Xref: utzoo comp.graphics:3937 comp.windows.x:6833
Path: utzoo!utgpu!watmath!watcgl!ksbooth
From: ksbooth@watcgl.waterloo.edu (Kelly Booth)
Newsgroups: comp.graphics,comp.windows.x
Subject: Re: Luminance from RGB
Message-ID: <7425@
In article <16960@onfcanim.UUCP> dave@onfcanim.UUCP (Dave Martindale) writes:
>For shift/add to be faster than table lookup...

Actually, some solutions combine BOTH techniques.  If the table has two
or more indices (not the case here), then the lookup requires combining
those indices into a single index into the table.  Some compilers do
this with adds and multiplies.  If machine code is written (or if the
compiler is smart) shifts and adds can be substituted.  This may
require that the table size(s) be adjusted to the next larger powers of
two.

Or, recursively, the composite indices can themselves be computed using
a table lookup scheme.