SECTION 4.9
355
Form XObjects
Example 4.30
q
% Save graphics state
17 0 0 17 298 388 cm
% Scale and translate coordinate space
BI
% Begin inline image object
/W 17
% Width in samples
/H 17
% Height in samples
/CS /RGB
% Color space
/BPC 8
% Bits per component
/F [ /A85 /LZW ]
% Filters
ID
% Begin image data
J1/gKA>.]AN&J?]-<HW]aRVcg*bb.\eKAdVV%/PcZ
… Omitted data …
R.s(4KE3&d&7hb*7[%Ct2HCqC~>
EI
% End inline image object
Q
% Restore graphics state
4.9 Form XObjects
A
form XObject
is a PDF content stream that is a self-contained description of any
sequence of graphics objects (including path objects, text objects, and sampled
images). A form XObject may be painted multiple times—either on several pages
or at several locations on the same page—and produces the same results each
time, subject only to the graphics state at the time it is invoked. Not only is this
shared definition economical to represent in the PDF file, but under suitable cir-
cumstances the PDF consumer application can optimize execution by caching the
results of rendering the form XObject for repeated reuse.
Note:
The term
form
also refers to a completely different kind of object, an
inter-
active form
(sometimes called an
AcroForm),
discussed in Section 8.6, “Interactive
tion of forms in the PostScript language, interactive forms are the PDF equivalent of
the familiar paper instrument. Any unqualified use of the word
form
is understood
to refer to an interactive form; the type of form described here is always referred to
explicitly as a
form XObject.