SECTION 3.3
89
Filters
When using the
JPXDecode
filter with image XObjects, there are changes to and
constraints on some entries in the image dictionary (see Section 4.8.4, “Image
•
Width
and
Height
must match the corresponding width and height values in
the JPEG2000 data.
•
ColorSpace
is optional since JPEG2000 data contain color space specifications.
If present, it determines how the image samples are interpreted, and the color
space specifications in the JPEG2000 data are ignored. The number of color
channels in the JPEG2000 data must match the number of components in the
color space; the PDF producer must ensure that the samples are consistent with
the color space used.
Any color space other than
Pattern
may be specified. If an
Indexed
color space
is used, it is subject to the PDF limit of 256 colors. (The analogous concept in
the JPEG2000 color specifications is a
palette color space,
which has a limit of
1024 colors.) If the color space does not match one of JPX’s enumerated color
spaces (for example, if it has two color components or more than four), it can
be specified as a vendor color space in the JPX data.
If
ColorSpace
is not present in the image dictionary, the color space informa-
tion in the JPEG2000 data is used. Consumer applications must support the
JPX baseline set of enumerated color spaces; they are also responsible for deal-
ing with the interaction between the color spaces and the bit depth of samples.
If multiple color space specifications are given in the JPEG2000 data, a render-
ing application should attempt to use the one with the highest precedence and
best approximation value. If the color space is given by an unsupported ICC
profile, the next lower color space, in terms of precedence and approximation
value, is used. If no supported color space is found, the color space used should
be
DeviceGray
,
DeviceRGB
, or
DeviceCMYK
, depending on the number of color
channels in the JPEG2000 data.
•
SMaskInData
specifies whether soft-mask information packaged with the im-
age samples should be used (see “Soft-Mask Images” on page 553); if it is, the
SMask
entry is not needed. If
SMaskInData
is nonzero, there must be only one
opacity channel in the JPEG2000 data and it must apply to all color channels.
•
Decode
is ignored, except in the case where the image is treated as a mask; that
is, when
ImageMask
is true. In this case, the JPEG2000 data must provide a sin-
gle color channel with 1-bit samples.