[x264-devel] Thresholds about slicetype_decide

[kenter]

Hi,
     I'm research on slicetype decide algorithm of x264, It seems that
x264 will perform a low-resolution version of ME and Intra-Pred for
each "MB" (Actually 8x8 for low-res version), and then sum up cost of
each "MB" to get the cost for current slice.
     I feel it may NOT precision as I expect, so, I modify the
algorithm by ME&Intra-pred on origin image instead of the
low-resolution one. Steps are list below:
     1. Calculate half-pel values for origin image
     2. Analyse each MB and sum-up cost(16x16ME instead of 8x8; Intra
analyse also modified as Intra16x16 prediction)
     3. slicetype_decision & cost comparison between references

     I anticipate the PSNR may be more or less improved, however, the
result shows the PSNR DROPs about 0.8dB(from 34.84 drops to 34.06dB)!
I guess it may caused by the thresholds of slicetype_decide and rate
control algorithm, but there are too many thresholds to modulate, is
there anybody can help me on this issue?

    Thanks!