Humminbird 161 Operation Manual page 18

Inverse is a method where weak returns are shown
with dark pixels and strong returns with lighter
pixels. This has the benefit of ensuring that weak
signals will be clearly visible on the display.
Structure ID® represents weak returns as light pixels
and strong returns as dark pixels. This has the
benefit of ensuring that strong returns will be clearly
visible on the display.
WhiteLine® highlights the strongest sonar returns in
white, resulting in a distinctive outline. This has the
benefit of clearly defining the bottom on the display.
Bottom Black displays all pixels below the bottom
contour as black, regardless of signal strength. This
has the benefit of providing a high contrast between
the bottom and other sonar returns on the display.
Any targets such as fish, structure and thermoclines
will be shown using the Structure ID® method.
11