Introduction
TIFF format is widely accepted versatile raster data format in the world today. TIFF is a suitable format for storage, transfer, display, and printing of raster images such as clipart, logotypes, scanned documents etc.. The TIFF imagery file format can be used to store and transfer digital satellite imagery, scanned aerial photos, elevation models, and scanned maps.
Looking into popularity of TIFF, many TIFF users those who were using TIFF format to store digital satellite images felt the requirement of somehow embedding Geographic information (latitude, longitude, map projection etc.) into TIFF file so that it can be used by various GIS packages with ease. This requirement prompted the development of GeoTIFF, the TIFF file that has geographic (or cartographic) data embedded as tags within the TIFF file. The geographic data of a GeoTIFF file can be used to position the image in the correct location and geometry on the screen of a geographic information display. Since GeoTIFF is based on TIFF this paper describes TIFF for the sake of completeness.
TIFF (Tagged Image File Format)
TIFF is a tag-based file format for storing and interchanging raster images. Aldus Corporation published the first version of TIFF specification in 1986, after a series of meetings with various scanner manufactures and software developers. TIFF is to describe and store raster image data. The main advantages of TIFF is its suitability for a wide range of applications and its independence of computer's architecture, operating system, and graphics hardware. It is reasonably compact and handles black-and-white, grayscale, and color images, allowing a user to adjust for the unique characteristics of a scanner, monitor, or printer. TIFF allows color resolution up to 48 bits (a 16-bit field each for R, G, and B), either as full RGB color or in a 64k-color palette .The TIFF 6.0 specifications, released in June 1992 is taken as reference by GeoTIFF.
Overview of TIFF File Structure
The TIFF format [1] has a three-level hierarchy as shown in Fig. 1. From highest to lowest, the levels are:
- A file Header.
- One or more directories called IFDs (Image File Directories), containing codes and their data, or pointer to the data.(Table 1)
- Data.
The File Header
The TIFF file begins with an 8-byte header, which gives basic information about the file such as byte order (Little Endian or Big Endian), TIFF file ID or Version Number (which is always 42) and a pointer to first IFD.