[MEncoder-users] hqdn3d versus lavc's nr

[Phil Ehrens]

Jean Hoderd wrote:
> Hi,
> 
> There seem to be two ways of applying a denoise filter
> if one is using lavc: one in the video filter chain,
> with hqdn3d; the other with the nr option in lavcopts.
> 
> Now, how do these compare exactly, and which one is
> recommended for a high quality encoding?  (And with
> which settings?)

hqdn3d is a traditional temporal denoiser. nr is what
is commonly referred to in signal processing as decimation
(understood to mean, more specifically, decimation with
filtering). I am basing this analysis on the observed
effect on bitrate. I have not been interested enough to
look at the code. Maybe my analysis is inaccurate.

I use hqdn3d for denoising. The default values are good for
animation, but for live action I prefer something like
3:2:3:3. File size decreases quite a bit when hqdn3d is used,
and if it is used judiciously it can really improve the
appearance of material intended to be burned to dvd for playing
on commercial players. Using excessive values produces noticeable
softening of the picture (hair and textured clothing lose their
detail). The noisier the source (up to a point!) the better it
will respond to hqdn3d. There has to be sufficient signal to
noise ratio in the source or you just get gumbo.

I use nr for file size adjustment. values around 600 can
be used to reduce file size 10-20 percent. Increasing
the value of nr tends to produce a washed-out appearance.
nr reduces the average bitrate and peak bitrate proportionately.
If you encode something and the average bitrate seems excessive,
you can tweak it down with nr (to reduce file size).
Animation is much more forgiving to large nr values than live
action is!!

hqdn3d and nr can be successfully used in combination. Animation
ripped from VHS can benefit from using them together.