DS9 Users Manual
Table of Contents

Contours

DS9 can create and display contours as an overlay on an image. The Contour Menu is used to create, copy, paste,  and configure contours.

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, smooths 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.