CHAPTER 4
302
Graphics
4.6.3 Shading Patterns
Shading patterns (PDF 1.3)
provide a smooth transition between colors across an
area to be painted, independent of the resolution of any particular output device
and without specifying the number of steps in the color transition. Patterns of
this type are described by pattern dictionaries with a pattern type of 2. Table 4.26
shows the contents of this type of dictionary.
TABLE 4.26 Entries in a type 2 pattern dictionary
KEY
TYPE
VALUE
Type
name
integer
dictionary
or stream
array
(Optional)
The type of PDF object that this dictionary describes; if present,
must be
Pattern
for a pattern dictionary.
(Required)
A code identifying the type of pattern that this dictionary de-
scribes; must be 2 for a shading pattern.
(Required)
A shading object (see below) defining the shading pattern’s gradi-
ent fill. The contents of the dictionary consist of the entries in Table 4.28 and
those in one of Tables 4.29 to 4.34.
(Optional)
An array of six numbers specifying the pattern matrix (see Section
[ 1 0 0 1 0 0 ]
.
(Optional)
A graphics state parameter dictionary (see Section 4.3.4, “Graph-
put into effect temporarily while the shading pattern is painted. Any parame-
ters that are not so specified are inherited from the graphics state that was in
effect at the beginning of the content stream in which the pattern is defined
as a resource.
PatternType
Shading
Matrix
ExtGState
dictionary
The most significant entry is
Shading
, whose value is a
shading object
defining
the properties of the shading pattern’s
gradient fill.
This is a complex “paint” that
determines the type of color transition the shading pattern produces when paint-
ed across an area. A shading object may be a dictionary or a stream, depending
on the type of shading; the term
shading dictionary
is used generically throughout
this section to refer to either a dictionary object or the dictionary portion of a
stream object. (Those shading objects that are streams are specifically identified
as such in the descriptions of particular shading types; unless otherwise stated,
they are understood to be simple dictionaries instead.)