CHAPTER 4
340
Graphics
TABLE 4.39 Additional entries specific to an image dictionary
KEY
TYPE
VALUE
Type
name
name
integer
integer
name or
array
(Optional)
The type of PDF object that this dictionary describes; if
present, must be
XObject
for an image XObject.
(Required)
The type of XObject that this dictionary describes; must be
Image
for an image XObject.
(Required)
The width of the image, in samples.
(Required)
The height of the image, in samples.
(Required for images, except those that use the
JPXDecode
filter; not allowed
for image masks)
The color space in which image samples are specified; it
can be any type of color space except
Pattern
.
If the image uses the
JPXDecode
filter, this entry is optional:
Subtype
Width
Height
ColorSpace
•
If
ColorSpace
is present, any color space specifications in the JPEG2000
data are ignored.
•
If
ColorSpace
is absent, the color space specifications in the JPEG2000
data are used. The
Decode
array is also ignored unless
ImageMask
is
true
.
BitsPerComponent
integer
(Required except for image masks and images that use the
JPXDecode
filter)
The number of bits used to represent each color component. Only a single
value may be specified; the number of bits is the same for all color compo-
nents. Valid values are 1, 2, 4, 8, and (in PDF 1.5) 16. If
ImageMask
is
true
,
this entry is optional, and if specified, its value must be 1.
If the image stream uses a filter, the value of
BitsPerComponent
must be
consistent with the size of the data samples that the filter delivers. In par-
ticular, a
CCITTFaxDecode
or
JBIG2Decode
filter always delivers 1-bit sam-
ples, a
RunLengthDecode
or
DCTDecode
filter delivers 8-bit samples, and
an
LZWDecode
or
FlateDecode
filter delivers samples of a specified size if
a predictor function is used.
If the image stream uses the
JPXDecode
filter, this entry is optional and ig-
nored if present. The bit depth is determined in the process of decoding
the JPEG2000 image.
Intent
name
(Optional; PDF 1.1)
The name of a color rendering intent to be used in
rendering the image (see “Rendering Intents” on page 260). Default value:
the current rendering intent in the graphics state.