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SECTION 4.5                                                                Color Spaces



instance, painting tints of the Red component on a white background produces a
result that varies from white to cyan.
Note that this exception applies only to colorants for additive devices, not to the spe-
cific names Red, Green, and Blue. In contrast, a printer might have a (subtractive)
ink named, for example, Red, which should work as a Separation color space just
the same as any other supported colorant.

If the colorant name associated with a Separation color space does not cor-
respond to a colorant available on the device, the application arranges for subse-
quent painting operations to be performed in an alternate color space. The
intended colors can be approximated by colors in a device or CIE-based color
space, which are then rendered with the usual primary or process colorants:

• The alternateSpace parameter must be an array or name object that identifies
  the alternate color space, which can be any device or CIE-based color space but
  not another special color space (Pattern, Indexed, Separation, or DeviceN).
• The tintTransform parameter must be a function (see Section 3.9, “Functions”).
  During subsequent painting operations, an application calls this function to
  transform a tint value into color component values in the alternate color space.
  The function is called with the tint value and must return the corresponding
  color component values. That is, the number of components and the interpre-
  tation of their values depend on the alternate color space.

Note: Painting in the alternate color space may produce a good approximation of
the intended color when only opaque objects are painted. However, it does not cor-
rectly represent the interactions between an object and its backdrop when the object
is painted with transparency or when overprinting (see Section 4.5.6, “Overprint
Control”) is enabled.

Example 4.11 illustrates the specification of a Separation color space (object 5)
that is intended to produce a color named LogoGreen. If the output device has no
colorant corresponding to this color, DeviceCMYK is used as the alternate color
space, and the tint transformation function (object 12) maps tint values linearly
into shades of a CMYK color value approximating the LogoGreen color.

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