Constant intensity-contours provide an alternate way of displaying the data, replacing the false color display controlled by the color scale and color scheme. Constant intensity contours are drawn at selected intensity levels. The resulting image can be zoomed or written to a file in the normal way.
Clicking on the Contour button switches from Linear or Logarithmic mode to contour mode. The default is a set of logarithmically spaced contour lines. The number of contours, intensity value for each contour, and color of each contour line can be altered in a new window that is opened using the Levels button. The contours will be immediately redrawn if you click the Apply button, assuming that you have already clicked the Contour button--otherwise, the changes will take effect the next time you go into contour mode. If you decide to play with the contour levels and/or colors, keep the following in mind:
  • The program assumes that the intensity levels are in increasing order. Arranging them any other way may lead to unpredictable results.
  • The time to draw the image is approximately proportional to the number of contour lines chosen. You will see a real decrease in performance if you select too many contour lines.
  • Too many contour lines can also make an image too busy.
  • Adjacent contour lines should have very different colors, otherwise you will not be able to figure out where the changes happen.
  • You cannot change the parameters of a contour line whose index is greater than the maximum number of lines to be drawn.
  • The ultimate information of the data is limited by the pixelation. Things may look a little odd at extreme magnification.
  • Low-statistics data will result in very noisy, fractal-looking contour lines, because the contour lines faithfully follow the contours of the data including statistical fluctuations. If you are looking at broad features (which is typically the case if you are using contours at all) consider using the Condense option to bin together pixels, resulting in better statistics but poorer resolution.