Add scripts to color-reduce pictures with constraints

Scripts for various Thomson machines, Oric and ZX. All the hard work of
Samuel Devulder, with extensive research on color palette reduction
algorithms, lots of testing, research and debugging.

Thanks a lot!

share/grafx2/scripts/samples_2.4/picture/thomson/lib/bayer.lua

@@ -0,0 +1,68 @@
+-- bayer.lua : bayer matrix suppport.
+--
+-- Version: 02-jan-2017
+--
+-- Copyright 2016-2017 by Samuel Devulder
+--
+-- This program is free software; you can redistribute
+-- it and/or modify it under the terms of the GNU
+-- General Public License as published by the Free
+-- Software Foundation; version 2 of the License.
+-- See <http://www.gnu.org/licenses/>
+
+if not bayer then
+	bayer = {}
+
+	-- doubles a matrix rows and columns
+	function bayer.double(matrix)
+		local m,n=#matrix,#matrix[1]
+		local r = {}
+		for j=1,m*2 do
+			local t = {}
+			for i=1,n*2 do t[i]=0; end
+			r[j] = t;
+		end
+		
+		-- 0 3
+		-- 2 1
+		for j=1,m do
+			for i=1,n do
+				local v = 4*matrix[j][i]
+				r[m*0+j][n*0+i] = v-3
+				r[m*1+j][n*1+i] = v-2
+				r[m*1+j][n*0+i] = v-1
+				r[m*0+j][n*1+i] = v-0
+			end
+		end
+		
+		return r;
+	end
+
+	-- returns a version of the matrix normalized into  
+	-- the 0-1 range
+	function bayer.norm(matrix)
+		local m,n=#matrix,#matrix[1]
+		local max,ret = 0,{}
+		for j=1,m do
+			for i=1,n do
+				max = math.max(max,matrix[j][i])
+			end
+		end
+		-- max=max+1
+		for j=1,m do
+			ret[j] = {}
+			for i=1,n do
+				ret[j][i]=matrix[j][i]/max
+			end
+		end
+		return ret
+	end
+
+	-- returns a normalized order-n bayer matrix
+	function bayer.make(n)
+		local m = {{1}}
+		while n>1 do n,m = n/2,bayer.double(m) end
+		return bayer.norm(m)
+	end
+
+end -- Bayer