The Contour Plot command draws one or more
intensity contours on an image. The contour plotting commands
operate from the Contour Plot Toolbar. Contours are
generated at specified levels. The related
Interactive Contour Plot command allows you to
mark the level where a single contour is to be created. Contouring
can be done on the entire image or within the rectangular region of
interest ("ROI") specified by the
image cursor. Generally, it is best to contour within
the cursor rectangle. To move and resize the cursor, use
Ctrl+A to toggle cursor mode on and
off.
Use the toolbar button (see
below) to control the contours by setting
Contour Plot Properties such as level values
and colors.
Open the Contour Plot Toolbar from the
Plot > Contour Plot Toolbar command in the image menu or
the button on the
Image Plot Toolbar.
Toolbar Commands
The Contour Plot Toolbar controls the
process for drawing contours on an image. This toolbar is opened
from the top-level
Image Plot Toolbar or the Plot > Contour Toolbar menu command.
Procedure
Open the Contour Plot dialog by clicking
the button on the
Image Plot Toolbar. The first time, this opens the
Contour Plot dialog where the properties are set.
In the Contour Plot dialog, set the
properties, then click [Plot] to
generate the contours. Click [Close]
to close the dialog. There are two strategies for defining the
contour levels:
Specify a contour Description on the left side of the dialog, then
click [Copy to Levels >>], or
Enter contour levels you want to use into the
fields on the right side of the dialog.
When you close the Contour Plot dialog the first time, the
Contour Plot Toolbar appear at the edge of the Image
window.
To close the Contour Plot Toolbar, click the button again on the
Image Plot Toolbar.
After plotting contours, you can delete each one separately in
"Delete Mode" by clicking the button
on the Contour Plot Toolbar. In this mode, you point at and
click on the target contour drawn on the image. Alternatively, all
contours will be erased when you close the Contour Plot Toolbar as
in step 4. You can delete all contours using the button.
Remarks
Contour drawing is a CPU-intensive task when
there are a great many contour segments. Generally, it is best to
contour within the cursor rectangle to avoid unnecessary contour
drawing.
Be careful to set contour levels above the
background noise to avoid contouring the noise, which can cause
Mira to appear to lock-up while it creates a great many contour
segments. You can prevent this by selecting a small rectangle for
contouring near the noise level and by limiting the number of
levels to only those you need.
To change the contour levels, colors, smoothing,
or other properties, repeat the above procedure, beginning at step
2.
To reopen the Contour Plot Properties Plot
dialog, click the button on the
Contour Plot Toolbar.
To change the contour line thickness and other
properties, open the
Contour Drawing Properties dialog using the
button on the Contour Plot
toolbar.
A contour consists of a series of line segments.
To export all contour line segments to a file for external
analysis, use the (Export) button at
the bottom of the Contour Plot Toolbar.
Tip
It is usually advisable to use the
Image Cursor to constrain the contouring to the
minimum necessary rectangle. Contours require drawing many short
lines, and a complex contour containing a huge number of line
segments may cause the computer to lag when redrawing the
window.
With many complex contours visible, display
updating is sluggish. You can see this when you adjust the palette
or move the image cursor. To cure that problem, simplify the
contours, increase smoothing, shrink the contour region, or delete
the contour using the (delete all)
button on the contour toolbar.
Contouring Regions of High Noise Level
Below is shown a magnified view of the image above
with a single contour having many wiggles. This contour was created
using Smoothing = low, which creates
many wiggles as the contour tracks through noisy, low level pixels.
For more information about contour plotting in noisy areas of an
image, see
Contour Plot Smoothing.
Tip
You can terminate the contour computation at any
time by hitting the [Esc]key. This is
especially handy if you start a contour computation after
accidentally clicking on a level too far into the noise.
Contour
Plot
button
on the Contour Plot Toolbar. In this mode, you point at and
click on the target contour drawn on the image. Alternatively, all
contours will be erased when you close the Contour Plot Toolbar as
in step 4. You can delete all contours using the 
button.
button on the Contour Plot
toolbar.
(Export) button at
the bottom of the Contour Plot Toolbar.
