Class: Color::CMYK

### Home Classes Methods

### In Files

- lib/color.rb
- lib/color/cmyk.rb

### Parent

Object

### Methods

- ::from_fraction
- ::new
- #==
- #html
- #pdf_fill
- #pdf_stroke
- #to_cmyk
- #to_grayscale
- #to_greyscale
- #to_hsl
- #to_rgb
- #to_yiq

### Files

- Changelog
- Install
- README

### Class/Module Index

Quicksearch

- Color
- Color::CMYK
- Color::CSS
- Color::GrayScale
- Color::GreyScale
- Color::Palette
- Color::Palette::Gimp
- Color::Palette::MonoContrast
- Color::RGB
- Color::RGB::Metallic
- Color::YIQ

No matching classes.

# 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.

### 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.

### Attributes

c[RW]
k[RW]
m[RW]
y[RW]

### Public Class Methods

from_fraction(c = 0, m = 0, y = 0, k = 0) click to toggle source

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

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

    # File lib/color/cmyk.rb, line 41
    def self.from_fraction(c = 0, m = 0, y = 0, k = 0)
      colour = Color::CMYK.new
      colour.c = c
      colour.m = m
      colour.y = y
      colour.k = k
      colour
    end

new(c = 0, m = 0, y = 0, k = 0) click to toggle source

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)

    # 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

### Public Instance Methods

==(other) click to toggle source

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.

    # 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() click to toggle source

Present the colour as an RGB HTML/CSS colour string. Note that this will perform a to_rgb operation using the default conversion formula.

    # File lib/color/cmyk.rb, line 75
    def html
      to_rgb.html
    end

pdf_fill() click to toggle source

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

    # File lib/color/cmyk.rb, line 63
    def pdf_fill
      PDF_FORMAT_STR % [ @c, @m, @y, @k, "k" ]
    end

pdf_stroke() click to toggle source

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

    # File lib/color/cmyk.rb, line 69
    def pdf_stroke
      PDF_FORMAT_STR % [ @c, @m, @y, @k, "K" ]
    end

to_cmyk() click to toggle source

    # File lib/color/cmyk.rb, line 146
    def to_cmyk
      self
    end

to_grayscale() click to toggle source

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).

    # 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

Also aliased as: to_greyscale
to_greyscale() click to toggle source
Alias for: to_grayscale
to_hsl() click to toggle source

Converts to RGB then HSL.

    # File lib/color/cmyk.rb, line 156
    def to_hsl
      to_rgb.to_hsl
    end

to_rgb(use_adobe_method = false) click to toggle source

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.

    # 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() click to toggle source

Converts to RGB then YIQ.

    # File lib/color/cmyk.rb, line 151
    def to_yiq
      to_rgb.to_yiq
    end

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