🐥 Creating an empty PNG in Elixir

If you ever need a way to create an empty PNG in Elixir, this will do the trick:

defmodule EmptyPNG do
  def generate() do
    <<137, 80, 78, 71, 13, 10, 26, 10>> <>
    ihdr_chunk() <>
    idat_chunk() <>
    iend_chunk()
  end

  defp ihdr_chunk() do
    width = 1
    height = 1
    bit_depth = 8
    color_type = 6 # RGBA
    compression = 0
    filter = 0
    interlace = 0

    data =
      <<width::big-32, height::big-32, bit_depth, color_type, compression, filter, interlace>>

    chunk("IHDR", data)
  end

  defp idat_chunk() do
    # 1x1 pixel with RGBA(0,0,0,0) (fully transparent)
    pixel_data = <<0, 0, 0, 0, 0>>  # PNG filter type (0) + RGBA (4 bytes)

    compressed = :zlib.compress(pixel_data)
    chunk("IDAT", compressed)
  end

  defp iend_chunk(), do: chunk("IEND", <<>>)

  defp chunk(type, data) do
    length = byte_size(data)
    crc = :erlang.crc32(type <> data)

    <<length::big-32>> <> type <> data <> <<crc::big-32>>
  end
end

To get the raw bytes of an empty PNG, execute:

EmptyPNG.generate()

This generates a minimal 1x1 transparent PNG using the PNG format specification.