D. T. Hoang,
P. M. Long and J. S. Vitter. Efficient cost measures for motion
compensation at low bit rates. IEEE
Transactions on Circuits and Systems for Video Technology,
8(4):488-500, 1998.
Abstract
We present and compare methods for choosing
motion vectors for block-based motion-compensated video
coding. The primary focus is on videophone and videoconferencing
applications, where low bit rates are necessary,
where motion is usually limited, and where the amount
of computation is also limited. In a typical block-based
motion-compensated video coding system, motion vectors
are transmitted along with a lossy encoding of the residuals.
As the bit rate decreases, the proportion required
to transmit the motion vectors increases. We provide experimental
evidence that choosing motion vectors explicitly
to minimize rate (including motion vector coding), subject
to implicit constraints on distortion, yields better rate-distortion
tradeoffs than minimizing some measure of prediction
error. Minimizing a combination of rate and distortion
yields further improvements. Although these explicit-minimization
schemes are computationally intensive, they
provide invaluable insight which we use to develop practical
algorithms. We show that minimizing a simple heuristic
function of the prediction error and the motion vector codelength
results in rate-distortion performance comparable to
explicit-minimization schemes while being computationally
feasible. Experimental results are provided for coders that
operate within the H.261 standard.