Video segmentation methods and systems are described wherein scene images of subjects and background are captured by video and are automatically segmented according to subject content, as by system determination of the nature of subjects. Segmentation transformations of an original background and foreground images in the scenes are provided as a terrain map. Automatic segmentation threshold adaptation is based on measuring the segmentation noise while holding the number count of noise blobs constant, whereby to achieve noise-adaptive segmentation gain. Automatic threshold adaptation within multiple areas of the scene results in different possible thresholds in different areas based on the amount of segmentation noise in each area. Segmentation is improved accordingly.