Bit depth capacity for raster dataset cells
Release 9.2 Last modified September 22, 2008	Print all topics in : "Properties of raster data"

The bit depth (also known as pixel depth) of a cell determines the range of values that a particular raster file can store, which is based on the formula 2ⁿ (where n is the bit depth). For example, an 8-bit raster can have 256 unique values, which range from 0 to 255.

The following table shows the range of values stored for different bit depths.

Bit depth	Range of values that each cell can contain
1 bit	0 to 1
2 bit	0 to 3
4 bit	0 to 15
Unsigned 8 bit	0 to 255
Signed 8 bit	-128 to 127
Unsigned 16 bit	0 to 65535
Signed 16 bit	-32768 to 32767
Unsigned 32 bit	0 to 4294967295
Signed 32 bit	-2147483648 to 2147483647
Floating-point 32 bit	-3.402823466e+38 to 3.402823466e+38

There are exceptions to this that are hidden from the user. A grid dataset is always 32 bit (either signed, unsigned, or floating point), but ArcGIS shows it as being the most appropriate bit depth above (with regard to the cell values it contains); ArcInfo Workstation will always tell you the bit depth of the grid.

ESRI's products contain all the designations of unknown values within its raster datasets. The unknown values are called NoData. Internally, a real value must be used to store the NoData cells. Accordingly, when NoData is added to a raster that already has a full-bit range (meaning that there is at least one cell in the raster extent occupying all the values in the bit range, for example, when 0 thru 255 are all represented), it will be promoted to the next higher bit depth. For example, a hillshade grid with cell values of 0 to 255, which then has NoData added to it, will be represented as unsigned 16 bit.
Learn more about the technical specifications for raster formats
Learn more about NoData in raster datasets
Learn about 1-bit TIFFs

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