Triton Isis - Manual (Page 139)

June 2004 Isis® Sonar User's Manual, Volume1 125
8.4 Downsample
In Isis, downsampling techniques can be used to compress many across-track
imagery samples into a single pixel value for display. Such compression permits
displaying a relatively large amount of data in the relatively limited space of a
computer monitor. By carefully choosing an appropriate downsampling technique
to match the type of data to be displayed, you can control the amount and type of
detail you want to see in your imagery. For any given data set, different
downsampling techniques yield different displays of imagery. Yet downsampling
does not modify the underlying data; downsampling merely affects the way your
data is displayed.
Note:
Do not confuse downsampling for display purposes with downsampling
for recording purposes. This section you are reading is limited to
downsampling for display purposes. For a discussion of downsampling
for recording purposes, see 4.3, ‘File Format Setup’.
When you choose a downsampling method (Figure 8-5 shows the downsampling
methods if you choose View→Downsample ), all display windows and hardcopy
output in Isis inherit your downsampling choice. In other words, Isis uses your
chosen type of downsampling everywhere. However, Target and TargetPro are
exceptions to this behavior; neither of those programs are affected by your
downsampling choice because those programs always display each sample in
full resolution.
Increased storage capacity, faster computer processors and modern digital
sonars have made it possible to store more samples of sonar data than ever
before. The more samples you are able to capture and store, the richer and more
detailed the display of your imagery can be. Other benefits of storing these
additional samples include improved across-track mensuration accuracy,
improved spatial resolution in cases of extreme zoom, and more options for
image processing.
Some sonars can generate more than 10,000 samples per channel. When a
side-scan sonar emits 10,000 samples per channel, the number of samples that
must be represented on the screen is 20,000 (10,000 for the port channel and
10,000 for the starboard channel). In an Isis system equipped with just one
monitor, Isis typically displays 1280 pixels across-track; of these, 1000 are
typically used in the waterfall display window. Some Isis systems have four
Chapter 8: Using the View Menu