diff --git a/day20/part1.lua b/day20/part1.lua
new file mode 100755
index 0000000..02ed006
--- /dev/null
+++ b/day20/part1.lua
@@ -0,0 +1,64 @@
+#!/usr/bin/env luajit
+require("utils")
+require("grid")
+
+local f = io.open(arg[3])
+local line = f:read("*l")
+local enhancer = {}
+for char in chars(line) do
+	if char == "#" then
+		table.insert(enhancer, 1)
+	else
+		table.insert(enhancer, 0)
+	end
+end
+f:read("*l")
+line = f:read("*l")
+local image = grid(1, 1, #line, #line, 0)
+local r, c = 0, 0
+while line ~= nil do
+	r = r + 1
+	c = 0
+	for char in chars(line) do
+		c = c + 1
+		if char == "#" then
+			image:set(r, c, 1)
+		end
+	end
+	line = f:read("*l")
+end
+
+function zoom(image, enhancer)
+	local newdefault = enhancer[image.default * (#enhancer - 1) + 1]
+	local newimage = grid(image.top - 1, image.left - 1,
+		image.height + 2, image.width + 2, newdefault)
+	for v, r, c in image:iter() do
+		newimage:set(r, c, v)
+	end
+	return newimage
+end
+
+function enhance(image, enhancer)
+	local newimage = zoom(image, enhancer)
+	for _, r, c in newimage:iter() do
+		local index = 0
+		for v, _, _ in image:neigh9(r, c) do
+			index = index * 2 + v
+		end
+		newimage:set(r, c, enhancer[index + 1])
+	end
+	return newimage
+end
+
+local function pprint(c)
+	if c == 0
+	then return "."
+	else return "#"
+	end
+end
+
+local counter = 0
+for v in enhance(enhance(image, enhancer), enhancer):iter() do
+	counter = counter + v
+end
+print(counter)
diff --git a/day20/part2.lua b/day20/part2.lua
new file mode 100755
index 0000000..3f7e24d
--- /dev/null
+++ b/day20/part2.lua
@@ -0,0 +1,68 @@
+#!/usr/bin/env luajit
+require("utils")
+require("grid")
+
+local f = io.open(arg[3])
+local line = f:read("*l")
+local enhancer = {}
+for char in chars(line) do
+	if char == "#" then
+		table.insert(enhancer, 1)
+	else
+		table.insert(enhancer, 0)
+	end
+end
+f:read("*l")
+line = f:read("*l")
+local image = grid(1, 1, #line, #line, 0)
+local r, c = 0, 0
+while line ~= nil do
+	r = r + 1
+	c = 0
+	for char in chars(line) do
+		c = c + 1
+		if char == "#" then
+			image:set(r, c, 1)
+		end
+	end
+	line = f:read("*l")
+end
+
+function zoom(image, enhancer)
+	local newdefault = enhancer[image.default * (#enhancer - 1) + 1]
+	local newimage = grid(image.top - 1, image.left - 1,
+		image.height + 2, image.width + 2, newdefault)
+	for v, r, c in image:iter() do
+		newimage:set(r, c, v)
+	end
+	return newimage
+end
+
+function enhance(image, enhancer)
+	local newimage = zoom(image, enhancer)
+	for _, r, c in newimage:iter() do
+		local index = 0
+		for v, _, _ in image:neigh9(r, c) do
+			index = index * 2 + v
+		end
+		newimage:set(r, c, enhancer[index + 1])
+	end
+	return newimage
+end
+
+local function pprint(c)
+	if c == 0
+	then return "."
+	else return "#"
+	end
+end
+
+for i = 1, 50 do
+	image = enhance(image, enhancer)
+end
+
+local counter = 0
+for v in image:iter() do
+	counter = counter + v
+end
+print(counter)
diff --git a/grid.lua b/grid.lua
new file mode 100644
index 0000000..4eaeb61
--- /dev/null
+++ b/grid.lua
@@ -0,0 +1,83 @@
+local function set(self, r, c, v)
+	if r < self.top or r > self.bottom or c < self.left or c > self.right then
+		error(string.format("index (%d %d) out of bounds (%d..%d %d..%d)",
+		                    r, c, self.top, self.bottom, self.left, self.right))
+	end
+	self.grid[r * self.width + c] = v
+end
+
+local function get(self, r, c)
+	if r < self.top or r > self.bottom or c < self.left or c > self.right then
+		if self.default then
+			return self.default
+		else
+			error(string.format("index (%d %d) out of bounds (%d..%d %d..%d)",
+			                    r, c, self.top, self.bottom, self.left, self.right))
+		end
+	end
+	local item = self.grid[r * self.width + c]
+	if item == nil and self.default then
+		return self.default
+	else
+		return item
+	end
+end
+
+local function iter(self, r, c, h, w)
+	if r == nil then r = self.top end
+	if c == nil then c = self.left end
+	if h == nil then h = self.height end
+	if w == nil then w = self.width end
+	local r0, c0 = r, c
+	return function()
+		if r0 > r + h - 1 then return nil end
+		local rb, cb = r0, c0
+		c0 = c0 + 1
+		if c0 > c + w - 1 then
+			c0 = c
+			r0 = r0 + 1
+		end
+		return self:get(rb, cb), rb, cb
+	end
+end
+
+local function neigh9(self, r, c, exclude)
+	local iter = self:iter(r - 1, c - 1, 3, 3)
+	return function()
+		local i, ri, ci = iter()
+		if exclude and ri == r and ci == c then
+			local i, ri, ci = iter()
+		end
+		return i, ri, ci
+	end
+end
+
+local function write(self, format)
+	if not format then format = function(i)
+		return string.format("%3s", i)
+	end end
+	for r = self.top, self.bottom do
+		for c = self.left, self.right do
+			io.write(format(self:get(r, c)))
+		end
+		io.write("\n")
+	end
+end
+
+function grid(top, left, width, height, default)
+	return {
+		top = top,
+		left = left,
+		height = height,
+		width = width,
+		bottom = top + height - 1,
+		right = left + width - 1,
+		default = default,
+		grid = {},
+		get = get,
+		set = set,
+		iter = iter,
+		neigh9 = neigh9,
+		write = write,
+	}
+end