tga_encoder = {} local image = setmetatable({}, { __call = function(self, ...) local t = setmetatable({}, {__index = self}) t:constructor(...) return t end, }) function image:constructor(pixels, properties) local properties = properties or {} local pixel_depth = properties.pixel_depth or 16 self.data = "" self.pixels = pixels self.width = #pixels[1] self.height = #pixels self:encode(pixel_depth) 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(pixel_depth) assert( 16 == pixel_depth or -- (A1R5G5B5 = 2 bytes = 16 bits) 24 == pixel_depth -- (B8G8R8 = 3 bytes = 24 bits) ) 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(pixel_depth) self.data = self.data .. string.char(0) -- image id .. string.char(0) -- color map type .. string.char(10) -- image type (RLE RGB = 10) self:encode_colormap_spec() -- color map specification self:encode_image_spec(pixel_depth) -- image specification end function image:encode_data(pixel_depth) if 16 == pixel_depth then self:encode_data_a1r5g5b5_rle() elseif 24 == pixel_depth then self:encode_data_r8g8b8_rle() end end function image:encode_data_a1r5g5b5_rle() 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_rle() 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_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(pixel_depth) self:encode_header(pixel_depth) -- header -- no color map and image id data self:encode_data(pixel_depth) -- encode data -- no extension or developer area self:encode_footer() -- footer end function image:save(filename) local f = assert(io.open(filename, "wb")) f:write(self.data) f:close() end tga_encoder.image = image