On Tue, 3 Jun 2003, [EMAIL PROTECTED] wrote:
[argh! "quoting" with whitespace! ahem.]
> The one big problem that I do have with the toolset is that I
> get ghosting in very dark scenes, to the point of making some
> stuff *very* uncomfortable to watch -- like seeing it through
> a heavy, dark fog or something.
>
> I have experienced the same or very similar effects (mainly on the
> chroma channels), but in my case the ghosting is actually in the
> original DV. I hadn't noticed if mpeg2enc made it any worse, but
> yuvdenoise (motion-adaptive denoiser) does when doing aggressive
> chroma filtering. Have you verified that the source DV does not show
> any ghosting?
Sadly, I don't have the DV source to that movie around any longer; it
only occurs very occasionally in things and I don't tend to keep the
source around for long after encoding finishes.
While it could conceivably be enhancing noise that already exists in the
source footage, two things convince me otherwise:
1. the effect is *not* present in the I-frames.
2. the effect is very low quality footage while the rest of the film is
considerably better, including brightly lit scenes.
[...]
> The effect is that any motion in the scene will leave a
> notably brighter patch behind when it moves, for every frame
> before the next I frame.
>
> Are the ghosts any color, or just red and blue?
I have only seen red once, in a "black and white" segment of a colour
film. They tend to be blue-grey or black, although moving bright colours
in, say, a title sequence tend to leave a ghost of themselves behind.
> Until then, though, these images very slowly fade out while
> making it hard to distinguish the actually interesting parts
> of the image.
>
> In my case the chroma "ghost" actually seems to be 1-2 frames behind
> the luma (again, in the DV) so I wrote a utility to delay the luma.
I noticed you discussing that the other day -- my video source is an
analog to DV bridge box converting footage broadcast via analog cable
television, so it's generally pretty good quality.[1]
The film in question was a 1970s Hong Kong picture, though, so it's not
the cleanest material I have ever seen.
> So, is there anything that can be done to improve this? This
> is the one major problem I have with my video encoding
> pipeline at the moment, so I am pretty motivated to try and
> fix it.
>
> I've settled on trying to align the chroma blob as best I can and
> doing mild or no chroma denoising (and heavy luma denoising). Not
> entirely satisfactory, but it looks a lot better at full speed than
> frame-by-frame.
*nod* This does not seem to be the same problem as you experienced with
your camera, although some of the effect is similar.
Daniel
Footnotes:
[1] ...except when the source material has MPEG style artifacts in it.
This happens in the occasional channel title sequence, much to my
amusement when I see it in live TV. :)
--
Altogether, I think we ought to read only books that bite and sting us. If the
book does not shake us awake like a blow to the skull, why bother reading it
in the first place?
-- Franz Kafka, _letter to Oskar Pollak_ January 27, 1904
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