Edit from 2020 : I was recently made aware that the ZIF file format is in fact a subset of BigTiff. For end users, what this means is that it can easily be opened by many image viewing and manipulation softwares (such as GIMP) by simply changing the file extension from .zif to .tiff.

ZIF

zoomify ZIF (ZoomifyImageFormat) file format documentation and tools.

Tools

ZIF.js

This repository hosts a implementation of the format in Ecmascript6. You can try it online here: http://lovasoa.github.io/ZIF/.

Zif.reader

@asherber wrote a parser class for the format in C#, under the GPL. You can find it here: https://github.com/asherber/Zif.Reader

About the format

The ZIF file format is used by zoomify as a single-file zoomable image format. A zif file represents a single image. It contains JPEG tiles, little square images that represent a part of the image at a given zoom level, as well as meta-information about how the tiles are organized. More about the concept behind zoomify.

ZIF file format documentation

I have partially reverse-engineered the format. Here is what I found.

Data types

All numbers are stored in little endian (the number 0xABCD is sored as 0xCD 0xAB).

Term | Signification -------------|--------------- long | 8 bytes unsigned int (uint64) int | 4 bytes unsigned int (uint32) short | 2 bytes unsigned int (uint16) pointer | a long representing an offset in bytes from the beginning of the file

Header

Magic bytes

The first 16 bytes of the file are always

49 49 2B 00 08 00 00 00

Metadata

Meta-data start at offset 0x8 in the file. There is a set of metadata for every zoom level (tier).

Zoomlevel metadata

Each set of metadata starts with a long pointer to a long number representing the number of tags (single metadata) in the zoom level. Usually this is a pointer to the offset n + 8, where n is the offset in bytes of the beggining of the metadata set (so, most often *n == n+8). Then, the real metadata start right after the metadata count (at *n + 8, which is usually equal to n + 16).

The last zoomlevel has its pointer to the next zoomlevel set to 0.

Each tag is 20 bytes long.

Offset (from the start of the tag) | Length (in bytes) | Data -----------------------------------|-------------------|------------------------------ 0 | 2 (short) | Magic number identifying the tag type 2 | 2 | Unknown (but not null) 4 | 8 (long) | value 1 12 | 8 (long) | value 2

Tag types

Magic number in decimal | Magic bytes | Signification of value 1 | Signification of value 2 -----|---|---|--- 256 |0x00 0x01| ? | Image width at this zoomlevel 257 |0x01 0x01| ? | Image height at this zoomlevel 322 |0x42 0x01| ? | Tile width 323 |0x43 0x01| ? | Tile height 324 |0x44 0x01| Number of tiles | Pointer to the tile offsets index (see note below) 325 |0x45 0x01| Number of tiles | Pointer to the tile sizes index (see note below)

Note about tag 324 (tile offsets index pointer)

For tag 324, if value1 is 1 (there is only 1 tile in the zoomlevel), then value2 is not a pointer to a tile offsets index, but a tile index directly.

Note about tag 325 (tile sizes index pointer)

For tag 325, if value1 is inferior to 3 (there are only 1 or 2 tiles in the tier), then value2 is not a pointer to the tile sizes index, but is split in two int values, representing the JPEG tile sizes in bytes directly. It is then as if the tile sizes index were at the offset of value2.

Tile offsets index

Simple list of pointers (8 bytes file offsets) to the beginning of tiles. Each tile is a simple JPEG file.

Tile sizes index

Simple list of ints indicating tile sizes (in bytes).