In the system we use for recording and transmitting lectures over the Internet, the board content is transmitted as vector graphics, producing thus a high quality image, while the video of the lecturer is sent as a separate stream. It is easy for the viewer to read the board but the lecturer appears in a separate window. To eliminate this problem, we segment the lecturer from the video stream and paste his image onto the board image at video stream rates. The lecturer can be dimmed from opaque to semitransparent, or even transparent. This paper explains the techniques we apply to achieve this and argue that it can also compete with state of the art image segmentation used for foreground extraction in still images. The approach does not only provide a solution to the divided attention problem which arises when board and lecturer images are transmitted in two different streams, it can also be applied to a variety of other problems where a foreground object must be segmented.
