Band Properties

Rasters contain a set of metadata that defines the properties for each band. These properties include the band name, number of palettes, interpretation, bit depth, nodata value, and properties relating to the preferred method of data access.

The interpretation of a band describes the type of data stored at each cell in the raster and number of bits used for that type. An interpretation also implies an underlying fundamental data type used to store the data. For example, an interpretation Gray8 implies that the actual data type is FME_UInt8 and that the size of each cell is 8 bits. Possible interpretation values are Int8, Int16, Int32, Int64, UInt8, UInt16, UInt32, UInt64, Real32, Real64, Gray8, Gray16, Red8, Red16, Green8, Green16, Blue8, Blue16, Alpha8, Alpha16.

Many raster formats store a single data value called nodata, transparent or background value that represents unknown or invalid data. Often the value is at one of the extremes of the data type range. Some formats may specify a particular nodata value that is unique to that format, while others are capable of handling any single value designated as nodata.

A second option for nodata specification is a whole band or bitmask of data that acts as a flag for each cell, indicating whether or not the cell is valid data. Several formats do not support nodata values at all.

Bands may also have multiple palettes associated with each instance. The number of palettes on a band can be determined as part of the band properties.