[x264-devel] PSNR vs the distance of reference frame

[Dylan Klebesadel]

The reason for the increace in PSNR is the P.
Think of what the P stands for.

Your ASNR would be the same or lower, however.
Try doing this with the increace to 14 and collecting the ASNR and PSNR
going downwards and plot a graph.
You'll see what I mean :)

Peak Signal to Noise Ratio
Average Signal to Noise Ratio
The latter is more important for compression and the former is more
important for finding how to fix the ladder (when what is going on when it
reaches peak)

Logs please?

On Tue, Jun 29, 2010 at 5:25 PM, john sisi <sisi.john1 at gmail.com> wrote:

> Dear All,
>
> I performed an experiment using x264 to find the effect of using
> different reference frames on the PSNR performance. I got a somehow
> weird result: it seems that the PSNR goes up (by about 0.2dB on
> Foreman CIF @256kbps) as the distance to the reference frame is
> increased (from 3 to 15).
>
> I set the number of reference frame to 15 using "--ref 15" and I
> changed the code such that I was able to select only one of these 15
> reference frames for encoding the frames. For example, in
> "x264_mb_analyse_inter_p16x16" I set "i_ref" to 5 just before
> "REF_COST( 0, i_ref )" to use only the 6th reference frame. I applied
> the same change on the other relevant functions like
> "x264_mb_analyse_inter_p16x8".
>
> My expectection is that the PSNR values must go down as we use farther
> reference frames but is this result reasonable?  Thanks,
> John
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