[M4IF Technotes] information regarding halfpel interpolation in the quartersample mode

[Gary Sullivan]

Vinod,
1) The remark about biasing means that if the
   fractional part of the motion vector is positive,
   you need to grab one more column of samples to
   the right or one more row below the samples of
   the block at the location pointed to by the motion vector.
   If that fractional part is negative, you need
   a column to the left or a row above.
   If you need to interpolate to predict a 16x16
   area, you will need 17x17 samples in the reference
   picture.  The same is true for half-pel motion.
2) As reported a few days ago on this reflector, there
   is a problem with the specification of MPEG-4's
   quarter pel motion.  It's too early to predict
   how that will be resolved, but most people seem
   in favor of the method in the reference software.
3) Your remark about trying to calculate eight
   quarter pel positions around an integer pel vector
   gives me the impression that you're talking about
   how do a search in the encoder.  The spec only
   covers how the decoder operates, and the decoder
   doesn't need to do anything that fits that description.
   Again I would point to the reference software if
   you want an illustration of how to design an encoder.
Best Regards,
Gary Sullivan   
+> -----Original Message-----
+> From: Vinod Kumar [mailto:kmr   iis.fhg.de] 
+> Sent: Thursday, October 25, 2023 4:52 AM
+> To: technotes   lists.m4if.org
+> Subject: [M4IF Technotes] information regarding halfpel 
+> interpolation in the quartersample mode
+> 
+> 
+> Hello
+> 	i have a confusion regarding halfpel interpolation in 
+> the quartersample
+> mode. The standard says "a reference block of size 
+> (M+1)x(N+1) biased in
+> the direction of the half or quarter sample position is read from the
+> reconstructed and padded reference VOP." what does biased 
+> hear mean? Do
+> I have to calculate the half pel values 8 times for the 
+> eight adjacent
+> positions around the Integerpel mv? If anybody have any web reference
+> regarding the principle of quarterpel interpolation please do let me
+> know.
+> -- 
+> Vinod
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