8-bit vs 16-bit Precision, and Indexing

[rich2005]

Quote:...snip..what I'm getting is that unless there's MORE than the 16 million color limit in the original 16-bit image, then converting it into 8-bit won't change much.

It depends on where you get that 16-bit image.
If you want a better estimate of the number of (unique) colours in an image then use ImageMagick identify

Code:

identify -format "UniqueColors: %k\n" image.ext

As an example: The same RAW image (12 bit ?)  imported (using nufraw) into Gimp. First as 8 bit and exported as an 8 bit tif.
Then a separate import as 16 bit into Gimp, exported as 16 bit tif.

   

Then export format. A jpeg is 8 bit but worth editing as 16 bit to avoid effects such as ramping. When exported it is back to 8 bit and file size determined by the jpeg quality setting.  
Those tiff images above and the 16 bit is obviously much bigger than the 8 bit even with compression. 130 MB versus 44 MB.