Triton Isis - Manual (Page 143)

June 2004 Isis® Sonar User's Manual, Volume1 129
Min Of the 20 samples, Isis takes
the minimum value to display. In
the case of 16-bit data, the
minimum magnitude (value least
from zero) is displayed to
preserve the signing of the data. The Min downsample method is
useful when looking only for shadows
when there is a lot of background
noise or clutter. However, strong
returns will be de-emphasized. Use
of this technique is not generally
recommended. Min is the second
fastest downsample method.
Min/Max Of the 20 samples, the one that
is displayed is that which is
farthest away in magnitude from
the local average. The “local
average” is computed to be the
average of a series of samples
around the 20 in question,
extending for 1/30 of the total
ping left and 1/30 right.
The Min/Max technique tends to
make the image look like too much
contrast. This has the effect of
enhancing whatever kind of feature is
present in the image, whether or not
it is a strong sonar return or weak
sonar return. Even so, Min/Max
downsampling is appropriate when
both echoes and shadows must be
viewable on the display. Min/Max is
the second slowest downsampling
method. (However, when 8-bit data
are being downsampled, Min/Max is
slower than RMS.)
Skip Of the 20 samples, the first
sample is displayed and the
remaining 19 are ignored. Skip usually is not desirable because
it degrades the image quality, but it is
the fastest downsampling technique.
Since seafloor features can be
completely eliminated from the
display, use of this technique is not
recommended.
Chapter 8: Using the View Menu