Syntax

   @GenerateRasterPalettes([REJECTABLE], <palette key interpretation> 
      [,<max num palette entries>]) 
      
Arguments

   REJECTABLE

      Specifies if the function will supply a rejection code and message
      to the invalid feature and output it to the rejected port, or will
      fail upon being supplied invalid features.

      A feature can be rejected for the following reasons:
         - The feature has invalid geometry
         - The raster has incompatible bands for palette-generation

   <palette key interpretation>  
   
      The desired key interpretation for the new palette, including data type 
      and bit depth. UINT8 has at most 256 palette entries. UINT16 has at most 
      65,536 palette entries. UINT32 has at most 4,294,967,296 palette entries.
   
      Range: UINT8 | UINT16 | UINT32 
      
   <max num palette entries>   
   
      The actual number of entries in the new palette. The palette key 
      interpretation may allow more entries in the palette, but this number sets 
      the maximum number of entries to be generated. The minimum number is 1. 
      This number cannot exceed the maximum number of entries in the palette key 
      interpretation.

      Range: positive integers 
      
Description

   The @GenerateRasterPalettes function is used to generate a palette from a 
   raster without a palette. This function removes the selected band(s) from a 
   raster and produces a new band and a new palette. The function replaces the 
   values on the selected band(s) by the palette keys on the new band and the 
   values on the new palette. This process often greatly reduce the size of the 
   output raster. This also implies that the output raster has only as many 
   different colors as the new palette. When the input raster has more different 
   colors than the specified number of colors in the function parameter, the 
   color reduction mechanism in the function will merge similar colors to make 
   sure that the maximum number of colors in the palette will not exceed the 
   specified number in the parameter.

   Since this function can be used to generate a palette from a raster without a 
   palette, translations from raster formats that do not produce a palette, to 
   raster formats that require a palette are possible now. For example, when a 
   raster writer, such as the GIFRASTER and the PNGRASTER, requires a palette, 
   this function can be used to generate a palette from the source raster, such 
   as the JPEG and the ECW, which does not have a palette. 

   In details, the selected band(s) of the input raster will be replaced by a 
   new band with the specified palette key interpretation. This new band will 
   have a new palette. The interpretations of the selected band(s) determine the 
   value interpretation of the palette. For example, if the interpretations of 
   the selected bands are RED8, GREEN8, and BLUE8, the value interpretation of 
   the new palette will be RGB24. The specified maximum number of palette 
   entries determines the maximum number of palette entries to be generated in 
   the new palette. This number is useful in some situations. For example, XPM 
   can write at most 87 entries in a palette, whereas GeoTIFF can write at most 
   2,147,483,648 entries. To standardize the number of entries and the color in 
   the palettes being written to both formats, the @GenerateRasterPalettes 
   function can be used by setting the key interpretation to UINT8 and the 
   maximum number of palette entries to 87 before passing the raster feature to 
   the writers of both formats.

   This operation is lossy. The maximum number of entries determines the quality 
   of the output raster. More number of entries implies higher quality.

   The two arguments allow the function to generate a palette that can contain 
   more entries than the actual number of entries to be generated. However, the 
   specified maximum number of entries must not be larger than the number of 
   entries of the specified key interpretation.

   The selected band(s) determines the value interpretation of the palette. 
   Therefore, the selected band(s) must be in the correct order in the raster, 
   and the interpretations of the selected band(s) must be a meaningful palette 
   value interpretation that FME currently supports. A bad example would be that 
   the selected bands are RED8, GREEN16, and BLUE8 in order. Another bad example 
   would be that the selected bands are GREEN8, BLUE8, and RED8 in order. 
   Furthermore, the selected band(s) cannot have any palettes. Please note that 
   if the selected bands are all UINT8 but the intended palette value 
   interpretation is RGB24, the selected bands must be reinterpreted first.

   This function supports sub-selection of raster bands.