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

[Michael Militzer]

Hi,

20% smaller bitrate at higher PSNR only from using a new ME algorithm
doesn't sound right. Are you sure you've measured your PSNR right? Or
that you're not comparing apples with oranges (like: your new algorithm
does subpel refinement but the full search / hexagon search you compare
it to is limited to fullpel precision only)?

Best regards,
Michael


Quoting Chien Tran <chien.study at gmail.com>:

> 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
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