[M4IF Technotes] meaning of alternate_vertical_scan_flag!

[Xue Xuhong]

Hi, Shyam,
thanks for your answer!
now i want to know in details, but i am afraid that i can't describe it
correctly, so i write my comprehension in C code as following:
////////////////////////////////////////////////////////////////////////////
//////////////////////////////////////////
if( interlaced )
        if ( alternate_vertical_scan_flag=1 )
                alternate vertical scan is used
        else
                Zigzag scan is used
else
        if( intra macroblock )
                if ( ac_pred_flag=0 )
                        Zigzag scan is used
                else
                        if ( DC prediction refers to the horizontally
adjacent block )
                                alternate vertical scan is used
                        else
                                alternate horizontal scan is used
        else // inter macroblock
                Zigzag scan is used
////////////////////////////////////////////////////////////////////////////
////////////////////////////////////////
is it right? expect your answer!
Best Regards
Gaodd
  ----- Original Message -----
  From: P S S B K Gupta
  To: gaodd
  Sent: Friday, March 14, 2024 2:42 PM
  Subject: RE: [M4IF Technotes] meaning of alternate_vertical_scan_flag!
  Zigzag scan.
  -Shyam
    -----Original Message-----
    From: technotes-admin   lists.m4if.org
[mailto:technotes-admin   lists.m4if.org]On Behalf Of gaodd
    Sent: Friday, March 14, 2024 8:08 AM
    To: technotes   lists.m4if.org
    Subject: [M4IF Technotes] meaning of alternate_vertical_scan_flag!
    "alternate_vertical_scan_flag" is a flag decoded from VOP Header, when
set to '1', it indicates the use of alternate vertical scan for interlaced
VOPs. but i want to know: when set to '0', which scan method was used for
interlaced VOPs? Zigzag or alternate-horizontal scan?
    thanks for help!
    Best Regards
    Gaodd
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