diff --git a/init.lua b/init.lua
index 1a0bd47..52918be 100644
--- a/init.lua
+++ b/init.lua
@@ -1,5 +1,23 @@
 tga_encoder = {}
 
+tga_encoder.features = {}
+tga_encoder.features.color_format = {
+	["A1R5G5B5"] = true,
+	["B8G8R8"] = true,
+	["B8G8R8A8"] = true,
+	["Y8"] = true,
+}
+tga_encoder.features.colormap = {
+}
+tga_encoder.features.compression = {
+	["RAW"] = true,
+	["RLE"] = true,
+}
+tga_encoder.features.scanline_order = {
+	["bottom_top"] = true,
+	["top_bottom"] = true,
+}
+
 local image = setmetatable({}, {
 	__call = function(self, ...)
 		local t = setmetatable({}, {__index = self})
@@ -58,8 +76,8 @@ function image:encode_image_spec(properties)
 	)
 	local scanline_order = properties.scanline_order
 	assert (
-		"bottom-top" == scanline_order or
-		"top-bottom" == scanline_order
+		"bottom_top" == scanline_order or
+		"top_bottom" == scanline_order
 	)
 	local pixel_depth
 	if 0 ~= #properties.colormap then
@@ -73,16 +91,21 @@ function image:encode_image_spec(properties)
 	local x_origin_hi = 0
 	local y_origin_lo = 0
 	local y_origin_hi = 0
-	local image_descriptor = 0 -- equal to bottom-top scanline order
+	local image_descriptor = 0 -- equal to bottom_top scanline order
 	local width_lo = self.width % 256
 	local width_hi = math.floor(self.width  / 256)
 	local height_lo = self.height % 256
 	local height_hi = math.floor(self.height / 256)
-	if "top-bottom" == scanline_order then
+	if "top_bottom" == scanline_order then
 		image_descriptor = 32
 		y_origin_lo = height_lo
 		y_origin_hi = height_hi
 	end
+	if "A1R5G5B5" == color_format then
+		image_descriptor = image_descriptor + 1 -- 1 bit alpha channel
+	elseif "B8G8R8A8" == color_format then
+		image_descriptor = image_descriptor + 8 -- 8 bit alpha channel
+	end
 	self.data = self.data .. string.char (
 		x_origin_lo, x_origin_hi,
 		y_origin_lo, y_origin_hi,
@@ -112,7 +135,8 @@ function image:encode_colormap(properties)
 		local max_sample_out = math.pow(2, 5) - 1
 		for i = 1,#colormap,1 do
 			local color = colormap[i]
-			local colorword = 32768 +
+			local colorword = 0 +
+				((math.floor((color[4] / max_sample_in) + 0.5)) * 32768) +  -- transparent if alpha < 128
 				((math.floor((color[1] * max_sample_out / max_sample_in) + 0.5)) * 1024) +
 				((math.floor((color[2] * max_sample_out / max_sample_in) + 0.5)) * 32) +
 				((math.floor((color[3] * max_sample_out / max_sample_in) + 0.5)) * 1)
@@ -207,9 +231,17 @@ function image:encode_data(properties)
 			end
 		else
 			if "RAW" == compression then
-				self:encode_data_R8G8B8_as_A1R5G5B5_raw()
+				if 24 == self.pixel_depth then
+					self:encode_data_R8G8B8_as_A1R5G5B5_raw()
+				elseif 32 == self.pixel_depth then
+					self:encode_data_R8G8B8A8_as_A1R5G5B5_raw()
+				end
 			elseif "RLE" == compression then
-				self:encode_data_R8G8B8_as_A1R5G5B5_rle()
+				if 24 == self.pixel_depth then
+					self:encode_data_R8G8B8_as_A1R5G5B5_rle()
+				elseif 32 == self.pixel_depth then
+					self:encode_data_R8G8B8A8_as_A1R5G5B5_rle()
+				end
 			end
 		end
 	elseif "B8G8R8" == color_format then
@@ -284,6 +316,23 @@ end
 
 function image:encode_data_R8G8B8_as_A1R5G5B5_raw()
 	assert(24 == self.pixel_depth)
+	for _, row in ipairs(self.pixels) do
+		for _, pixel in ipairs(row) do
+			pixel[4] = 255
+		end
+	end
+	self.pixel_depth = 32
+	self:encode_data_R8G8B8A8_as_A1R5G5B5_raw()
+	for _, row in ipairs(self.pixels) do
+		for _, pixel in ipairs(row) do
+			pixel[4] = nil
+		end
+	end
+	self.pixel_depth = 24
+end
+
+function image:encode_data_R8G8B8A8_as_A1R5G5B5_raw()
+	assert(32 == self.pixel_depth)
 	local raw_pixels = {}
 	-- Sample depth rescaling is done according to the algorithm presented in:
 	-- <https://www.w3.org/TR/2003/REC-PNG-20031110/#13Sample-depth-rescaling>
@@ -291,7 +340,8 @@ function image:encode_data_R8G8B8_as_A1R5G5B5_raw()
 	local max_sample_out = math.pow(2, 5) - 1
 	for _, row in ipairs(self.pixels) do
 		for _, pixel in ipairs(row) do
-			local colorword = 32768 +
+			local colorword = 0 +
+				((math.floor((pixel[4] / max_sample_in) + 0.5)) * 32768) +  -- transparent if alpha < 128
 				((math.floor((pixel[1] * max_sample_out / max_sample_in) + 0.5)) * 1024) +
 				((math.floor((pixel[2] * max_sample_out / max_sample_in) + 0.5)) * 32) +
 				((math.floor((pixel[3] * max_sample_out / max_sample_in) + 0.5)) * 1)
@@ -304,10 +354,28 @@ end
 
 function image:encode_data_R8G8B8_as_A1R5G5B5_rle()
 	assert(24 == self.pixel_depth)
+	for _, row in ipairs(self.pixels) do
+		for _, pixel in ipairs(row) do
+			pixel[4] = 255
+		end
+	end
+	self.pixel_depth = 32
+	self:encode_data_R8G8B8A8_as_A1R5G5B5_rle()
+	for _, row in ipairs(self.pixels) do
+		for _, pixel in ipairs(row) do
+			pixel[4] = nil
+		end
+	end
+	self.pixel_depth = 24
+end
+
+function image:encode_data_R8G8B8A8_as_A1R5G5B5_rle()
+	assert(32 == self.pixel_depth)
 	local colorword = nil
 	local previous_r = nil
 	local previous_g = nil
 	local previous_b = nil
+	local previous_a = nil
 	local raw_pixel = ''
 	local raw_pixels = {}
 	local count = 1
@@ -320,9 +388,10 @@ function image:encode_data_R8G8B8_as_A1R5G5B5_rle()
 	local max_sample_out = math.pow(2, 5) - 1
 	for _, row in ipairs(self.pixels) do
 		for _, pixel in ipairs(row) do
-			if pixel[1] ~= previous_r or pixel[2] ~= previous_g or pixel[3] ~= previous_b or count == 128 then
+			if pixel[1] ~= previous_r or pixel[2] ~= previous_g or pixel[3] ~= previous_b or pixel[4] ~= previous_a or count == 128 then
 				if nil ~= previous_r then
-					colorword = 32768 +
+					colorword = 0 +
+						((math.floor((previous_a / max_sample_in) + 0.5)) * 32768) +  -- transparent if alpha < 128
 						((math.floor((previous_r * max_sample_out / max_sample_in) + 0.5)) * 1024) +
 						((math.floor((previous_g * max_sample_out / max_sample_in) + 0.5)) * 32) +
 						((math.floor((previous_b * max_sample_out / max_sample_in) + 0.5)) * 1)
@@ -357,12 +426,14 @@ function image:encode_data_R8G8B8_as_A1R5G5B5_rle()
 				previous_r = pixel[1]
 				previous_g = pixel[2]
 				previous_b = pixel[3]
+				previous_a = pixel[4]
 			else
 				count = count + 1
 			end
 		end
 	end
-	colorword = 32768 +
+	colorword = 0 +
+		((math.floor((previous_a / max_sample_in) + 0.5)) * 32768) +  -- transparent if alpha < 128
 		((math.floor((previous_r * max_sample_out / max_sample_in) + 0.5)) * 1024) +
 		((math.floor((previous_g * max_sample_out / max_sample_in) + 0.5)) * 32) +
 		((math.floor((previous_b * max_sample_out / max_sample_in) + 0.5)) * 1)
@@ -585,7 +656,7 @@ function image:encode(properties)
 	local properties = properties or {}
 	properties.colormap = properties.colormap or {}
 	properties.compression = properties.compression or "RAW"
-        properties.scanline_order = properties.scanline_order or "bottom-top"
+        properties.scanline_order = properties.scanline_order or "bottom_top"
 
 	self.pixel_depth = #self.pixels[1][1] * 8
 
diff --git a/tools/generate_test_textures.lua b/tools/generate_test_textures.lua
index 24e4b32..b3e2765 100755
--- a/tools/generate_test_textures.lua
+++ b/tools/generate_test_textures.lua
@@ -5,10 +5,11 @@ local _ = { 0 }
 local R = { 1 }
 local G = { 2 }
 local B = { 3 }
+local W = { 4 }
 
 local pixels_colormapped_bt = {
-	{ _, _, _, _, _, B, _, B, },
-	{ _, _, _, _, _, B, B, B, },
+	{ W, W, _, _, _, B, _, B, },
+	{ W, W, _, _, _, B, B, B, },
 	{ _, _, G, G, G, B, _, B, },
 	{ _, _, G, _, G, B, B, B, },
 	{ _, R, G, _, _, _, _, _, },
@@ -24,59 +25,85 @@ local pixels_colormapped_tb = {
 	{ _, R, G, _, _, _, _, _, },
 	{ _, _, G, _, G, B, B, B, },
 	{ _, _, G, G, G, B, _, B, },
-	{ _, _, _, _, _, B, B, B, },
-	{ _, _, _, _, _, B, _, B, },
+	{ W, W, _, _, _, B, B, B, },
+	{ W, W, _, _, _, B, _, B, },
 }
 
-image_colormapped_bt = tga_encoder.image(pixels_colormapped_bt)
-image_colormapped_tb = tga_encoder.image(pixels_colormapped_tb)
+local pixels_colormapped_by_scanline_order = {
+	["bottom_top"] = pixels_colormapped_bt,
+	["top_bottom"] = pixels_colormapped_tb,
+}
 
-colormap_32bpp = {
-	{    0,   0,   0, 128 },
+local colormap_32bpp = {
+	{    0,   0,   0, 127 },
 	{ 255,    0,   0, 255 },
 	{    0, 255,   0, 255 },
 	{    0,   0, 255, 255 },
+	{ 255,  255, 255, 128 },
 }
-image_colormapped_bt:save(
-	"type1_32bpp_bt.tga",
-	{ colormap = colormap_32bpp, color_format = "B8G8R8A8", scanline_order = "bottom-top" }
-)
-image_colormapped_tb:save(
-	"type1_32bpp_tb.tga",
-	{ colormap = colormap_32bpp, color_format = "B8G8R8A8", scanline_order = "top-bottom" }
-)
-image_colormapped_bt:save(
-	"type1_16bpp_bt.tga",
-	{ colormap = colormap_32bpp, color_format = "A1R5G5B5", scanline_order = "bottom-top" }
-)
-image_colormapped_tb:save(
-	"type1_16bpp_tb.tga",
-	{ colormap = colormap_32bpp, color_format = "A1R5G5B5", scanline_order = "top-bottom" }
-)
 
-colormap_24bpp = {
+local colormap_24bpp = {
 	{    0,   0,   0 },
 	{ 255,    0,   0 },
 	{    0, 255,   0 },
 	{    0,   0, 255 },
+	{ 255,  255, 255 },
 }
-image_colormapped_bt:save(
-	"type1_24bpp_bt.tga",
-	{ colormap = colormap_32bpp, color_format = "B8G8R8", scanline_order = "bottom-top" }
-)
-image_colormapped_tb:save(
-	"type1_24bpp_tb.tga",
-	{ colormap = colormap_32bpp, color_format = "B8G8R8", scanline_order = "top-bottom" }
-)
 
-local _ = {    0,   0,   0, 128 }
+local colormap_16bpp = {
+	{    0,   0,   0,   0 },
+	{ 255,    0,   0, 255 },
+	{    0, 255,   0, 255 },
+	{    0,   0, 255, 255 },
+	{ 255,  255, 255, 255 },
+}
+
+local colormap_by_color_format = {
+	["A1R5G5B5"] = colormap_16bpp,
+	["B8G8R8"]   = colormap_24bpp,
+	["B8G8R8A8"] = colormap_32bpp,
+}
+
+for color_format, _ in pairs(
+	tga_encoder.features.color_format
+) do
+	if ("Y8" ~= color_format) then
+		for scanline_order, _ in pairs(
+			tga_encoder.features.scanline_order
+		) do
+			local filename
+			local pixels
+			filename = "type1" ..
+				'-' .. color_format ..
+				'-' .. scanline_order ..
+				'.tga'
+			pixels = pixels_colormapped_by_scanline_order[
+				scanline_order
+			]
+			local colormap = colormap_by_color_format[
+				color_format
+			]
+			local properties = {
+				colormap = colormap,
+				color_format = color_format,
+				scanline_order = scanline_order,
+			}
+			print(filename)
+			local image = tga_encoder.image(pixels)
+			image:save(filename, properties)
+		end
+	end
+end
+
+local _ = {    0,   0,   0, 127 }
 local R = { 255,    0,   0, 255 }
 local G = {    0, 255,   0, 255 }
 local B = {    0,   0, 255, 255 }
+local W = { 255,  255, 255, 128 }
 
 local pixels_rgba_bt = {
-	{ _, _, _, _, _, B, _, B, },
-	{ _, _, _, _, _, B, B, B, },
+	{ W, W, _, _, _, B, _, B, },
+	{ W, W, _, _, _, B, B, B, },
 	{ _, _, G, G, G, B, _, B, },
 	{ _, _, G, _, G, B, B, B, },
 	{ _, R, G, _, _, _, _, _, },
@@ -92,38 +119,24 @@ local pixels_rgba_tb = {
 	{ _, R, G, _, _, _, _, _, },
 	{ _, _, G, _, G, B, B, B, },
 	{ _, _, G, G, G, B, _, B, },
-	{ _, _, _, _, _, B, B, B, },
-	{ _, _, _, _, _, B, _, B, },
+	{ W, W, _, _, _, B, B, B, },
+	{ W, W, _, _, _, B, _, B, },
 }
 
-image_rgba_bt = tga_encoder.image(pixels_rgba_bt)
-image_rgba_tb = tga_encoder.image(pixels_rgba_tb)
-
-image_rgba_bt:save(
-	"type2_32bpp_bt.tga",
-	{ color_format="B8G8R8A8", compression="RAW", scanline_order = "bottom-top" }
-)
-image_rgba_tb:save(
-	"type2_32bpp_tb.tga",
-	{ color_format="B8G8R8A8", compression="RAW", scanline_order = "top-bottom" }
-)
-image_rgba_bt:save(
-	"type10_32bpp_bt.tga",
-	{ color_format="B8G8R8A8", compression="RLE", scanline_order = "bottom-top" }
-)
-image_rgba_tb:save(
-	"type10_32bpp_tb.tga",
-	{ color_format="B8G8R8A8", compression="RLE", scanline_order = "top-bottom" }
-)
+local pixels_rgba_by_scanline_order = {
+	["bottom_top"] = pixels_rgba_bt,
+	["top_bottom"] = pixels_rgba_tb,
+}
 
 local _ = {    0,   0,   0 }
 local R = { 255,    0,   0 }
 local G = {    0, 255,   0 }
 local B = {    0,   0, 255 }
+local W = { 255,  255, 255 }
 
 local pixels_rgb_bt = {
-	{ _, _, _, _, _, B, _, B, },
-	{ _, _, _, _, _, B, B, B, },
+	{ W, W, _, _, _, B, _, B, },
+	{ W, W, _, _, _, B, B, B, },
 	{ _, _, G, G, G, B, _, B, },
 	{ _, _, G, _, G, B, B, B, },
 	{ _, R, G, _, _, _, _, _, },
@@ -139,42 +152,71 @@ local pixels_rgb_tb = {
 	{ _, R, G, _, _, _, _, _, },
 	{ _, _, G, _, G, B, B, B, },
 	{ _, _, G, G, G, B, _, B, },
-	{ _, _, _, _, _, B, B, B, },
-	{ _, _, _, _, _, B, _, B, },
+	{ W, W, _, _, _, B, B, B, },
+	{ W, W, _, _, _, B, _, B, },
 }
 
-image_rgb_bt = tga_encoder.image(pixels_rgb_bt)
-image_rgb_tb = tga_encoder.image(pixels_rgb_tb)
+local pixels_rgb_by_scanline_order = {
+	["bottom_top"] = pixels_rgb_bt,
+	["top_bottom"] = pixels_rgb_tb,
+}
 
-image_rgb_bt:save(
-	"type2_24bpp_bt.tga",
-	{ color_format="B8G8R8", compression="RAW", scanline_order = "bottom-top" }
-)
-image_rgb_tb:save(
-	"type2_24bpp_tb.tga",
-	{ color_format="B8G8R8", compression="RAW", scanline_order = "top-bottom" }
-)
-image_rgb_bt:save(
-	"type10_24bpp_bt.tga",
-	{ color_format="B8G8R8", compression="RLE", scanline_order = "bottom-top" }
-)
-image_rgb_tb:save(
-	"type10_24bpp_tb.tga",
-	{ color_format="B8G8R8", compression="RLE", scanline_order = "top-bottom" }
-)
-image_rgb_bt:save(
-	"type2_16bpp_bt.tga",
-	{ color_format="A1R5G5B5", compression="RAW", scanline_order = "bottom-top" }
-)
-image_rgb_tb:save(
-	"type2_16bpp_tb.tga",
-	{ color_format="A1R5G5B5", compression="RAW", scanline_order = "top-bottom" }
-)
-image_rgb_bt:save(
-	"type10_16bpp_bt.tga",
-	{ color_format="A1R5G5B5", compression="RLE", scanline_order = "bottom-top" }
-)
-image_rgb_tb:save(
-	"type10_16bpp_tb.tga",
-	{ color_format="A1R5G5B5", compression="RLE", scanline_order = "top-bottom" }
-)
+local tga_type_by_compression = {
+	["RAW"] = "2",
+	["RLE"] = "10",
+}
+
+local pixels_by_scanline_order_by_color_format = {
+	["A1R5G5B5"] = pixels_rgba_by_scanline_order,
+	["B8G8R8"] = pixels_rgb_by_scanline_order,
+	["B8G8R8A8"] = pixels_rgba_by_scanline_order,
+	["Y8"] = pixels_rgb_by_scanline_order,
+}
+
+for color_format, _ in pairs(
+	tga_encoder.features.color_format
+) do
+	local pixels_by_scanline_order = pixels_by_scanline_order_by_color_format[
+		color_format
+	]
+	for compression, _ in pairs(
+		tga_encoder.features.compression
+	) do
+		local tga_type
+		if (
+			"Y8" == color_format and
+			"RAW" == compression
+		) then
+			tga_type = "3"
+		else
+			tga_type = tga_type_by_compression[
+				compression
+			]
+		end
+		-- tga_encoder can not encode grayscale RLE (type 11)
+		if not(
+			"Y8" == color_format and
+			"RLE" == compression
+		) then
+			for scanline_order, _ in pairs(
+				tga_encoder.features.scanline_order
+			) do
+			local filename = "type" .. tga_type ..
+					'-' .. color_format ..
+					'-' .. scanline_order ..
+					'.tga'
+				local pixels = pixels_by_scanline_order[
+					scanline_order
+				]
+				local properties = {
+					color_format = color_format,
+					compression = compression,
+					scanline_order = scanline_order,
+				}
+				print(filename)
+				local image = tga_encoder.image(pixels)
+				image:save(filename, properties)
+			end
+		end
+	end
+end