- Form:SQRT source [SGN] [SIGN] [NOABS]
SQRT replaces each pixel in 'source' by the square root of the pixel value.
If there are negative pixels, the square root of the absolute value is
taken, unless the NOABS keyword is given, in which case negative pixels are
set to zero, or unless the words SGN or SIGN are included. If either if
these words are included on the command line, the square root of the
absolute value is computed and given a negative sign (example: -4 turns
into -2).