Level 2 Help for GRADREM

START specifies the starting line of the region used to estimate the gradient.
The default is 1.

LENGTH specifies the length of the region used to estimate the gradient.  The
default is for the entire picture to be used (as determined by the SIZE field).

Every LINC-th line will be used to estimate the gradient.  Default is 1.

FILT selects box filtering in order to smooth the gradient function, and
specifies the weight.  The default is not to perform any smoothing.

The output DN for any pixel is given by the formula
		 DNout = GAIN * (DNin / gradient) + OFFset.
GAIN specifies the factor to be used in the computation.  If OFF (the offset)
is specified, but GAIN isn't, the gain defaults to 100.0.  If neither GAIN nor
OFF is specified, and the user doesn't select the PERCENT or NOSAT options,
the gain is set to the input's mean DN value.

The output DN for any pixel is given by the formula
		 DNout = GAIN * (DNin / gradient) + OFFset.
OFF specifies the offset to be used in the computation.  The default 
offset is 0.0.

When this parameter is specified, the program will compute and use values
for GAIN and OFF which will lead to PERCENT percent saturation in the output
picture.

'NOPRINT suppresses the printing of the computer gradient function.

The 'NOSAT option sets the offset to zero and chooses a gain such that no
unsaturated input pixel becomes saturated in the output image.

MEANSIG has two values: the first is the desired mean for each sample (column)
in the gradient estimation region.  The second value is the desired 
standard deviation for this region.  In this mode, GRADREM forces a gradient
removal to best approximate these values.