External Palette Chunk

Instead of a PLT chunk, an RDIB may contain an XPLT chunk, which indicates that the bitmap's palette is stored outside the bitmap. The palette might be stored in a separate file or as a separate compound file element. The XPLT chunk indicates the name and location of the external palette chunk and is defined as follows:

<XPLT-chunk>  XPLT(<fccLocation:FOURCC> <szPaletteName::ZSTR>)

The fccLocation contains one of the following FOURCC values specifying the location of the external chunk:

fccLocation Value

Chunk Location
'full'
Palette is located in an external file, and the szPaletteName value specifies a complete file name with path.
'file'
Palette is located in an external file, and the szPaletteName value specifies a file name without path.
'elem'
Palette is located in the same compound file containing the DIB. The szPaletteName value specifies the name of the compound file element.

The szPaletteName consists of a null-terminated string (ZSTR) containing the name of the external chunk containing the palette.

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