[XviD-devel] 3 warp point GME

[Michael Militzer]

Hi,

I don't want to critize your work (but rather the whole MPEG-4 GMC
approach ;-)) but isn't a PSNR increase of about 0.15 dB rather weak?
Especially considering that your test clip was tempete which is a constant
'zoom-out' scene. For more generic clips, the gain from GMC will
supposedly be much smaller (while the speed drop is pretty major).

I have not really a deeper understanding of GME/GMC, so correct me if I'm
wrong but the benefits from GMC are basically limited to reducing motion
vector bits (ok, a good GME could also help to improve the normal block
ME but that's just a nice side-effect). So GMC should be more successful
for very low bitrates while its benefits are small/minor for high-bitrate
conditions, right?

bye,
Michael


Quoting Christoph Lampert <chl at math.uni-bonn.de>:

> 
> Hi,
> 
> I'll commit 3 warp point GME now. It tried to change as little as
> possible, so if there's a bug it's easy to go back. 
> 
> GME is functional (I hope) and I had good results for zooming scenes. 
> It's not optimized for speed, yet. Just a simple gradient decent, but in 
> 6 dimensional parameter space instead of 2 dimensioanl image space, so
> it's a little slow...
> 
> Please test with and without GME, since I had to change some other parts
> as well. I hope I didn't break anything...
> 
> gruel
> 
> P.S. Oh, there are two new files: motion/gmc.c and motion/gmc.h
> I guess someone has to add them to windows project files. 
> 
> -------------------------------------------------
> 
> Tempete CIF 512kbps twopass with different quality levels:
> 
> GMC with 3 point GME:
> fps = 38.92, length = 2497, psnr y = 28.99, u = 33.41, v = 35.63
> fps = 37.12, length = 2502, psnr y = 29.00, u = 33.53, v = 35.79
> fps = 33.12, length = 2480, psnr y = 29.22, u = 33.57, v = 35.85
> fps = 29.90, length = 2478, psnr y = 29.25, u = 33.60, v = 35.87
> 
> no GMC:
> fps = 99.16, length = 2487, psnr y = 28.83, u = 33.11, v = 35.31
> fps = 88.78, length = 2493, psnr y = 28.83, u = 33.22, v = 35.47
> fps = 71.03, length = 2478, psnr y = 29.04, u = 33.31, v = 35.60
> fps = 57.98, length = 2476, psnr y = 29.11, u = 33.35, v = 35.60
> 
> 
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