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     SECTION 6.2                                  Conversions among Device Color Spaces



6.2.1 Conversion between DeviceGray and DeviceRGB

     Black, white, and intermediate shades of gray can be considered special cases of
     RGB color. A grayscale value is described by a single number: 0.0 corresponds to
     black, 1.0 to white, and intermediate values to different gray levels.

     A gray level is equivalent to an RGB value with all three components the same. In
     other words, the RGB color value equivalent to a specific gray value is simply
        red = gray
      green = gray
       blue = gray

     The gray value for a given RGB value is computed according to the NTSC video
     standard, which determines how a color television signal is rendered on a black-
     and-white television set:
      gray = 0.3 × red + 0.59 × green + 0.11 × blue

6.2.2 Conversion between DeviceGray and DeviceCMYK

     Nominally, a gray level is the complement of the black component of CMYK.
     Therefore, the CMYK color value equivalent to a specific gray level is simply
         cyan   =   0.0
      magenta   =   0.0
       yellow   =   0.0
        black   =   1.0 – gray

     To obtain the equivalent gray level for a given CMYK value, the contributions of
     all components must be taken into account:
                        ·
      gray = 1.0 – min(1.0, 0.3 × cyan + 0.59 × magenta + 0.11 × yellow + black )

     The interactions between the black component and the other three are elaborated
     below.


6.2.3 Conversion from DeviceRGB to DeviceCMYK

     Conversion of a color value from RGB to CMYK is a two-step process. The first
     step is to convert the red-green-blue value to equivalent cyan, magenta, and yel-

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