Smallest things

The collection of smallest things, where the word smallest can be proved and verified. See also short codes for the collection of small codes.

Smallest PNG file

It’s 67 bytes long:

PNG Header:
    0000: 89 50 4E 47 0D 0A 1A 0A       "\x89PNG\r\n\x1a\n"

IHDR Chunk:
    0008: 00 00 00 0D                   Size of this chunk (13)
    000C: 49 48 44 52                   "IHDR"
    0010: 00 00 00 01                   Width (1px)
    0014: 00 00 00 01                   Height (1px)
    0018: 08                            Bit depth (8 bits per pixel)
    0019: 06                            Color type (truecolor with alpha)
    001A: 00                            Compression method (deflate)
    001B: 00                            Filter method (adaptive filtering)
    001C: 00                            Interlace method (none)
    001D: 1F 15 C4 89                   CRC of this chunk

IDAT Chunk:
    0021: 00 00 00 0A                   Size of this chunk (10)
    0025: 49 44 41 54                   "IDAT"
    0029: 78                            zlib header (CMF): DEFLATE, 32 KiB window
    002A: 9C                            zlib header (FLG): no preset, default level
    002B: 63 00 01 00                   zlib contents for "00 00 00 00 00"
          <-LSB  MSB->                  (filter type 0, rgba(0,0,0,0))
          +----------+
          | 1        | ---------------- Final block
          |  10      | ---------------- Huffman coding block with fixed codes
          |    00110 | -+-------------- Literal byte 00 (code 0)
          | 000      | -'
          |    00000 | -+-------------- Reference with length=4 (code 258)
          | 10       | -'
          |   00000  | ---------------- ...and distance=1
          |        0 | -.
          | 000000   | -+-------------- End of block (code 256)
          |       00 | ---------------- Padding
          +----------+
    002F: 00 05 00 01                   zlib Adler-32 checksum
    0033: 0D 0A 2D B4                   CRC of this chunk

IEND Chunk:
    0037: 00 00 00 00                   Size of this chunk (0)
    003B: 49 45 4E 44                   "IEND"
    003F: AE 42 60 82                   CRC of this chunk

This file contains a transparent pixel, but the smallest PNG file with a black or white pixel has the same size (using grayscale).

This file is the smallest because:

• The PNG specification requires every PNG file at least three basic chunks: IHDR, IDAT, IEND.
• The sizes of IHDR and IEND chunks are fixed.
• Introducing a new chunk requires at least 12 additional bytes. This rejects the use of indexed color (PLTE chunk) and non-alpha-channel transparency (tRNS chunk).
• Thus we need at least 5 bytes of data to be compressed.
• The zlib header is always 2 bytes long.
• DEFLATE has three coding methods, but since the raw data is a bit large and requires the string duplication, “no compression” cannot be used.
• The other coding method, dynamic Huffman code, requires a Huffman tree for that code. Since this requires at least 26 bits¹ of overheads, compared to 23 bits for beating the static Huffman code, this possibility is also ruled out.