|Introduction | Sustainability Factors | Content Categories | Format Descriptions | Contact|
|Full name||Band Interleaved by Line (BIL) Image File|
A binary raster file format for aerial photography, satellite imagery, and spectral data. The BIP data organization can handle any number of bands, and thus accommodates black and white, grayscale, pseudocolor, true color, and multi-spectral image data. Additional information is needed to interpret the image data, such as the numbers of rows, columns, and bands, if there is a color map, and latitude and longitude to relate the image to geospatial locations. This information may be supplied in a file header (typical on the legacy tapes originally used for storing satellite image data) or in a companion file, for example, as an ASCII header (.hdr) file in the ESRI implementation (See Notes). BIL is generally one member of a pair or cluster of companion files that are typically stored in the same file directory or project workspace, with all component files having the same filename and identified by individual file extension. Images stored in BIL format have pixels stored band by band for each line, or row, of the image. See BIL_enc for more specific encoding information.
|Production phase||Raster image file produced, for example, by remote sensing systems and spectrometers. It is practical to use as a middle-state format for some forms of spectral analysis. Also used as an end-state format for distribution for some US government data.|
|Relationship to other formats|
|Contains||BIL_enc, Band Interleaved by Line (BIL) Encoding|
|LC experience or existing holdings|
|Disclosure||Documentation is provided by multiple sources, including the publicly available specification from Environmental Systems Research Institute, Inc. (ESRI).|
|Documentation||Extendable Image Formats for ArcView GIS 3.1 and 3.2; ESRI White Paper, July 1999; Description of BIL/BIP/BSQ is on page 8.|
Several U.S. Government agencies and other data archives distribute geospatial data in the BIL format:
BIL spatial data can be displayed in USGS Digital Data Viewer: dlgv32 Pro a limited-feature version of commercial software Global Mapper. USGS Digital Data Viewer requires a header file (usually .hdr, .ers, or .aux) to load the BIL file. Visual rendering and write/export instructions for BIL are available in many software libraries, such as GDAL, and applications, such as AutoCAD, ESRI's ArcGIS, ENVI, Generic Database (GDB) Technology, Global Mapper, MATLAB, Oracle, etc.
|Licensing and patents||None.|
|Transparency||The raw data has a simple form and is easily interpreted if the image dimensions in pixels, the number of spectral bands, and the number of bits per band are known.|
|Self-documentation||An embedded or companion ASCII header file may contain a wide range of data regarding image capture instrumentation, date, and other data for identifying, displaying, and georeferencing the image.|
|External dependencies||Accompanying header files may be compatible only with certain software applications.|
|Technical protection considerations||No capabilities for encryption or other technical protection mechanism inherent in the format or in its use have been found by the compilers of this analysis.|
|Normal rendering||See BIL_enc|
|Clarity (high image resolution)||See BIL_enc|
|Color maintenance||See BIL_enc|
|Support for vector graphics, including graphic effects and typography||See BIL_enc|
|Support for multispectral bands||The BIL data organization can handle any number of bands, and thus accommodates black and white, grayscale, pseudocolor, true color, and multi-spectral image data. BIL data stores pixel information for separate bands within the same file, so that the user can choose to display just one specific band in a multi-band image. The Band Interleaved by Line encoding (BIL_enc) allows fairly easy access to both spatial and spectral information making it a common raster format supported by many GIS systems.|
|Functionality beyond normal rendering||When supported by suitable georeferencing information and metadata to support interpretation of spectra in accompanying files, as is often the case in practice for geospatial data, this file format supports geospatial analysis, including grid-based analysis.|
|GIS images and datasets|
|Normal functionality||BIL files are often produced by remote sensing systems and spectrometers. BIL data can be immediately read/accessed with ESRI and other GIS applications, including USGS Digital Data Viewer.|
|Support for GIS metadata||In ESRI's BIL implementation, accompanying files provide ancillary information, including metadata. In particular, projection information is provided in an ASCII text file with extension .prj. The ESRI world file, with extension .blw, is an ASCII text file containing coordinate information. It is used by some packages for geo-referencing of BIL image data. The ESRI header file, with extension .hdr, can contain a wide range of data regarding image capture instrumentation, date, and other data for identifying, displaying, and georeferencing the image.|
|Support for grids||As a raster format, data in the BIL encoding is inherently adaptable to grid-based analysis, so long as accompanying information is provided to document the scale, coordinate reference system, and projection so that the image can be registered against a grid chosen for analysis. An ESRI BIL file (with its supporting files) is easily converted to the ESRI Grid format.|
BSQ, BIL, and BIP represent alternative ways of storing images in memory or on disk. The initials stand for band-sequential, band-interleaved-by-line, and band-interleaved-by-pixel, respectively. These image formats are also sometimes called "band-interleaved", "row-interleaved", and "pixel-interleaved", respectively. Images are stored in one format or another to facilitate expected image manipulations. The BIL (band-interleaved-by-line) encoding is a compromise format, allowing fairly easy access to both spatial and spectral information.
To be interpreted properly, a BIL binary image file must have an associated ASCII header file. This header file contains ancillary data about the image such as the number of rows and columns in the image, if there is a color map, and latitude and longitude.
In ESRI applications, accompanying the BIL file are four image description files (each in ASCII text format): a header file, a statistics file, a resolution file, and a color file. The header file (.hdr) describes the nature of the image data, through the use of keywords and values. The statistics file (.stx) is an optional file that describes the image statistics for each spectral band. It records the minimum and maximum pixel values, the mean, the standard deviation, and the two linear contrast stretch parameters. The resolution file (.blw), also known as a "world file" describes the height and width of each cell and the coordinate position of the top left cell of the data. The color file (.clr) is an optional file that describes the image colormap (this file type is not used in the GPW data).