tga_encoder = {} local image = setmetatable({}, { __call = function(self, ...) local t = setmetatable({}, {__index = self}) t:constructor(...) return t end, }) function image:constructor(pixels) self.pixels = pixels self.width = #pixels[1] self.height = #pixels end function image:encode_colormap_spec() self.data = self.data .. string.char(0, 0) -- first entry index .. string.char(0, 0) -- number of entries .. string.char(0) -- bits per pixel end function image:encode_image_spec(properties) local color_format = properties.color_format assert( "Y8" == color_format or -- (8 bit grayscale = 1 byte = 8 bits) "A1R5G5B5" == color_format or -- (A1R5G5B5 = 2 bytes = 16 bits) "B8G8R8" == color_format or -- (B8G8R8 = 3 bytes = 24 bits) "B8G8R8A8" == color_format -- (B8G8R8A8 = 4 bytes = 32 bits) ) pixel_depth_by_color_format = { ["Y8"] = 8, ["A1R5G5B5"] = 16, ["B8G8R8"] = 24, ["B8G8R8A8"] = 32, } local pixel_depth = pixel_depth_by_color_format[color_format] assert( nil ~= pixel_depth) self.data = self.data .. string.char(0, 0) -- X-origin .. string.char(0, 0) -- Y-origin .. string.char(self.width % 256, math.floor(self.width / 256)) -- width .. string.char(self.height % 256, math.floor(self.height / 256)) -- height .. string.char(pixel_depth) .. string.char(0) -- image descriptor end function image:encode_header(properties) local color_format = properties.color_format local compression = properties.compression local image_type if "Y8" == color_format and "RAW" == compression then image_type = 3 -- grayscale elseif ( "A1R5G5B5" == color_format or "B8G8R8" == color_format or "B8G8R8A8" == color_format ) then if "RAW" == compression then image_type = 2 -- RAW RGB(A) elseif "RLE" == compression then image_type = 10 -- RLE RGB end end assert( nil ~= image_type ) self.data = self.data .. string.char(0) -- image id .. string.char(0) -- color map type .. string.char(image_type) self:encode_colormap_spec() -- color map specification self:encode_image_spec(properties) -- image specification end function image:encode_data(properties) local color_format = properties.color_format local compression = properties.compression local data_length_before = #self.data if "Y8" == color_format and "RAW" == compression then if 8 == self.pixel_depth then self:encode_data_Y8_as_Y8_raw() elseif 24 == self.pixel_depth then self:encode_data_R8G8B8_as_Y8_raw() end elseif "A1R5G5B5" == color_format then if "RAW" == compression then self:encode_data_R8G8B8_as_A1R5G5B5_raw() elseif "RLE" == compression then self:encode_data_R8G8B8_as_A1R5G5B5_rle() end elseif "B8G8R8" == color_format then if "RAW" == compression then self:encode_data_R8G8B8_as_B8G8R8_raw() elseif "RLE" == compression then self:encode_data_R8G8B8_as_B8G8R8_rle() end elseif "B8G8R8A8" == color_format then if "RAW" == compression then self:encode_data_R8G8B8A8_as_B8G8R8A8_raw() end end local data_length_after = #self.data assert( data_length_after ~= data_length_before, "No data encoded for color format: " .. color_format ) end function image:encode_data_Y8_as_Y8_raw() assert(8 == self.pixel_depth) local raw_pixels = {} for _, row in ipairs(self.pixels) do for _, pixel in ipairs(row) do local raw_pixel = string.char(pixel[1]) raw_pixels[#raw_pixels + 1] = raw_pixel end end self.data = self.data .. table.concat(raw_pixels) end function image:encode_data_R8G8B8_as_Y8_raw() assert(24 == self.pixel_depth) local raw_pixels = {} for _, row in ipairs(self.pixels) do for _, pixel in ipairs(row) do -- the HSP RGB to brightness formula is -- sqrt( 0.299 r² + .587 g² + .114 b² ) -- see local gray = math.floor( math.sqrt( 0.299 * pixel[1]^2 + 0.587 * pixel[2]^2 + 0.114 * pixel[3]^2 ) + 0.5 ) local raw_pixel = string.char(gray) raw_pixels[#raw_pixels + 1] = raw_pixel end end self.data = self.data .. table.concat(raw_pixels) end function image:encode_data_R8G8B8_as_A1R5G5B5_raw() assert(24 == self.pixel_depth) local raw_pixels = {} -- Sample depth rescaling is done according to the algorithm presented in: -- local max_sample_in = math.pow(2, 8) - 1 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 + ((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) local raw_pixel = string.char(colorword % 256, math.floor(colorword / 256)) raw_pixels[#raw_pixels + 1] = raw_pixel end end self.data = self.data .. table.concat(raw_pixels) end function image:encode_data_R8G8B8_as_A1R5G5B5_rle() assert(24 == self.pixel_depth) local colorword = nil local previous_r = nil local previous_g = nil local previous_b = nil local raw_pixel = '' local raw_pixels = {} local count = 1 local packets = {} local raw_packet = '' local rle_packet = '' -- Sample depth rescaling is done according to the algorithm presented in: -- local max_sample_in = math.pow(2, 8) - 1 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 nil ~= previous_r then colorword = 32768 + ((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) if 1 == count then -- remember pixel verbatim for raw encoding raw_pixel = string.char(colorword % 256, math.floor(colorword / 256)) raw_pixels[#raw_pixels + 1] = raw_pixel if 128 == #raw_pixels then raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} end else -- encode raw pixels, if any if #raw_pixels > 0 then raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} end -- RLE encoding rle_packet = string.char(128 + count - 1, colorword % 256, math.floor(colorword / 256)) packets[#packets +1] = rle_packet end end count = 1 previous_r = pixel[1] previous_g = pixel[2] previous_b = pixel[3] else count = count + 1 end end end colorword = 32768 + ((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) if 1 == count then raw_pixel = string.char(colorword % 256, math.floor(colorword / 256)) raw_pixels[#raw_pixels + 1] = raw_pixel raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} else -- encode raw pixels, if any if #raw_pixels > 0 then raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} end -- RLE encoding rle_packet = string.char(128 + count - 1, colorword % 256, math.floor(colorword / 256)) packets[#packets +1] = rle_packet end self.data = self.data .. table.concat(packets) end function image:encode_data_R8G8B8_as_B8G8R8_raw() assert(24 == self.pixel_depth) local raw_pixels = {} for _, row in ipairs(self.pixels) do for _, pixel in ipairs(row) do local raw_pixel = string.char(pixel[3], pixel[2], pixel[1]) raw_pixels[#raw_pixels + 1] = raw_pixel end end self.data = self.data .. table.concat(raw_pixels) end function image:encode_data_R8G8B8_as_B8G8R8_rle() assert(24 == self.pixel_depth) local previous_r = nil local previous_g = nil local previous_b = nil local raw_pixel = '' local raw_pixels = {} local count = 1 local packets = {} local raw_packet = '' local rle_packet = '' 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 nil ~= previous_r then if 1 == count then -- remember pixel verbatim for raw encoding raw_pixel = string.char(previous_b, previous_g, previous_r) raw_pixels[#raw_pixels + 1] = raw_pixel if 128 == #raw_pixels then raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} end else -- encode raw pixels, if any if #raw_pixels > 0 then raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} end -- RLE encoding rle_packet = string.char(128 + count - 1, previous_b, previous_g, previous_r) packets[#packets +1] = rle_packet end end count = 1 previous_r = pixel[1] previous_g = pixel[2] previous_b = pixel[3] else count = count + 1 end end end if 1 == count then raw_pixel = string.char(previous_b, previous_g, previous_r) raw_pixels[#raw_pixels + 1] = raw_pixel raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} else -- encode raw pixels, if any if #raw_pixels > 0 then raw_packet = string.char(#raw_pixels - 1) packets[#packets + 1] = raw_packet for i=1, #raw_pixels do packets[#packets +1] = raw_pixels[i] end raw_pixels = {} end -- RLE encoding rle_packet = string.char(128 + count - 1, previous_b, previous_g, previous_r) packets[#packets +1] = rle_packet end self.data = self.data .. table.concat(packets) end function image:encode_data_R8G8B8A8_as_B8G8R8A8_raw() assert(32 == self.pixel_depth) local raw_pixels = {} for _, row in ipairs(self.pixels) do for _, pixel in ipairs(row) do local raw_pixel = string.char(pixel[3], pixel[2], pixel[1], pixel[4]) raw_pixels[#raw_pixels + 1] = raw_pixel end end self.data = self.data .. table.concat(raw_pixels) end function image:encode_footer() self.data = self.data .. string.char(0, 0, 0, 0) -- extension area offset .. string.char(0, 0, 0, 0) -- developer area offset .. "TRUEVISION-XFILE" .. "." .. string.char(0) end function image:encode(properties) self.data = "" self:encode_header(properties) -- header -- no color map and image id data self:encode_data(properties) -- encode data -- no extension or developer area self:encode_footer() -- footer end function image:save(filename, properties) local properties = properties or {} properties.compression = properties.compression or "RAW" self.pixel_depth = #self.pixels[1][1] * 8 if nil == properties.color_format then if 8 == self.pixel_depth then properties.color_format = "Y8" elseif 24 == self.pixel_depth then properties.color_format = "B8G8R8" elseif 32 == self.pixel_depth then properties.color_format = "B8G8R8A8" end end assert( nil ~= properties.color_format ) self:encode(properties) local f = assert(io.open(filename, "wb")) f:write(self.data) f:close() end tga_encoder.image = image