yuvdenoise vs. y4mdenoise (was Re: [Mjpeg-users] CVS version of mpeg2enc vs the last 'release')

[Steven B. II <ul...@ya...>]

--- Ray Cole <ray...@ea...> wrote:
> I originally built
> from CVS wanting to try y4mdenoise, but it is just
> too slow for me to use.

yuvdenoise and y4mdenoise, completely separate from
algorithmic differences, have one very important
difference right off the bat.  yuvdenoise analyzes the
new frame in terms of non-overlapping 8x8 blocks. 
y4mdenoise analyzes the new frame in terms of
overlapping 4x2 blocks (for intensity) and 2x2 blocks
(for color), and all matches are flood-filled to
extend them to pixel accuracy before applying them. 
From that point of view, y4mdenoise should be 15x to
60x slower than yuvdenoise, but instead (the last I
heard) it's about 3x slower, despite all the extra
work it's doing.  Keep that in mind when you say it's
slow.

Also, yuvdenoise has an artifact that leaves traces of
previous frames behind in new frames.  You see this
especially in fade-outs, where an afterimage is left
behind in the "blank" screen.  You also see this in
after-movie credits against a black background; the
black left behind by moving credits is a different
color than the black in the rest of the image.

Use yuvdenoise if you want to remove most of the noise
from your video stream.  y4mdenoise is more of an
image-reconstructor than a denoiser, really.  It tends
to make VHS videotapes look like LaserDiscs.  I think
it even has forensic applications, e.g. one could run
security-camera video through it to bring out details
in perpetrators' faces.

I recently got access to a dual-processor machine, and
so now I can implement and test a
multi-processor-aware version of y4mdenoise.  Since it
naturally processes intensity separately from color, I
can do them in parallel; that should be an easy change
to write.  I can also process different parts of the
frame in parallel, but that will be much more
difficult to write.  So if you've got a
multi-processor computer, you may get some relief
soon.

Steven Boswell
ulatekh at yahoo dot com



		
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