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SECTION 3.3                                                                 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
Dictionaries” for details on these entries):
• 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.

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