adobe method is not used by default; to enable it, pass true
to #to_rgb.
Future versions of color-tools may offer other conversion mechanisms that offer greater colour fidelity.
113 114 115 116 117 118 119 120 121 122 123 124 |
# File 'lib/color/cmyk.rb', line 113 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 Color::RGB.from_fraction(r, g, b) end |
#to_yiq ⇒ Object
Converts to RGB then YIQ.
151 152 153 |
# File 'lib/color/cmyk.rb', line 151 def to_yiq to_rgb.to_yiq end |