qccvidmeshmotionestimationsearch.3

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.TH QCCVIDMESHMOTIONESTIMATIONSEARCH 3 "QCCPACK" ""
.SH NAME
QccVIDMeshMotionEstimationWarpMesh,
QccVIDMeshMotionEstimationSearch,
QccVIDMeshMotionEstimationCreateCompensatedFrame
\- routines for motion estimation and compensation
using regular triangle meshes
.SH SYNOPSIS
.B #include "libQccPack.h"
.sp
.BI "int QccVIDMeshMotionEstimationWarpMesh(const QccRegularMesh *" reference_mesh ", QccRegularMesh *" current_mesh ", const QccIMGImageComponent *" motion_vectors_horizontal ", const QccIMGImageComponent *" motion_vectors_vertical );
.br
.sp
.BI "int QccVIDMeshMotionEstimationSearch(const QccIMGImageComponent *" current_frame ", QccRegularMesh *" current_mesh ", const QccIMGImageComponent *" reference_frame ", const QccRegularMesh *" reference_mesh ", QccIMGImageComponent *" motion_vectors_horizontal ", QccIMGImageComponent *" motion_vectors_vertical ", int " block_size ", int " window_size ", int " subpixel_accuracy ", int " constrained_boundary ", int " exponential_kernel );
.br
.sp
.BI "int QccVIDMeshMotionEstimationCreateCompensatedFrame(QccIMGImageComponent *" motion_compensated_frame ", const QccRegularMesh *" current_mesh ", const QccIMGImageComponent *" reference_frame ", const QccRegularMesh *" reference_mesh ", int " subpixel_accuracy );
.SH DESCRIPTION
.BR QccVIDMeshMotionEstimationSearch()
and
.BR QccVIDMeshMotionEstimationCreateCompensatedFrame()
perform motion estimation and compensation, respectively,
between two video frames using a regular triangle mesh
rather than square blocks as in the ubiquitous block-based
motion estimation/compensation (i.e., see
.BR QccVIDMotionEstimationFullSearch (3)).
This regular triangle mesh is created by dividing the reference
frame into square blocks and then splitting each block along its diagonal.
.LP
For motion estimation via
.BR QccVIDMeshMotionEstimationSearch() ,
the triangle vertices, or "control points," of the regular mesh are
tracked from the reference frame to the current frame via a
simple, block-based motion-estimation strategy due to Eckert
.IR "et al" .
In this approach, motion into the current frame is estimated by
centering a small block at each vertex in the
reference-frame mesh and finding the best-matching block
in the current frame.
.LP
Once motion is estimated in this manner
and a field of motion vectors determined,
.BR QccVIDMeshMotionEstimationWarpMesh()
can be used to create a motion-compensated version of the
mesh in the current frame from the mesh
in the reference frame. In essence,
.BR QccVIDMeshMotionEstimationWarpMesh()
"warps" the reference-frame mesh into the current frame
by adding to each vertex of the mesh
its corresponding motion vector.
.LP
Once the motion-compensated mesh is available in the current frame,
.BR QccVIDMeshMotionEstimationCreateCompensatedFrame()
can be used to perform motion compensation between the frames.
That is,
.BR QccVIDMeshMotionEstimationCreateCompensatedFrame()
uses affine transforms between the two meshes
to construct a motion-compensated prediction of the current frame from the
reference frame. This motion-compensated frame is constructed by
creating, for each triangle in the reference-frame mesh,
an affine transform that maps the triangle into the current-frame mesh.
This affine transform is then used to map
the pixels corresponding to the triangle
in the reference frame into the current frame,
with bilinear interpolation between
the surrounding four integer-pixel locations used to resolve
subpixel positions produced by the affine mapping.
.SS "Motion Estimation"
.BR QccVIDMeshMotionEstimationSearch()
performs a motion-estimation search to produce a motion-vector field
between
.I reference_frame
and
.IR current_frame .
.IR reference_mesh
is the regular mesh in the reference frame, and
.BR QccVIDMeshMotionEstimationSearch()
estimates the motion of the
vertices of this mesh, producing a motion-vector field
which is returned in
.I motion_vectors_horizontal
and
.IR motion_vectors_vertical .
.BR QccVIDMeshMotionEstimationSearch()
calls
.BR QccVIDMeshMotionEstimationWarpMesh()
(see below)
to produce the corresponding motion-compensated mesh in the current frame,
which is returned as
.IR current_mesh .
.LP
.IR block_size
gives the the size of the square block that is centered at each
mesh vertex in order to determine the vertex motion, following
the block-based vertex-motion estimation procedure outlined by Eckert
.IR "et al" .
.LP
.IR window_size
gives the size of the motion-estimation search window about the current
vertex location.
.LP
.I subpixel_accuracy
is one of
.BR QCCVID_ME_FULLPIXEL ,
.BR QCCVID_ME_HALFPIXEL ,
.BR QCCVID_ME_QUARTERPIXEL ,
or 
.BR QCCVID_ME_EIGHTHPIXEL ,
indicating full-, half-, quarter-, or eighth-pixel accuracy.
If anything other than integer-pixel accuracy is used,
.BR QccVIDMotionEstimationCreateReferenceFrame (3)
must be called on both
.IR current_frame
and
.IR reference_frame
to interpolate them to the appropriate subpixel accuracy
prior to calling
.BR QccVIDMeshMotionEstimationSearch() .
.LP
If
.IR constrained_boundary
is 1, 
.BR QccVIDMeshMotionEstimationSearch() 
constrains all vertices that lie on the boundary of the reference frame
to have zero-valued motion vectors. In doing so, the resulting
.IR current_mesh
is guaranteed to cover the entire
.IR current_frame
with no "gaps."
If
.IR constrained_boundary
is 0, no such guarantee is in place, and motion vectors for the image-boundary
vertices can take on any value, perhaps moving into the interior of
the image or beyond the
bounds of the image.
This latter, unconstrained approach
may permit better motion estimation at the
expense of some "gaps" possibly arising in the
corresponding motion-compensated frame.
.LP
If
.IR exponential_kernel
is 1,
a exponential function is used to create a kernel for the block-based
search process that estimates the motion of the mesh vertices. This
exponential kernel provides greater weight to the pixels in the
center of the block (i.e., corresponding to the vertex of interest itself) and
exponentially decreasing weight to pixels distant from the center.
If
.IR exponential_kernel
is 0, all pixels in the block are weighted the same in the motion-estimation
search. See Eckert
.IR "et al" .
and Schroder and Mech.
.SS "Motion Compensation"
.BR QccVIDMeshMotionEstimationCreateCompensatedFrame()
constructs the motion-compensated prediction of
the current frame from
.I reference_frame
using affine transforms between the reference-frame mesh,
.IR reference_mesh ,
and the current-frame mesh,
.IR current_mesh .
The motion-compensated frame is returned in
.IR motion_compensated_frame ,
which must be allocated prior to calling
.BR QccVIDMeshMotionEstimationCreateCompensatedFrame() .
.LP
.IR subpixel_accuracy
is one of
.BR QCCVID_ME_FULLPIXEL ,
.BR QCCVID_ME_HALFPIXEL ,
.BR QCCVID_ME_QUARTERPIXEL ,
or 
.BR QCCVID_ME_EIGHTHPIXEL ,
indicating full-, half-, quarter-, or eighth-pixel accuracy.
If anything other than integer-pixel accuracy is used,
.BR QccVIDMotionEstimationCreateReferenceFrame (3)
must be called on
.IR reference_frame
to interpolate it to the appropriate subpixel accuracy
prior to calling
.BR QccVIDMeshMotionEstimationCreateCompensatedFrame() .
On the other hand,
.IR motion_compensated_frame 
must be the same size as the original current and reference frames
in all cases (i.e., it is not interpolated to subpixel accuracy).
.LP
.BR QccVIDMeshMotionEstimationCreateCompensatedFrame() 
uses
.BR QccTriangleCreateAffineTransform (3)
to construct an affine transform between each pair of
reference-frame and current-frame triangles, and
.BR QccPointAffineTransform (3)
to map a pixel from the reference frame to the current frame.
.SS "Mesh Warping"
.BR QccVIDMeshMotionEstimationWarpMesh()
constructs a mesh in the current frame,
.IR current_mesh ,
from a mesh in the reference frame,
.IR reference_mesh ,
by adding motion vectors to each vertex of
.IR reference_mesh .
The motion vectors are specified by
.IR motion_vectors_horizontal
and
.IR motion_vectors_vertical
and are usually obtained via
.BR QccVIDMeshMotionEstimationSearch() .
.IR current_mesh
must be allocated to the same size as
.IR reference_mesh
prior to calling
.BR QccVIDMeshMotionEstimationWarpMesh() .
.SH "RETURN VALUE"
These routines return 0 on success, and 1 on failure.
.SH "SEE ALSO"
.BR QccVIDMotionVectorsEncode (3),
.BR QccVIDMotionVectorsDecode (3),
.BR QccRegularMesh (3),
.BR mesh_memc (1),
.BR QccPackVID (3),
.BR QccPackENT (3),
.BR QccPack (3)

Y. Altunbasak, A. M. Tekalp, and G. Bozdagi,
"Two-Dimensional Object-based Coding Using a Content-based Mesh
and Affine Motion Parameterization," in
.IR "Proceedings of the International Conference on Image Processing" ,
Washington, DC, October 1995, vol. 2, pp. 394-397.

M. Eckert, D. Ruiz, J. I. Ronda, and N. Garcia,
"Evaluation of DWT and DCT for Irregular Mesh-based
Motion Compensation in Predictive Video Coding,"  in
.IR "Visual Communications and Image Processing" ,
K. N. Ngan, T. Sikora, and M.-T. Sun, Eds., Proc. SPIE 4067,
June 2000, pp. 447-456.

K. Schroder and R. Mech,
"Combined Description of Shape and Motion in an Object
Based Coding Scheme Using Curved Triangles," in
.IR "Proceedings of the International Conference on Image Processing" ,
Washington, DC, October 1995, vol. 2, pp. 390-393.

Y. Wang, S. Cui, and J. E. Fowler,
"3D Video Coding Using Redundant-Wavelet Multihypothesis and
Motion-Compensated Temporal Filtering," in
.IR "Proceedings of the International Conference on Image Processing" ,
Barcelona, Spain, September 2003, vol. 2, pp. 755-758.

Y. Wang, S. Cui, and J. E. Fowler,
"3D Video Coding with Redundant-Wavelet Multihypothesis,"
.IR "IEEE Transactions on Circuits and Systems for Video Technology" ,
submitted July 2003. Revised April 2004, March 2005.

.SH AUTHOR
Copyright (C) 1997-2007  James E. Fowler
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