[Mp4-tech] [mp4_tech]:quick question about H.264 ColPic

[David Wu]

Hello Experts,
I have some difficulty understanding the following statement in H.264 Spec.
Please shed some light on this for me.
8.4.1.2.3 Derivation process for temporal direct luma motion vector and reference index prediction mode
- Otherwise, if vertMvScale is equal to Frm_To_Fld, the following applies.
    - If field_pic_flag is equal to 0, let refIdxL0Frm be the lowest valued reference index in the current reference
       picture list RefPicList0 that references refPicCol. MapColToList0( refIdxCol ) returns the reference index
       ( refIdxL0Frm << 1 ). RefPicList0 shall contain refPicCol.
In the statement above, Frm_To_Fld indicates, correct me if I am wrong, that the current picture is a field picture;
why is that we need to check "If field_pic_flag is equal to 0", shouldn't it be 1 in this case if the current picture is a
field picture (due to Frm_To_Fld)
Thanks in advance
David Wu
david_t_wu hotmail.com
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