[x264-devel] Understanding Intra mode prediction

[Son Minh Tran]

Dear All,
I have some questions concerning how x264 selects the prediction mode 
for intra coding
-How did you derive the coefficient i_lambda=pow(2,QP/6-2)?
-For a flag b_fast_intra, I saw that  you  switch it  on  when   the 
block is less likely  in intra mode. And you did nothing when the block 
is likely in intra mode. Here is the extraction from the code:
        /* Fast intra decision */
        if( h->mb.i_mb_xy - h->sh.i_first_mb > 4 )
        {
            if(   IS_INTRA( h->mb.i_mb_type_left )
               || IS_INTRA( h->mb.i_mb_type_top )
               || IS_INTRA( h->mb.i_mb_type_topleft )
               || IS_INTRA( h->mb.i_mb_type_topright )
               || (h->sh.i_type == SLICE_TYPE_P && IS_INTRA( 
h->fref0[0]->mb_type[h->mb.i_mb_xy] ))
               || (h->mb.i_mb_xy - h->sh.i_first_mb < 
3*(h->stat.frame.i_mb_count[I_4x4] + h->stat.frame.i_mb_count[I_8x8] + 
h->stat.frame.i_mb_count[I_16x16])) )
            { /* intra is likely */ }
            else
            {
                a->b_fast_intra = 1;
            }
        }

Or I misunderstood something?
Thank you for any clarification
Son

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