The bit depth (pixel depth) of a pixel 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 that 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 |
Unsigned 64 bit | 0 to 18446744073709551616 |
An additional type of bit depth, called complex, is supported for reading and displaying purposes. This bit depth exists in a number of raster formats, including radar formats such as Radarsat, and .gff.
Esri products contain all the designations of unknown values within their raster datasets. The unknown values are NoData. Internally, a real value must be used to store the NoData pixels. Accordingly, when NoData is added to a raster that already has a full bit range (meaning that there is at least one pixel in the raster extent occupying all the values in the bit range, for example, when 0 to 255 are all represented), it is promoted to the next higher bit depth. For example, a hillshade grid with cell values of 0 to 255 (which would otherwise fit within the 8 bit range), that also contains some NoData cells, is represented as unsigned 16 bit.