Available with Image Analyst license.
Available with Spatial Analyst license.
Overview
Calculates the natural logarithm (base e) of each pixel in a raster.
Notes
The natural logarithm (Ln) is the most commonly used logarithmic function.
The input Raster can be an integer or a floating point. The output of this tool is always a floating point, regardless of the input type.
Input values that are 0 or negative will be NoData in the output raster.
If the input is a multiband raster, the output will be a multiband raster. The function will perform the operation on each band in the input.
If the input is a multidimensional raster, all slices from all variables will be processed, and the output will be a multidimensional raster.
Parameters
Parameter name  Description 

Raster  Input values for which to find the natural logarithm (Ln). 
Extent Type  Choose which extent should be used in the output raster:

Cellsize Type  Choose which cell size to use in the output raster. If all the input cell sizes are the same, all the options will yield the same results.
