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    CHAPTER 6                                                                  Rendering



6.2 Conversions among Device Color Spaces

    Each raster output device has a native color space, which typically is one of the
    standard device color spaces (DeviceGray, DeviceRGB, or DeviceCMYK). In other
    words, most devices support reproduction of colors according to a grayscale
    (monochrome), RGB (red-green-blue), or CMYK (cyan-magenta-yellow-black)
    model. If the device supports continuous-tone output, reproduction occurs di-
    rectly. Otherwise, it is accomplished by means of halftoning.

    A device’s native color space is also called its process color model. Process colors
    are ones that are produced by combinations of one or more standard process
    colorants. Colors specified in any device or CIE-based color space are rendered as
    process colors. (A device can also support additional spot colorants, which can be
    painted only by means of Separation or DeviceN color spaces. They are not in-
    volved in the rendering of device or CIE-based color spaces, nor are they subject
    to the conversions described below.)

    Note: Some devices provide a native color space that is not one of the three named
    above but consists of a different combination of colorants. In that case, conversion
    from the standard device color spaces to the device’s native color space is performed
    by device-dependent means.

    Knowing the native color space and other output capabilities of the device, the
    consumer application can automatically convert the color values specified in a
    document to those appropriate for the device’s native color space. For example, if
    a document specifies colors in the DeviceRGB color space but the device supports
    grayscale (such as a monochrome display) or CMYK (such as a color printer), the
    consumer application performs the necessary conversions. If the document spec-
    ifies colors directly in the device’s native color space, no conversions are neces-
    sary.

    The algorithms used to convert among device color spaces are very simple. As
    perceived by a human viewer, the conversions produce only crude approxima-
    tions of the original colors. More sophisticated control over color conversion can
    be achieved by means of CIE-based color specification and rendering. Addition-
    ally, device color spaces can be remapped into CIE-based color spaces (see
    “Default Color Spaces” on page 257).

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