[mythtv-users] Dirty haze on certain channels

[Joseph Fry]

> >> When recording on the HDHR it works well, except on the CW and
> >> occasionally on Fox, where I see a sort of dirty film over the
> >> picture.  Especially, on the particularly dark scenes.  Its looks like
> >> someone wiped the screen with a dirty cloth leaving a dirty haze.  It
> >> last for a few seconds, disappears, then happens again.  Is there a
> >> name for this phenomenon?  The terms "dirty," "film," and "haze" do
> >> not return much.
> >
> > Ghosting of previous images?  If so, it sounds like someone (CW/Fox or
> > your local broadcaster or your local re-broadcaster (cable co)) is
> > encoding with a bad encoder (or bad encoding options).
> >
>  I am not sure. Its like at some point during the scene, the recorder
> makes a light charcoal rubbing of the scene on transparent paper, then
> removes the paper, waits a few seconds and does it again.  We just
> finished watching two episodes of first season Supernatural that I
> ripped from my DVD, and saw the same effect through MythVideo, if less
> often.
>

I see the exact problem your referring to and I just call it smearing.

Essentially what happens is that at each key frame you get a nice clean
image. Then the subsequent I-frames are either too low bandwidth to maintain
the clarity of the image and/or they use encoding settings that do not
maintain contrast in the dark regions of the image and it starts to degrade.
 It continues to get worse and worse until finally the next key frame comes
along and clears it up.

The good news is, its easy to fix.  The bad news is, there is nothing you
can do to fix it.  This is simply an encoding issue at your cable company.
 They are notorious for compressing video to the point of being unwatchable
so that they can add one more channel of infomercials.

I highly recommend getting a good antenna and pulling you local stations in
OTA (over the air). Broadcasters don't try and shove 10 channels on a single
multiplex like the cable companies do, and they typically put out a much
higher quality signal.

DVD encodes can suffer the same fate if the person encoding the video isn't
careful to prevent it.  Most commonly you would see this in dark scenes
where there is high motion.  Most compression algorithms take advantage of
our limited perception of contrast in very dark regions.  The downside is
that scenes that are mostly dark and depend upon contrast in the dark areas
get muddied up pretty bad.  My bet is that your DVD's were encoded at the
lowest possible bitrate so that they could get the entire season on the
fewest number of disks, it's not surprising that you would see quality
suffer.
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