ARCTAN replaces every pixel in source by the arctangent of the original value. The result of ARCTAN is in degrees from -90 to +90 by default. If you wish the arctangent values to lie between 0 and 180 degrees, use the keyword 0TO180.
![\begin{command}
\item[\textbf{Form:} ARCTAN source {[0TO180]}\hfill]{}
\end{command}](img216.png){kind=small}