Erdas Imagine
A raster data format used in ERDAS IMAGINE software.
Erdas Imagine is a specific raster data format that is used primarily in ERDAS imagine software, created by Hexagon Geospatial. The format is specifically designed to process, analyze and manage raster data. The files are typically stored with .img file extension, reflecting its primary purpose as a storage medium for image data.
Raster data comprises grid cells or pixels, each of which contains a specific value. In a grayscale image, for instance, the raster data values might represent varying shades of gray, with each pixel's value indicating its specific shade. For multispectral imagery such as most satellite photographs, each pixel's value might contain multiple bands of information symbolizing different irradiance levels at different electromagnetic spectrum wavelengths.
One of the essential features of Erdas Imagine format (.img) is its capability to store multiple bands of data. This characteristic becomes crucial when dealing with remotely sensed imagery like satellite and aerial imagery, where data is captured in different spectral bands. Each spectral band is stored as a separate layer in the raster dataset, allowing for intricate analysis and processing of data.
Erdas Imagine (.img) data format also supports multiple data types such as 8-bit unsigned integers, 16-bit signed/unsigned integers, 32-bit signed/unsigned integers, and 32-bit/64-bit floating points. This attribute allows users to store pixel values in a data range that is suitable for a particular analysis. For example, 8-bit unsigned integers can be used to store values from 0 to 255 while 32-bit floating point numbers can store values with decimal places.
Another trait of Erdas Imagine (.img) is the format's pyramiding feature. This feature creates a pyramid of levels for the image – the lowest level being the full resolution image and the highest level being a general overview. The pyramid data structure is efficient for viewing large images because it only needs to access the amount of image data that is necessary to display in the view window. Also, this feature allows for faster zooming and panning of images without loss of quality.
In addition, the Erdas Imagine format supports auxiliary data files that may contain georeference information, coordinate system definitions, spatial indices, and statistics. These auxiliary files have the same base name as the .img file but with different extensions like .ige, .rrd, .aux.xml, and so on. These additional files are crucial in providing context to the raw image data and enhancing its information content.
Erdas Imagine is a proprietary format, and while it is primarily intended for use with Hexagon Geospatial's ERDAS Imagine software, it can also be read and written by other platforms, including GDAL (Geospatial Data Abstraction Library) supported software such as Quantum GIS, or R software with packages like rgdal and raster.
In summary, Erdas Imagine (.img) is a versatile and capable data format for managing, processing, and analysing raster datasets, particularly imagery data from remote sensing
