Level 2 Help for RATIO

INP specifies the input data sets, of which there must be two.

OUT specifies the output data set, if any.  If none is specified, the gain and
offset and computed and printed, but F2 is not called and no output data set
is written.

Specifying NOCENTER forces the saturation level of the output image to be at
the requested level on both ends. Specifying CENTER (the default) forces the
output mean to be at 128 DN, and the saturation level to be at the requested
level at one end, and less at the other.

MODE may be used to specify whether calculations are to be based on differences
or ratios between the two input images.  If the user asserts MODE=DIFF or 'DIFF
the differences mode will be invoked.  Otherwise the program will use ratioing.

MODE2=LOG and 'LOG both specify that the natural log of the difference or ratio
should be calculated.

AREA causes the program to sample only within the region specified.  The
default is to use the whole image for sampling.

SAMPLE indicates the percentage of lines within the sampling area which will be
sampled.  All samples on a chosen line are sampled.  The default is 5 percent.

LINC specifies the line increment to use in sampling lines.

The INCLUDE option may be used to include only a certain range of values for
statistical calculations.  The default range for ratios is [0.0,5.0], and for
differences, [-249.5,250.5].  If the LOG option is used, INCLUDE applies
to the value before the logarithm is calculated.

Ratio (and difference) values occuring less than THRESHOLd percent as much
as the most frequent value will be excluded from the calculations.  The
default is THRESHOLd = 0.0, that is, to not exclude any values based only on
frequency.

MODE3 may be used to disable filtering.  Typing 'NOFILTER or MODE3=NOFILTER
will prevent the program from performing its normal 5-element, smoothing
box-filter on the histogram.

PERCENT is a real number specifying the desired saturation level (in percent).
Since the mean is pegged at DN=128, and the stretch is linear, only one end
of the histogram will be saturated at this percentage.  The saturation at the
other end will be less.  The default is saturation of 2.0 percent.

MODE4 may be used to disable the normal histogram output.  Set it equal to 
NODISPLA or usr 'NODISPLA.

ATM1 specifies a real number to be added to IN1 before computing ratios or
differences.  This value is normally used as an atmospheric correction term,
and is usually negative.  The default is 0.0.

ATM2 specifies a real number to be added to IN1 before computing ratios or
differences.  This value is normally used as an atmospheric correction term,
and is usually negative.  The default is 0.0.