[M4IF Technotes] Question about Quarter-pel Motion Compensation

[Xue Xuhong]

Hi, Gray,
Thank you for your answer.
According to  your explain, we can conclude that:
1) In half-sample mode, the range of MVD should be [-16,16] in full-sample
luma units
2) In quarter-sample mode, the range of MVD should be [-8,8] in full-sample
luma units
Is it right?
Best Regards,
Xue Xuhong
----- Original Message -----
From: "Gary Sullivan" <garysull   microsoft.com>
To: "Xue Xuhong" <xxh   soft.thtf.com.cn>; <technotes   lists.m4if.org>
Sent: Wednesday, January 22, 2024 2:51 PM
Subject: RE: [M4IF Technotes] Question about Quarter-pel Motion Compensation
If I recall correctly (there is no guarantee that I do), the
table is reinterpreted so that what was -16 in full-sample luma units
for half-sample luma motion comp (which is -32 in half-sample luma units
for
half-sample luma motion comp) becomes -8 in full-sample luma units for
quarter-sample luma motion comp (which is -32 in quarter-sample units
for quarter-sample luma motion comp).
Best Regards,
Gary
+> -----Original Message-----
+> From: Xue Xuhong [mailto:xxh   soft.thtf.com.cn]
+> Sent: Tuesday, January 21, 2024 6:55 PM
+> To: technotes   lists.m4if.org
+> Subject: [M4IF Technotes] Question about Quarter-pel Motion
+> Compensation
+>
+>
+> Hi,
+>
+> In the VLC table for MVD( Table B-12,  in the standard) , it
+> seems that the
+> "-16", "-15.5"... are in the unit of pel.
+> which is showed below:
+>
+> Code                      MVD
+> 0000 0000 0010 1       -16
+> 0000 0000 0011 1       -15.5
+> 0000 0000 0101         -15
+> ...
+>
+> When the Quarter-pel Motion Compensation is used, if the codes in the
+> bitstram is 0000 0000 00101, should I consider the MVD as
+> "-16" in pel unit, then transform it to -16*4=-64 in 1/4 pel unit?
+>
+> Thanks a lot.
+>
+>
+> Regards,
+> Xue Xuhong
+>
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+>
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