[M4IF Technotes] GMC

[Kasturi Rangam]

Thanks for the information. I was wondering if we could calculate
the motion vector range based on du[i] and dv[i] range. Of course
if this range is more than the reference frame, then there is no
point.
--Kasturi
"Sorin C. Cismas" wrote:
> 
> I don't think there are any restrictions on the motion vectors.  I have
> the same concern about the need to fetch 64 non-contiguous 2x2 pels
> to predict a macroblock.  To reduce complexity and bandwidth requirements,
> it is highly desirable to put some limits on du[i] and dv[i] for i>0.
> 
> 2 and 3 warping points are usefull for zoom-in and zoom-out, however, it is
> not realistic to assume, for example, a 10x zoom-out on an S(GMC) prediction.
> A 50% or even 25% zoom-out restriction will be more than sufficient.
> For 50%, this will translate to du[i]<W    and dv[i]<H    for i>0.
> For 25%, this will translate to du[i]<W//2 and dv[i]<H//2 for i>0.
> The 50% restriction will limit the macroblock luma prediction to 25x25.
> The 25% restriction will limit the macroblock luma prediction to 21x21.
> 
> Can these or similar restrictions be considered for a future corrigendum?
> 
> Thanks,
> Sorin Cismas
> 
> > -----Original Message-----
> > From: technotes-admin   lists.m4if.org
> > [mailto:technotes-admin   lists.m4if.org]On Behalf Of Kasturi Rangam
> > Sent: Friday, May 10, 2024 2:46 PM
> > To: technotes   lists.m4if.org
> > Subject: [M4IF Technotes] GMC
> >
> >
> > I am trying to under GMC in MPEG4.
> > Looks like you can have 0, 1, 2 or 3 sprite_warping_points.
> >
> > To decode a 0 and 1 sprite_warping_points macroblock, you can
> > fetch the whole macroblock data from the reference to do pixel
> > prediction.
> >
> > However, for 2 and 3 warping_points, the motion vector for each
> > pixel can be anywhere in the reference frame. Thus we might need
> > to perform 64 data fetches to predict one macroblock.
> >
> > Is there a range that can be calculated for each macroblock, so that
> > we can fetch data only once?
> >
> > Thanks,
> >
> > Kasturi
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