A raster layer must be loaded into ArcMap in order to use this tool.
Selecting a conversion.
In general, it is desireable to select a conversion that uses the smallest data
type possible to represent your data. Thus you must know the range of values in your raster
(maximum and minimum) and the range of values that each data type can be used to
represent in order to select a conversion. It is recommended that users who are not
familiar with these issues read the following article: Accessing raster cell values
programmatically: the problem of mismatched data types