エスケープシーケンスの背景色で描画してみた。
24bitカラーと8bitカラーだけ、パースも適当だけど・・・

環境はWindows10(1903) + Windows標準のコマンドプロンプト + nyagos

最初、1byteずつ読み込んでいたんだけど、どうも取りこぼしているようだったので
最初に全部読み込んでからパースしてます。

nyagos.alias.bmp = function(args)
  local bmp = io.open(args[1], 'r'):read('*a')

  -- Headr
  local p = 1
  p = p + 2 -- BM
  p = p + 4 -- File Size
  p = p + 2 -- Reserved
  p = p + 2 -- Reserved
  local offset = bmp:byte(p, p + 1)
  p = p+ 1
  offset = offset + bmp:byte(p, p + 1) * 0x100
  p = p + 1
  offset = offset + bmp:byte(p, p + 1) * 0x10000
  p = p + 1
  offset = offset + bmp:byte(p, p + 1) * 0x1000000
  p = p + 1
  p = p + 4 -- Info Header Size
  local width = bmp:byte(p, p + 1)
  p = p + 1
  width = width + bmp:byte(p, p + 1) * 0x100
  p = p + 1
  width = width + bmp:byte(p, p + 1) * 0x10000
  p = p + 1
  width = width + bmp:byte(p, p + 1) * 0x1000000
  p = p + 1
  local height = bmp:byte(p, p + 1)
  p = p + 1
  height = height + bmp:byte(p, p + 1) * 0x100
  p = p + 1
  height = height + bmp:byte(p, p + 1) * 0x10000
  p = p + 1
  height = height + bmp:byte(p, p + 1) * 0x1000000
  p = p + 1
  p = p + 2 -- Plane. always 1
  local bits = bmp:byte(p, p + 1)
  p = p + 1
  bits = bits + bmp:byte(p, p + 1) * 0x100
  p = p + 1
  local is24bit = false
  local is8bit = false
  if bits == 24 then
    is24bit = true
  elseif bits == 8 then
    is8bit = true
  else
    print("Unsupported format")
    return
  end
  p = p + 4 -- Compress
  p = p + 4 -- Data Size
  p = p + 4 -- Resolution
  p = p + 4 -- Resolution
  local palleteSize = bmp:byte(p, p + 1)
  p = p + 1
  palleteSize = palleteSize + bmp:byte(p, p + 1) * 0x100
  p = p + 1
  palleteSize = palleteSize + bmp:byte(p, p + 1) * 0x10000
  p = p + 1
  palleteSize = palleteSize + bmp:byte(p, p + 1) * 0x1000000
  p = p + 1
  p = p + 4 -- Important Color
  local pallete = {}
  for i = 1, palleteSize, 1 do
    pallete[i] = {}
    pallete[i][1] = bmp:byte(p, p + 1);
    p = p + 1
    pallete[i][2] = bmp:byte(p, p + 1);
    p = p + 1
    pallete[i][3] = bmp:byte(p, p + 1);
    p = p + 1
    pallete[i][4] = bmp:byte(p, p + 1);
    p = p + 1
  end
  p = offset + 1

  -- Data
  local img = {}
  for j = 1, height, 1 do
    img[height-j+1] = {}
    local r, g, b
    for i = 1, width, 1 do
      if is24bit then
        b = bmp:byte(p, p + 1)
        p = p + 1
        g = bmp:byte(p, p + 1)
        p = p + 1
        r = bmp:byte(p, p + 1)
        p = p + 1
      elseif is8bit then
        local pp = bmp:byte(p, p + 1)
        p = p + 1
        if pp ~= nil then
          b = pallete[pp + 1][1]
          g = pallete[pp + 1][2]
          r = pallete[pp + 1][3]
        end
      end
      img[height-j+1][i] = '\027[48;2;' .. r .. ';' .. g .. ';' .. b .. 'm  \027[49m'
    end
    -- padding
    if is24bit then
      p = p + width % 4
    elseif is8bit then
      p = p + (width * 3) % 4
    end
  end
  for _, r in pairs(img) do
    for _, c in pairs(r) do
      nyagos.write(c)
    end
    nyagos.write('\n')
  end
end