Log offset
For log scale type, the offset is in decibels at the left edge or
lower edge of the display. The histogram is plotted according to the
following formula.
dB
=
20
log
X
peak
,
where
•
X is the number of hits per column for horizontal histograms, or the
number of hits per row for vertical histograms.
•
Peak is the number of hits in the peak.
•
dB is the log value that gets plotted.
This means that 0 dB is at the peak of the histogram and that the offset can
only contain negative values. For example, with a horizontal histogram, an
offset of
−
20 dB places 10% or 10
(
−
20/20)
of the peak at the lower edge of the
display.
Scale Mode
The scale mode softkey determines how much of the histogram is displayed
on the screen. If the axis softkey is set to horizontal, auto sets the base of the
histogram to the bottom of the graticule area and displays the histogram
using half of the graticule height. If the axis softkey is set to vertical, auto
sets the base of the histogram to the left edge of the graticule area and
displays the histogram using half of the graticule width.
Manual lets you window in on the histogram by allowing you to change the
scale and offset settings. Depending on the setting of the scale type softkey,
the scale value is in either percent of peak per division or dB. By changing
the scale, you can zoom in or out on the histogram. Offset allows you to pan
across the histogram by moving the base of the histogram. Depending on the
setting of the scale type softkey, the offset value is also in either percent of
peak or dB per division.
Histogram Menu
Histogram Scale
24–9
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