Triton Perspective - Manual (Page 119)

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This window shows two overlapping histograms, one is the original histogram and the other
represents the modified histogram based on the adjustments the user makes here. Options in
the histogram window include:
Window Options: The two square boxes along the bottom of the window act as nodes for
manually adjusting the portion of the spectrum to be displayed. The lower and upper dB
bounds can be set by left-clicking on the node and dragging it while the mouse button is
depressed. When the mouse button is released the color map of the DTM layer in the map
view will automatically update.
Color Legend: The gray histogram is the spread of the actual data. The green is the 'contrast-
stretched' histogram of the data as defined by the user selected min/max range of the data.
The green histogram will be the actual data within the user-defined limits spread out over the
entire graph range (dB).
Auto-Contrast: During the construction of the DTM the program uses the default settings to
improve the initial appearance of the image, program defaults are Bias 0% and Threshold
1%. The threshold setting determines where the upper and lower limits of the histogram are
located, based on the threshold curve. A higher Threshold setting will move the upper and
lower limits closer together. The Bias setting again moves the upper and lower limits closer
together but allows the user to ignore the histogram curve. The defaults of 0% and 1%
therefore should include almost all values in the image with very little clipping. Selecting
‘Compute’ will apply the changes made to the Bias and Threshold to the Histogram.
Reset: Allows the user to return the histogram to the original spread that was set during
creation of the image.
An example of how the histogram options affect the DTM display is shown here.
When the user first opens the Bathymetry Histogram window, the histogram displayed was
designed to span the full range of signals in the DTM. This however can lead to a color
imbalance where much of the DTM appears the same color. Shown on the following page is
an example of this, showing the default histogram for a DTM and the resulting color
distribution.