[M4IF Technotes] Offscreen MVs

[the_ether]

Yes it was the reference frame I was referring to. So with the result as you
described I would get a macroblock (MB) that is misaligned by 2 rows of
pixels.
If the feature had moved offscreen by (0,-1), in frame 2, without using mpeg
compression, I would see
2
3
4
..
15
So in such a situation it would best to use a MV of (0,0) as I'd only be
wrong by one row of pixels.
Well, I guess it's not such a big problem as it's not that common on
occurrence. the most likely would be camera movement instead of feature
movement at the edge of frame.
----- Original Message -----
From: "Peter Haighton" <Peter.Haighton   m4if.org>
To: "the_ether" <the_ether   btinternet.com>; <technotes   lists.m4if.org>
Sent: Tuesday, May 21, 2024 2:01 AM
Subject: RE: [M4IF Technotes] Offscreen MVs
> Graham,
>
> If I understand you correctly, the values that you are mentioning are
> coming from the reference frame. So by moving the block up by one pixel,
> you would get
>
> 1
> 1
> 2
> 3
> .
> .
> .
> 15
>
> Peter
>
> -----Original Message-----
> From: technotes-admin   lists.m4if.org
> [mailto:technotes-admin   lists.m4if.org]On Behalf Of the_ether
> Sent: Monday, May 20, 2024 5:04 PM
> To: Peter Haighton; technotes   lists.m4if.org
> Subject: Re: [M4IF Technotes] Offscreen MVs
>
>
> Thank you Peter.
>
> > Yes, it is possible for a motion vector to point off the screen. The off
> > screen pixels are duplicated from the edge of the on screen pixels.
>
> Just so I'm absolutely sure I understand, in my example which edge is
> filled?
>
> If I start with the following feature at (0,0):
>
> 1     1    1....1
> 2     2    2....2
> 3     3    3....3
> 16 16 16 ...16
>
> and if this feature moves up by one pixel so that the motion vector is
> (0,-1), what will the 1st and last rows of the corresponding macroblock
> look
> like?
>
> What I want to decribe to the decoder by sending a MV of (0,-1) is that
> the
> first 2 rows should be
>
> 2222...
> 3333...
>
> the fifteenth should be
>
> 16 16 16...
>
> and the last row could be anything.
>
> if instead the first two rows are
>
> 2222...
> 2222...
>
> and the last row
>
> 16 16 16...
>
> then only the first row would be correct. My guess is that the last is the
> behaviour that would occur.
>
>
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