commit 4be126289d7e1e0b4f77c75274a522d10a735e2a
author Debargha Mukherjee <debargha@google.com> Wed Feb 15 21:38:02 2017 -0800
committer Debargha Mukherjee <debargha@google.com> Fri Feb 17 22:16:14 2017 +0000
tree 2216596f6296aa0669df31483917500c8fc75087
parent 5dfa9300840a481a3f35fb9ad50e2b4ac83a6dea

Replace division in self-guided filter

Replaces division with multiplication in self-guided
filter.

The guided filter requires computation of:
n^2.s^2/(n^2.s^2 + n^2.e).
This is now implemented by computation of n^2.s^2/n^2.e followed
by using a lookup table for the function f(x) = x/(x+1).
To compute n^2.s^2/n^2.e, we use an integer multiplication based
implementation which becomes feasible since n^2.e can only
take a few values and their corresponding multipliers can be
pre-computed.
There is also another divison by n, that is also integerized.

Change-Id: Id7b81bbafead0b8f04a1853ec69b9dec423bb66a