Green snow

I just saw some quicktimes from a guy who is having trouble with artifacting on transitions and .. I can only describe it as a very light 'green snow' on his rendered footage.

He is using both DV and DVCpro in the same timeline, but I'm not sure why this is affecting rendered footage from either camp.

Has anyone seen anything like this before?

Does it look likeirregular digital blocks?
Or is it constant like fractal noise?

It seemed to be very small blocks, sometimes vertical lines of them. Not the normal large block digital drop-out thing, just very fine all over ... as if some sort of light noise had been added.

His original footage is clean.

I suppose he's tried the usual dump preferences, restart, reset render preferences? Sounds like a software corruption. Also, what happens if he tries to directly export the FX into QuickTime movies? It would be good to nail down whether the "green snow" (eat that, Frank Zappa) is a problem with previewing or something permanently wrong, such as with FX plug-ins.

I can also offer a similar problem: I was superimposing two heavily effected clips using opacity settings and somehow a "flash" appeared on one of them. Neither clip had a white flash, but after rendering, somehow those two clips always gave me one. Luckily it was an opening credit sequence and I was able to radically change my edit to get rid of it, but the source of the problem remained unknown. "Demon clips", I call them -- sometimes two clips just don't like each other and cause bugs.

I did tell him to dump his preferences and see if that helped - I'm guessing it might, but I just thought maybe someone had seem something similar before.

The snowy clips have no fx - just a sequence exported as quicktimes as far as I know.

Lime Green anything is a little magic in digital video. That's what happens when all three video signals go to zero. You would think that would give you black, but it doesn't. Well behaved picture black is the luminance signal going to "zero", but the color channels all settle down to 128. The definition of bright green is when the two color signals go to zero, too.

If the digital signal goes totally in the toilet, the picture just mutes, usually to black, but when *most* of the picture is still OK and the actual video data is badly damaged, you get lime green. If you interrupt a DigiBeta machine at exactly the wrong time, or it has a slightly damaged tape, the output video goes so green that you can land small airplanes by the light.

Koz

Thinking about this a little more, you may have one of the two video heads damaged. That would give you one flickering picture (television field one) and green garbage overlayed (where field two used to be).

Have yoiu tried the tape on a different machine? It could have been recorded on a damaged recorder.

Koz

You may also want to check and make sure that none
of the footage files have an alpha channel and if they do make sure it is set to none.
I had a somewhat similar problem (Not green tho) and that was my sollution.

Good luck

<<Lime Green anything is a little magic in digital video. That's what happens when all three video signals go to zero. You would think that would give you black, but it doesn't. Well behaved picture black is the luminance signal going to "zero", but the color channels all settle down to 128. The definition of bright green is when the two color signals go to zero, too.>>

Excellent information. So that's why I always see the green squares when MPEG-2 transcoding, etc., goes bad.



- Justin Barham -

Yep - it's definitly the lime green thing - I've seen that a few times before on damaged signals. This is much finer, but it is still the lime version, so great info, thanks Koz. I don't think it's the heads, though, because from memory he said his captured source clips were clean and undamaged.

Thanks for the alpha info too Johan - I won't see this guy for several weeks, but I'll try and remember to post the solution when and if I get one.

I called it lime green because I couldn't spell shartroos.

Koz

you may have cracked this, but going off on another tangent...

the render setting comment was intersting,
it could have been the cause oif some of the blockyness

nick

<<<but going off on another tangent...>>.

...because you can't spell shartuce either?

Koz

Chartreuse

adj : having the yellowish green color of Chartreuse liqueur n 1: aromatic green or yellow liqueur flavored with orange peel and hyssop and peppermint; made at monastery near Grenoble, France [syn: Chartreuse] 2: a shade of green tinged with yellow

No more excuses

:-)



Michael Horton
-------------------