Tiff

The file header contains a signature and a link (offset) to the first substantial block of data in the file.

The file signature ( magic number ) of TIFF consists of two parts:

• Bytes 0-1 - to determine the order of bytes in the file (presented in hexadecimal notation and in text form based on ASCII encoding):
  • 49 49 (““ II “”) - in case of direct (little-endian) byte order, from the brand name of Intel processors using this order (see, for example, Intel x86 )
  • 4D 4D ("MM") - in the reverse (big-endian) order of bytes, from the name of the brand of Motorola processors that used exactly this order (see, for example, Motorola 680x0 )
• Bytes 2-3 - the identifier of the TIFF format (42 - the philosophical number (the answer to the main question of life, the universe and all that ), does not carry any meaning, in the latest version of the specification [TIFF vision 6.0 - June 3, 1992] the format always has indicated value):
  • 2A 00 - in direct byte order
  • 00 2A - in reverse byte order

Thus, there are two possible signature options (depending on the byte order in the file):

• 49 49 2A 00 - in direct byte order
• 4D 4D 00 2A - in reverse byte order

Further, bytes 4–7, the offset in bytes from the beginning of the file (aligned along the WORD ( machine word ) boundary) to the first IFD directory ( English image file directory ) is indicated.

The format structure is flexible and allows you to save images in color mode with a palette, as well as in various color spaces:

• Binary (two-color, sometimes incorrectly called black and white)
• Halftone
• With indexed palette
• RGB
• CMYK
• Ycbcr
• Cie lab

Modes of 8, 16, 32, and 64 bits per channel are supported when integer, as well as 32 and 64 bits per channel when representing pixel values with floating point numbers .

It is possible to save the image in a TIFF file with and without compression. The compression ratio depends on the features of the stored image, as well as on the algorithm used. The TIFF format allows you to use the following compression algorithms:

• PackBits ( RLE )
• Lempel-Ziv-Welch (LZW)
• Lz77
• ZIP
• Jbig
• Jpeg
• CCITT Group 3, CCITT Group 4

In this case, JPEG is simply an encapsulation of the JPEG format in the TIFF format. The TIFF format also allows you to store JPEG-compressed images without data loss (Lossless JPEG), but JPEG-LS compression is not supported in the TIFF Revision 6.0 specification.

Algorithms CCITT Group 3 and 4 are designed for encoding binary raster images . Initially, they were developed for fax networks (therefore they are sometimes called Fax 3, Fax 4). At the moment, they are also used in printing, digital cartography systems and geographical information systems. The Group 3 algorithm resembles RLE , since it encodes linear sequences of pixels , and Group 4 - two-dimensional pixel fields.

TIFF is a tag format and has the following types of labels:

Key Tags

These tags form the core of the format and must be supported by all products that implement the TIFF format in accordance with the specification.

Extended Labels

These labels form the core of the format, but, unlike the main labels, their support is optional.

Special Tags

Special tags were originally identified by Adobe . They are designed to store special data types of software manufacturers in TIFF and must be registered by Adobe.

• Libtiff
• GeoTIFF