[Xvid-devel] PSNR, Bitrate of Full Search and other algorithms

[Chien Tran]

Thank you for your answer. The Rate-Distortion Optimization is turned off
completely. I was surprised at the result because in many scientific papers
about motion estimation, they often compare the PSNR and the bit rate with
Full Search algorithm to evaluate the performance of new algorithm. And in
my experiment result with the new algorithm, the UM Hexagon algorithm that
is used in H.264 (and I personally think that this is an quite advanced
algorithm)  also gives quite similar PSNR and bit rate compared with Full
Search, that make me feel unsure about my algorithm because mine is very
simple and much more simpler than the UMHexagon algorithm, but the bitrate
is so different (ex. the Full Search is 526.6 kbits/s, UMhexagon is
526.61kbits/s, and my algorithm is 426.68 kbits/s).

Regards,

2012/6/14 Michael Militzer <michael at xvid.org>

> Hi,
>
> it depends on how your full search is implemented and how you determined
> your test points on the R-D curve (rate-controlled, at constant QP?). You
> didn't mention about this.
>
> In general though, it is not unusual at all that an advanced motion
> estimation algorithm beats a full search strategy. It is well known that
> a naive full search (so simply selecting the match that minimizes a
> simple distortion metric like SAD or SSE) produces highly irregular and
> erratic motion vector fields. A more advanced motion estimation algorithm
> like a predictive search strategy usually produces much smoother motion
> vector fields that better correlate with the underlaying "true" motion,
> can be more effectively predicted and are therefore cheaper to code.
>
> The savings in coding the motion vectors can be so large that an advanced
> motion estimation algorithm produces a lower overall rate than a full
> search approach (like you observed). As to PSNR: Note that PSNR typically
> measures the distortion of the reconstructed pictures. In contrast, SAD or
> SSE that you use during your full search capture the absolute difference
> between the current block and its match in the reference frame (so before
> any reconstruction). The motion vectors that minimize SAD/SSE during motion
> estimation do not necessarily produce reconstructed frames with best PSNR.
>
> Best regards,
> Michael
>
>
> Quoting Chien Tran <chien.study at gmail.com>:
>
> > Hi guys,
> > Sorry if this question make you feel uncomfortable because it is not
> > related to XVID, but more related to Motion Estimation algorithm in video
> > compression. I am implementing new search algorithm that is used in
> motion
> > estimation. The interesting point is that the new algorithm give the
> bigger
> > PSNR and lower bit rate in comparison with Full Search algorithm. I
> tested
> > this new algorithm on different video sequences here
> > http://trace.eas.asu.edu/yuv/ and I still got the same results (bigger
> PSNR
> > and lower bit rate than Full Search). What do you think about this? Is it
> > normal or just a bugs in my algorithm? and do you guys think it is
> possible
> > that sometimes new algorithm can give bigger PSNR and lower bit rate than
> > Full Search algorithm? Has any of you experienced this kind of strange
> > result before?
> > Thanks in advance!
> >
> > --
> > Best wishes,
> >
> > Tran Xuan Chien
> > University of Information Technology
> > Phone: (+84) 1692 468 154
> > _______________________________________________
> > Xvid-devel mailing list
> > Xvid-devel at xvid.org
> > http://list.xvid.org/mailman/listinfo/xvid-devel
> >
> >
>
>
>
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>



-- 
Best wishes,

Tran Xuan Chien
University of Information Technology
Phone: (+84) 1692 468 154