CHAPTER 7
534
Transparency
stack and replaced by the group object, numbered
i,
followed by the remaining
objects to be painted on top of the group, renumbered starting at
i
+
1. This oper-
ation applies recursively to any nested subgroups. Henceforth, the term
element
(denoted
E
i
) refers to a member of some group; it can be either an individual ob-
ject or a contained subgroup.
From the perspective of a particular element in a nested group, there are three
different backdrops of interest:
The group backdrop
is the result of compositing all elements up to but not in-
cluding the first element in the group. (This definition is altered if the parent
group is a knockout group; see Section 7.3.5, “Knockout Groups.”)
The initial backdrop
is a backdrop that is selected for compositing the group’s
first element. This is either the same as the group backdrop (for a non-isolated
group) or a fully transparent backdrop (for an isolated group).
The immediate backdrop
is the result of compositing all elements in the group
up to but not including the current element.
When all elements in a group have been composited, the result is treated as if the
group were a single object, which is then composited with the group backdrop.
(This operation occurs whether the initial backdrop chosen for compositing the
elements of the group was the group backdrop or a transparent backdrop. There
is a special correction to ensure that the backdrop’s contribution to the overall re-
sult is applied only once.)
7.3.3 Group Compositing Computations
The color and opacity of a group are defined by the
group compositing function:
C
,
f
,
α
=
Composite
(
C
0
,
α
0
,
G
)
where the variables have the meanings shown in Table 7.7.
TABLE 7.7 Arguments and results of the group compositing function
VARIABLE
MEANING
G
The transparency group: a compound object consisting of all ele-
ments
E
1
, … ,
E
n
of the group—the
n
constituent objects’ colors,
shapes, opacities, and blend modes
Index Bookmark Pages Text
Previous Next
Pages: Index All Pages
This HTML file was created by VeryPDF PDF to HTML Converter product.