Wavelet based Video coding with optical flow for motion compensation
In broadcasting environments intra-only video coding with JPEG 2000 has shown
to provide many desired features along with high picture quality. However, there
is no exploitation of temporal redundancy, which can reduce the bit rate while
maintaining the quality.
Optical flow algorithms are designed to find the apparent movement of brightness in
an image, and can be used to estimate the motion of each pixel between consecutive
images. This thesis explores the performance of a hybrid video codec that uses the
Classic+NL optical flow algorithm for motion compensation and JPEG 2000
for encoding the estimation error.
The motion estimation proved to be inaccurate at the edges of objects. This can
cause high frequency components in the residue image, which will decrease the
efficiency of JPEG 2000. Occluded regions will also have poor estimation, as they
are not present in the previous frame. Since noise is not considered when the optical
flow is calculated, the energy of the noise may increase after motion compensation.
Without addressing these issues, optical flow algorithms are not well suited for
motion estimation in hybrid video codecs.
Even with the inaccurate motion compensation performed by the optical flow algorithm,
there was an overall reduction in bit rate of 18.8%, compared to intra-only
coding with JPEG 2000. The performance was highly content dependent, ranging
from a reduction of 90% to an increase of 27%. The reduction comes at a cost of
increased delay, higher complexity, vulerability to transmission errors, and a lack
of a constant bit stream. The proposed hybrid codec is therefore not suited to
replace intra-only coding with JPEG 2000 in contribution environments.
Place, publisher, year, edition, pages
Institutt for elektronikk og telekommunikasjon , 2011. , 103 p.
ntnudaim:6211, MTEL elektronikk, Digital kommunikasjon
IdentifiersURN: urn:nbn:no:ntnu:diva-14175Local ID: ntnudaim:6211OAI: oai:DiVA.org:ntnu-14175DiVA: diva2:448152
Perkis, Andrew, ProfessorStephansen, Helge