Photoshop

Apply the Trace Contour filter

  1. Choose Filter > Stylize > Trace Contour.
  2. Choose an Edge option to outline areas in the selection: Lower outlines areas where the color values of pixels fall below the specified level, and Upper outlines areas where the color values fall above.
  3. Enter a threshold (Level) for evaluating color values (tonal level), from 0 to 255. Experiment to see what values bring out the best detail in the image.

    Use the Info palette in Grayscale mode to identify a color value that you want traced. Then enter the value in the Level text box.