There are different variants of 3D iso-contouring, which can be selected as illustrated below.
Automatic Variants
The top three entries are automatic procedures starting from the pixel, at which the user is clicking and looking for the largest connected iso-contour passing through the pixel.
•Hot 3D, the area with values above the clicked pixel value is enclosed
•Cold 3D, the area with values below the clicked pixel value is enclosed
•Equal 3D, the area with the clicked pixel value is enclosed (useful for label maps).
Structures are best contoured by clicking at their boundaries, as illustrated below.
Note: With each click in the image, the contour is replaced by a new iso-contour. To get an additional contour please hold down the CTRL keyboard key while clicking.
Interactive Variants
The interactive variants are based on region growing as long as the mouse button is hold down. As for the automatic versions, there are Hot, Cold and Equal variants available. The illustration below shows, how the region is growing radially from the clicking point, including pixels with values ≥ the clicked value. By repeating the interactive growing from different points while holding the CTRL keyboard key, multiple segments can be combined.
Note the variants with holes and without holes. The first one will allow cavities, while they will be filled in the second.