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/none_to8.lua

@@ -0,0 +1,82 @@
+-- ostro_to8.lua : convert a color image to a BM16
+-- (160x200x16) thomson image using the Ostromoukhov's
+-- error diffusion algorithm.
+--
+-- 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/>
+
+run('lib/thomson.lua')
+run('lib/ostromoukhov.lua')
+run('lib/color_reduction.lua')
+-- run('lib/zzz.lua')
+	
+-- get screen size
+local screen_w, screen_h = getpicturesize()
+
+-- Converts thomson coordinates (0-159,0-199) into screen coordinates
+local function thom2screen(x,y)
+	local i,j;
+	if screen_w/screen_h < 1.6 then
+		i = x*screen_h/200
+		j = y*screen_h/200
+	else
+		i = x*screen_w/320
+		j = y*screen_w/320
+	end
+	return math.floor(i*2), math.floor(j)
+end
+
+-- return the Color @(x,y) in normalized linear space (0-1)
+-- corresonding to the thomson screen (x in 0-319, y in 0-199)
+local function getLinearPixel(x,y)
+	local x1,y1 = thom2screen(x,y)
+	local x2,y2 = thom2screen(x+1,y+1)
+	if x2==x1 then x2=x1+1 end
+	if y2==y1 then y2=y1+1 end
+
+	local p = Color:new(0,0,0);
+	for j=y1,y2-1 do
+		for i=x1,x2-1 do
+			p:add(getLinearPictureColor(i,j))
+		end
+	end
+	p:div((y2-y1)*(x2-x1)) --:floor()
+	
+	return p
+end
+
+local red = ColorReducer:new():analyzeWithDither(160,200,
+	getLinearPixel,
+    function(y)
+		thomson.info("Collecting stats...",math.floor(y/2),"%")
+	end)
+	
+-- BM16 mode
+thomson.setBM16()
+
+-- define palette
+local palette = red:boostBorderColors():buildPalette(16)
+thomson.palette(0, palette)
+
+-- convert picture
+OstroDither:new(palette, 0)
+           :dither(thomson.h,thomson.w,
+             function(y,x) return getLinearPixel(x,y) end,
+			 function(y,x,c) thomson.pset(x,y,c) end, 
+			 true,
+			 function(x) thomson.info("Converting...",math.floor(x*100/160),"%") end)
+
+-- refresh screen
+setpicturesize(320,200)
+thomson.updatescreen()
+finalizepicture()
+
+-- save picture
+thomson.savep()