SECTION 4.5
267
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
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.