[M4IF Technotes] question about intra_dc_vlc_thr2

[Gaurav Aggarwal]

Kosuge-san,
Thanks. I will just modify your pseudo-code a little since I believe
it doesn't cover everything but yes, it does summarize everything
very clearly. 
If(Intra AC VLC is turned on || inter) {  // change made by me!!
   if(pattern_code == 1) {
	this case coeff without distinction of ac or dc.
	MB has 64 coeff. And they are derived from Tbl.B-16 or Tbl.B-17.
	<first(dc) coeff && last = 1  case exist>
   }
   else { //(pattern_code == 0) 
	64 coeff are all 0.
   }
}
else { //Intra AC VLC is turned off
   if(pattern_code == 1) {
	MB has 64 coeff(1 dc_coeff and 63 ac_coeff).
	dc_coeff is derived from Tbl.B13-Tbl.B15.
	ac_coeff are derived from Tbl.B-16 or Tbl.B-17.	
   }
   else { //(pattern_code == 0) // change made by me!!
	dc_coeff is derived from Tbl.B13-Tbl.B15.
	ac_coeff(63 coeff) are all 0.
   }
}
Gaurav
> -----Original Message-----
> From: tetsuo kosuge [mailto:kosuge   td.idc.lsi.sanyo.co.jp]
> Sent: Wednesday, March 05, 2024 1:44 PM
> To: Gaurav Aggarwal
> Cc: Technotes   lists.m4if.org
> Subject: Re: [M4IF Technotes] question about intra_dc_vlc_thr2
> 
> 
> Sorry, I fogot to write distiction of Intra or Inter.
> 
> Hi Mr.Aggarwal.
> 
> That's my previous question,so I have no confidence.
> But I understand as follows(Mr.Gautam's answer is helpful me to 
> understand) :
> 
> ------------------------------------------------------------------
> -----------
> 
> If(Intra AC VLC is turned on) {
> 	if(pattern_code == 1) {
> 		this case coeff without distinction of ac or dc.
> 		MB has 64 coeff. And they are derived from Tbl.B-16 
> or Tbl.B-17.
> 		<first(dc) coeff && last = 1  case exist>
> 	}
> 	else { //(pattern_code == 0) 
> 		64 coeff are all 0.
> 	}
> }
> else { //Intra AC VLC is turned off
> 	if(pattern_code == 1) {
> 		MB has 64 coeff(1 dc_coeff and 63 ac_coeff).
> 		dc_coeff is derived from Tbl.B13-Tbl.B15.
> 		ac_coeff are derived from Tbl.B-16 or Tbl.B-17.	
> 	}
> 	else if(Intra_MB){ //(pattern_code == 0)&&Intra 
> 		dc_coeff is derived from Tbl.B13-Tbl.B15.
> 		ac_coeff(63 coeff) are all 0.
> 	}
> 	else {  //(pattern_code == 0)&&Inter
> 		64 coeff are all 0.
> 	}
> }
> 
> ------------------------------------------------------------------
> ---------------
> Regards,
>  Tetsuo
> 
> 
> >For an Intra block with Intra AC VLC turned on, suppose there was
> >only 1 DCT coefficient, then is it correct to say that the decode
> >of the first VLC DCT coefficient will give out a LAST==1? 
> >
> >Or lets say that Intra AC VLC is turned on and cbpy[] for an intra
> >block is 0. Then it means that there is no DCT coefficient at all
> >for this block. Neither DC nor AC.
> >
> >And to understand this completely, if the Intra AC VLC is turned 
> >off for the block and there is only 1 DCT coefficient, it means
> >that only DC coefficient is present. Hence, the cbpy[] for this
> >block will be '0' since there are no AC coefficients. Correct?
> >
> >Gaurav
> 
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