CHAPTER 4
266
Graphics
that can be achieved with the given colorant, and 1.0 is the darkest. (This conven-
tion is the same as for
DeviceCMYK
color components but opposite to the one for
DeviceGray
and
DeviceRGB
.) The initial value for both the stroking and non-
stroking color in the graphics state is 1.0. The
SCN
and
scn
operators respectively
set the current stroking and nonstroking color to a tint value. A sampled image
with single-component samples can also be used as a source of tint values.
The
name
parameter is a name object specifying the name of the colorant that
this
Separation
color space is intended to represent (or one of the special names
All
or
None
; see below). Such colorant names are arbitrary, and there can be any
number of them, subject to implementation limits.
The special colorant name
All
refers collectively to all colorants available on an
output device, including those for the standard process colorants. When a
Separation
space with this colorant name is the current color space, painting
operators apply tint values to all available colorants at once. This is useful for pur-
poses such as painting registration targets in the same place on every separation.
Such marks are typically painted as the last step in composing a page to ensure
that they are not overwritten by subsequent painting operations.
The special colorant name
None
never produces any visible output. Painting op-
erations in a
Separation
space with this colorant name have no effect on the cur-
rent page.
All devices support
Separation
color spaces with the colorant names
All
and
None
, even if they do not support any others.
Separation
spaces with either of
these colorant names ignore the
alternateSpace
and
tintTransform
parameters (dis-
cussed below), although valid values must still be provided.
At the moment the color space is set to a
Separation
space, the consumer applica-
tion determines whether the device has an available colorant corresponding to
the name of the requested space. If so, the application ignores the
alternateSpace
and
tintTransform
parameters; subsequent painting operations within the space
apply the designated colorant directly, according to the tint values supplied.
Note:
The preceding paragraph applies only to subtractive output devices such as
printers and imagesetters. For an additive device such as a computer display, a
Separation
color space never applies a process colorant directly; it always reverts to
the alternate color space as described below. This is because the model of applying
process colorants independently does not work as intended on an additive device; for