README

Simple* bilateral filter
========================

Copyright (C) 2010 David Beynon <dave@spectral3d.co.uk.org>

Based on gimp plugin framework (C) 2000-2003  Michael Natterer <mitch@gimp.org>

This package implements a fast "surface blur" effect based on a simplified
bilateral filter.  Results are similar to those of "Selective Gaussian Blur",
but performance should be substantially better for large filter sizes.

The main features are as follows:

- O(1) filtering algorithm makes performance almost independent of filter 
  radius.

To build and install it, just ...

	./configure
	make
	make install

Technical stuff:

The O(1) filtering algorithm is based on a structure called the "integral 
histogram".  This allows extremely rapid extraction of histograms for 
rectangular regions of an image, at the cost of absurd amounts of memory.  In
order to keep the memory usage under control the filter works on the image in
tiles, and at a reduced precision.  These are currently set to give an overhead
of 64mb.

Image quality may be improved by increasing the number of bins in use, and
performance by increasing the size of tiles.  These may be adjusted by editing
"settings.h".

Quality and performance controls may be added to future versions.

The word "simple" refers to the mathematical characteristics of the spatial 
filter kernel.  Hopefully the code is fairly simple to read, but bits of it
were quite fiddly :)