CHAPTER 3
74
Syntax
samples (a process called
differencing),
and encoding the differences rather than
the raw sample values, can reduce the size of the output data. Furthermore, when
the image data contains several color components (red-green-blue or cyan-
magenta-yellow-black) per sample, taking the difference between the values of
corresponding components in adjacent samples, rather than between different
color components in the same sample, often reduces the output data size.
LZWDecode
and
FlateDecode
filters. Except where otherwise noted, all values supplied to the
decoding filter for any optional parameters must match those used when the data
was encoded.
TABLE 3.7 Optional parameters for LZWDecode and FlateDecode filters
KEY
TYPE
VALUE
Predictor
integer
A code that selects the predictor algorithm, if any. If the value of this entry
is 1, the filter assumes that the normal algorithm was used to encode the data,
without prediction. If the value is greater than 1, the filter assumes that the
data was differenced before being encoded, and
Predictor
selects the predic-
tor algorithm. For more information regarding
Predictor
values greater
than 1, see “LZW and Flate Predictor Functions,” below. Default value: 1.
(Used only if
Predictor
is greater than 1)
The number of interleaved color com-
ponents per sample. Valid values are 1 to 4 in PDF 1.2 or earlier and 1 or
greater in PDF 1.3 or later. Default value: 1.
(Used only if
Predictor
is greater than 1)
The number of bits used to represent
each color component in a sample. Valid values are 1, 2, 4, 8, and (in PDF 1.5)
16. Default value: 8.
(Used only if
Predictor
is greater than 1)
The number of samples in each row.
Default value: 1.
(
LZWDecode
only)
An indication of when to increase the code length. If the
value of this entry is 0, code length increases are postponed as long as pos-
sible. If the value is 1, code length increases occur one code early. This pa-
rameter is included because LZW sample code distributed by some vendors
increases the code length one code earlier than necessary. Default value: 1.
Colors
integer
BitsPerComponent
integer
Columns
integer
integer
EarlyChange