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Affinity .afpalette format

Affinity Designer / Photo palette files are a little-endian binary format made of tagged chunks. Ocular reads versions 8–20 and writes version 8 swatch palettes compatible with Affinity 2.

File layout

Region Size Description
Header 80 bytes Magic, version, size fields, metadata chunks
Body variable Palette name, swatch count, color data, swatch names
End marker 5 bytes 00 FF FF FF FF
#FAT footer 107 bytes Metadata, size fields, CRC32, Swatches.dat path

The last 115 bytes on disk are often described as the “footer” in other tools: that span includes any trailing name bytes, the end marker, and the #FAT chunk.

Header (80 bytes)

Offset Type Field
0 uint32 Magic 0x414BFF00 (00 FF 4B 41)
4 uint32 Format version (8 in files written by Ocular)
8 char[4] htwS
12 char[4] #Inf
16 uint64 Offset of #FAT chunk (patched on save)
24 uint64 Total file size (patched on save)
32 uint64 CRC length: file_size − 80 − 107 (patched on save)
48 uint32 Unix datestamp placeholder (0x544E4DEB in templates)
… … Prot, #Fil, KS tags (fixed in v8 template)

Body

After the header:

  1. VlaP wrapper — 01 00 + VlaP + 01 00
  2. +NClP — tag 2B 4E 43 6C 50, then uint32 UTF-8 length and palette name
  3. B1VlaP — byte 0xB1 + VlaP, then uint32 swatch count
  4. Swatch prefix — 01 00 00 00 00 00 before the first color
  5. Color swatches — linked list of SliF / 1rloC blocks (see below)
  6. VNaP names — byte 0xAB, tag VNaP, block size, count, then length-prefixed UTF-8 names

Swatch chaining

The first swatch uses a longer SliF / lliF / 1rloC / ABAL header. Each following swatch is a shorter SliF + 1rloC block. After every swatch except the last, six bytes link to the next index: 01 NN 00 00 00 01 where NN = swatch_index × 2.

Color encodings (read)

Ocular scans for type tags after rloC markers:

Tag Location tag Data
ABGR Dloc_ Three float32 RGB (0–1)
ABAL <loc_ Three uint16 Lab (scaled 0–65535)
KYMC Hloc_ Four float32 CMYK
ALSH Dloc_ Three float32 HSL
YARG <loc_ One float32 gray

Color encoding (write)

Swatches are written as ABAL with Lab values derived from RGB via rgb2lab, then a <loc_ block and suffix FF FF 00 00.

#FAT footer (107 bytes)

Starts with tag #FAT (23 46 41 54). Important patched fields (relative to #FAT):

Offset Type Value
20 uint64 File size
28 uint64 CRC length
72 uint64 CRC length (duplicate)
80 uint64 CRC length (duplicate)
88 uint32 CRC32 checksum

Ends with a length-prefixed Swatches.dat path (0x0C 00 + "Swatches.dat").

CRC32

Affinity 2 validates the file checksum.

  • Polynomial: 0xEDB88320 (standard CRC-32)
  • Range: byte offset 76 for file_size − 80 − 107 bytes (includes the last four header bytes and the body through the end marker)
  • Stored at: #FAT + 88
crc = CRC32(data[76 .. 76 + crc_length])

Related formats

Gradient-heavy palettes may use version 11, a #FT4 footer (115 bytes), and ABGR floats instead of ABAL Lab swatches.

Ocular’s writer targets simple v8 swatch palettes (#FAT).

Implementation

read_afpalette_palette and save_afpalette_palette in lib/palette.c.