To compensate the deficit of 3D content, 2D to 3D video conversion (2D-to-3D) has recently attracted more
attention from both industrial and academic communities. The semi-automatic 2D-to-3D conversion which
estimates corresponding depth of non-key-frames through key-frames is more desirable owing to its advantage
of balancing labor cost and 3D effects. The location of key-frames plays a role on quality of depth propagation.
This paper proposes a semi-automatic 2D-to-3D scheme with adaptive key-frame selection to keep temporal
continuity more reliable and reduce the depth propagation errors caused by occlusion. The potential key-frames
would be localized in terms of clustered color variation and motion intensity. The distance of key-frame interval
is also taken into account to keep the accumulated propagation errors under control and guarantee minimal user
interaction. Once their depth maps are aligned with user interaction, the non-key-frames depth maps would be
automatically propagated by shifted bilateral filtering. Considering that depth of objects may change due to
the objects motion or camera zoom in/out effect, a bi-directional depth propagation scheme is adopted where a
non-key frame is interpolated from two adjacent key frames. The experimental results show that the proposed
scheme has better performance than existing 2D-to-3D scheme with fixed key-frame interval.