Contours
DS9 can create and display contours as an overlay on an image.
The Display Contours menu
is used to display contours. To create, copy, paste, and configure
contours, use the Contour Parameters
menu.
Contour Parameters
When creating a new contour, a dialog box appears, in which the user selects
the number of contour levels, smoothness, and the distribution of the contours.
Contour Levels
Specifies the number of contour levels to be generated. A typical number
is between 1 and 10. Note: large numbers of contours can take a long time
to generate.
Contour Smoothness
Specifies how smooth the contours are. A smoothness level of 1 will evaluate
the contour at each image pixel. A level of 2 will evaluate the contour
at every other pixel. The larger the number, the quicker the contour will
be generated, and the less detail will be available.
Contour Scale
Specifies the distribution of the contour levels. A linear distribution
will have equal spacing between contours, Log and Ln will be weighted
at one end. There are two ways to indicate the contour scale, Use Frame
Scale (automatic) and manual
Use Frame Scale
Use the color scale that the image is currently being displayed in.
Therefor there is a one-to-one match between the image color scale distribution
and the contour levels.
Manual
Manually indicate upper and lower levels and a distribution for the
contour levels. The contours generated will not be matched to the image
color scale distribution.
Contour Method
There are two methods that are available to calculate the contour lines.
The first, FAST, blocks down the image, by the smoothness factor,
before contours are calculated. As a result, the larger the smoothness,
the faster the result.
The second method, BETTER, smoothes the image before calculating
contours. As a result, the larger the smoothness, the slower the result.
Notes for Generating Contours
The algorithm used to generate contours is very basic. It is fine for most
applications, however, some data sets, such as sparse data sets, will have
problems. In this case, do not used a Contour Smoothness value over 4.
In extreme cases, only use a value of 1.