[Raku PDF Project] / [PDF-Class Module]
An image dictionary—that is, the dictionary portion of a stream representing an image XObject—may contain the entries listed in Table 89 in addition to the usual entries common to all streams (see Table 5). There are many relationships among these entries, and the current colour space may limit the choices for some of them. Attempting to use an image dictionary whose entries are inconsistent with each other or with the current colour space shall cause an error. The entries described here are appropriate for a base image—one that is an PDF::XObject::Image invoked directly with the Do operator.
Some of the entries are not applicable to images used in other ways, such as for alternate images (see 18.104.22.168, “Alternate Images”), image masks (see 8.9.6, “Masked Images”), or thumbnail images (see 12.3.4, “Thumbnail Images”). Except as noted, such irrelevant entries are simply ignored by a conforming reader