[XviD-devel] help me please (about setedges() and others)

[Nicola Bicocchi]

On Fri, 31 Oct 2003 18:39:42 +0100 (CET)
Christoph Lampert <chl at math.uni-bonn.de> wrote:

> On Fri, 31 Oct 2003, Nicola Bicocchi wrote:
> 
> > On Thu, 30 Oct 2003 08:08:18 +0100 (CET)
> > Christoph Lampert <chl at math.uni-bonn.de> wrote:
> > 
> > > On Wed, 29 Oct 2003, Nicola Bicocchi wrote:
> > > >   i'm playing with xvid in my thesis and i don't understand some things:
> > > 
> > > Hi,
> > > what's the thesis about? 
> > 
> > A research group of my univeristy have written some code which 
> > recognizes, classifies and tracks moving objects in a scene, and
> > automatically recognizes background changes whenever an object
> > becomes static.
> > The idea is to store (or send) not the whole scene but only
> > interesting objects.
> > Since there are no core profile implementations avaiable, I
> > decided to modify xvid to reach the goal.
> > I've already written a program, but it doesn't reach
> > psnr/bitrate rate values that i was attending for.
> > 
> > I've a couple of other questions.
> > could you breifly explain me what are refH refV refHV,
> 
> Usually (in halfpel mode), noninteger (=halfpel) position are interpolated
> linearly from the integer pixel positions. 
> Instead of interpolating every 16x16 block which each 16x16 macroblock
> might be compared with, XVID interpolated the full frame of these half-pel
> position into a new frame. Since there are 3 possibilites for this: 
> horizontal interpolation, vertical interpolation and interpolation in both
> directions, we have 3 additional reference frame. 
> 
> So, "ref" is the pixel values at positions 
> (0,0), (1,0), (2,0)
> (0,1), (1,1), (2,1),
> (0,2), etc.
> 
> and   refH is the pixel values at 
> (0.5, 0), (1.5, 0), (2.5, 0)
> (0.5, 1), (1,5, 1), ...
> 
> refV is
> (0, 0.5), (1, 0.5), ...
> (0, 1.5), (1, 1,5), ...
> 
> and refHV is
> (0.5, 0.5), (1.5, 0.5), ...
> (1.5, 0.5), (1.5, 1.5), ...
> 
> 
> > and whait is acdc_prediction in I-frames??
> 
> The 0th DCT coefficient (so it's just the mean value of the block) is
> called DC coefficient. All other DCT-coefficients are called AC.
> 
> AC and DC prediction are a way of spacial prediction in I-frames: Since
> usually in neighbouring blocks DCT coefficients are similar, you can
> "predict" some AC coefficients from the top neighbour or left neighbour
> (you subtract them before writing the bitstream).  If that doesn't sound
> promising, you can also just subtract previous DC value from present.
> 
> But if you work on MPEG-4, you should really buy a copy of the standard,
> it's all in there ;-)

where i can buy it ?? and how much does it cost ??
thank you in advance
Nicola



> 
> gruel
> 
> 
> _______________________________________________
> XviD-devel mailing list
> XviD-devel at xvid.org
> http://list.xvid.org/mailman/listinfo/xvid-devel