Parent Topic: Supported File Formats

TIFF (TIF)

Most common forms of TIFF/GeoTIFF files are supported by the GeoGateway library. In particular, it is possible to read TIFF B (Bitmap), TIFF R (RGB), TIFF P (Palette), and TIFF G (Greyscale). Files with none, LZW, or PackBits compression are supported, as well as those with some other compression schemes.

TIFF G files contain one channel of imagery; TIFF B files contain a single bitmap; TIFF P files contain a single channel of imagery and a pseudocolour segment. To properly view the image, it is necessary to load both the imagery and the segment, and place the display in pseudocolour mode. TIFF R files contain three image channels (RGB).

TIFF files do not support LUTs. No descriptive data is extracted from the TIFF file, nor is any written back.

Georeferencing information in GeoTIFF format can be written to, and extracted from TIFF files. GeoTIFF is a standard being widely adopted in the geomatics industry. PCI's support includes UTM, State Plane, Geographic, Lambert Conformal Conic, Transverse Mercator, Mercator, and Oblique Mercator as well as some other projections.

If GeoTIFF information is not available, but an ESRI style TIFF world file is (with an extension of .tifw or .tfw), then it will be read for georeferencing information. However, the map units will always be set to METRE, since the world file does not contain the projection name. In addition, if the world file contains a rotation coefficient, the imported image will have incorrect georeferencing because images must be north up within the PCI system.

Also MapInfo style georeferencing is supported. MapInfo uses a .tab to store the projection definition and image georeferencing. The .tab file will have the same base name as the TIFF file.

Any uncompressed TIFF file that can be read, can also be written to; however, this is not true of compressed TIFF files which are read only.

The Tagged Image File Format (TIFF) was designed to be an extendible, all-purpose standard for image interchange. A TIFF file consists of an image with a list of information tags describing the image. A variety of image orderings is possible using TIFF files, as well as various types of compression. The TIFF format is extendible, because new information tags can be added at will; TIFF file readers are required to ignore tags they do not understand.

Because it is realistically impossible for a TIFF reader to read all possible TIFF format files, a small number of TIFF subset classifications have been developed. Requirements for reading and writing these classified files have also been developed.

Relevant classes are TIFF B (Bilevel or Bitmap), TIFF G (Grey level), TIFF P (Palette or Pseudocolour), and TIFF R (RGB).

The supported classes have a variety of possible compression schemes of which JPEG, LZW, PackBits, CCITT 3 Fax, and CCITT 4 Fax are known to work. PCI's TIFF support includes 16bit signed, and unsigned data as well as 32bit floating point in addition to the common 1 and 8 bit files.

The following are the valid configurations possible for TIFF.

Georeferencing information is exported in GeoTIFF format by default.

The following values of options are available to select different compression schemes (note that LZW is no longer supported for creation due to Patent concerns):

Normally TIFF files are written as a single image; however, with the TILED option the TIFF file can be written out as a series of smaller image tiles. This can be useful for faster localized loading of the resulting TIFF file. For instance an option value of "TILED256" would generate an image split into 256x256 pixel tiles. 

 option = "TILED256"
It is also possible append the attribute WORLD to the option value, separated from other text by a space, in order to request that an Arc/Info style TIFF World file be generated. 

 option = "WORLD"          | Uncompressed with World file
 option = "PACKBITS WORLD" | PACKBITS Compressed with World
Also an attribute option of MAPINFO can be used to create a MAPINFO .tab file which MapInfo uses to store the georeferencing information. 

 option = "PACKBITS MAPINFO" | PACKBITS with MapInfo file for georeferencing
By default, GeoTIFF information is written to every TIFF file created. Some packages can't read a TIFF file with GeoTIFF info. If this occurs, the NOGEOTIFF attribute can be added to avoid GeoTIFF information. 

 option = "NOGEOTIFF"          | Uncompressed without GeoTIFF
 option = "PACKBITS NOGEOTIFF" | PACKBITS without GeoTIFF info
PCI would like to thank Sam Leffler and SGI for providing the ``libtiff'' TIFF library, on which all of PCI's TIFF support is based. PCI would also like to thank Niles D. Ritter of the USGS who wrote the libgeotiff library on which PCI's GeoTIFF support is based.

A libtiff based suite of public domain Unix tools for dealing with TIFF files is available by anonymous ftp from www.libtiff.org on the Internet. These tools include functions to compress and uncompress TIFF files using most known TIFF compression schemes.

Information on the GeoTIFF standard can be found at the GeoTIFF web site: http://www.remotesensing.org/geotiff/geotiff.html

See Also: Works Create Panel, FIMPORT, LINK, FEXPORT

Parent Topic: Supported File Formats
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