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|Full name||Band Sequential (BSQ) Image Encoding|
Band sequential (BSQ) is one of three primary methods for encoding image data for multiband raster images in the geospatial domain, such as images obtained from satellites. BSQ is not in itself an image format, but is a method for encoding the actual pixel values of an image in a file. BSQ format is a very simple format, where each line of the data is followed immediately by the next line in the same spectral band. This format is optimal for spatial (x,y) access of any part of a single spectral band. The BSQ 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, and relate the image to geospatial locations. This information may be supplied in a file header (typical on the tapes originally used for satellite image data) or in files associated with a raw image data file.
|Relationship to other formats|
|Used by||BSQ_file, Band Sequential (BSQ) Image File|
|Equivalent to||BIL_enc, Band Interleaved by Line (BIL) image encoding. An alternative ordering for raster image data, a widely used format that offers compromise performance for both spatial and spectral analysis.|
|Equivalent to||BIP_enc, Band Interleaved by Pixel (BIP) image encoding. An alternative ordering for raster image data, optimal for spectral access to the image data.|
|Used by||ADRG, Arc Digitized Raster Graphic. Format for maps and charts digitized from print.|
|Used by||NLAPS, NLAPS Data Format (NDF)|
|Used by||Special-purpose formats for spectral imagery, including the FAST format, developed for Landsat satellite imagery. The FAST format is not separately described on this website.|
|LC experience or existing holdings|
|Disclosure||This simple uncompressed raster data encoding is easily and frequently described, requiring no formal specification.|
A common raster image encoding for remote sensor data from satellites. The Landsat Thematic Mapper sensors and SPOT (Satellite Pour l'Observation de la Terre) have used BSQ as a primary format. The FAST Format used for Landsat data distribution is an example of the BSQ format with one or more header files and independent image files for each band. When distributed on tape, the header files and image files for each band are followed by an "End of File" marker, with an "End of Volume" marker at the end of the dataset. IRS-P6 products are distributed by Euromaps in BSQ format.
|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||The encoding can not be interpreted without external information to indicate the number of bands, the number of bits per band, number of rows and columns in the image, etc. This information is typically provided in headers or associated files. Headers or associated files may hold other forms of metadata.|
|Technical protection considerations||None for the encoding per se.|
|Normal rendering||This is a basic raster encoding. To interpret as an image, technical metadata (e.g. to define colorspace, orientation, scale) must be supplied in an accompanying data structure.|
|Clarity (high image resolution)||Spatial resolution and bit-depth are not limited by the BSQ encoding per se but may be constrained in some usage contexts.|
|Color maintenance||No support for color management in the encoding. Documentation of spectral values for bands, or interpretation of false colors (see Notes) should be supplied in an accompanying data structure.|
|Support for vector graphics, including graphic effects and typography||No support for vector graphics or special effects.|
|Support for multispectral bands||A single band covering the entire scene is stored as a single bitstream making this encoding method convenient when only selected bands are needed. Each image band can be conveniently written to an independent file. BSQ can therefore be a preferable format for some forms of analysis as an application does not have to read past ancillary data in an image stack. As opposed to formats where the bands are interleaved (such as a multi-band GeoTIFF), BSQ data sets support convenient extraction of relevant bands. Some BSQ datasets are distributed as separate image files for each band, with common geospatial registration and a shared set of header information.|
|Functionality beyond normal rendering||None.|
|GIS images and datasets|
|Normal functionality||See BSQ_file for more information regarding GIS adoption and use of this encoding, and ArcGIS Desktop Help: BIL, BIP, and BSQ Raster Files for ESRI specific information about use of this encoding in ESRI GIS products.|
|Filename extension||See related format.||See BSQ_file, Band Sequential (BSQ)Image File|
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 BSQ format is optimal for spatial access to any part of a single spectral band. The BIP format is optimal for spectral analysis. The BIL (band-interleaved-by-line) encoding is a compromise format, allowing fairly easy access to both spatial and spectral information. It is straightforward, but resource-intensive for large images, to transpose BSQ images to BIP or BIL format and vice versa.
Color maintenance in this information resource pertains to a format's support for color management, e.g., by the inclusion of ICC profiles. The intention of color management is to maximize the retention of accurate color in terms of human perception, generally expressed in terms of tristimulus values. In contrast, the color encoded in multispectral and hyperspectral imaging does not relate to tristimulus values and human perception as defined in the 1931 CIE publication. Rather, the banded colors in multispectral and hyperspectral imaging (sometimes even called "false colors") map the distribution of electromagnetic radiation at defined wavelengths (including ones not visible to the eye) in order to support scientific and technological documentation. Thus there may be a special sense in which the concept of color maintenance applies: multispectral and hyperspectral formats must document the wavelength used to "expose" each band. Metadata in or associated with the format may also document the intention. For example, mid-infrared radiation at 1550-1750 nm is often placed in one band in order to image vegetation and soil moisture content and some forest fires.
|History||BIL, BIP, and BSQ encodings were documented for use in CCT tape formats for Landsat satellite data from 1972 on. File formats for disk were developed based on experience with the tape versions.|