interlace artifacts in 24pN

Z

Zot

Member
So, I've searched this topic and have put myself at ease to some degree, but would just like it cleared up for me. I'm testing 24pN with Thin V detail Frequency and am seeing quite a bit of interlace artifacts. I know that I should be shooting at thick for video out, but just want to be sure that this is normal. Anyways, why do interlace artifacts show up from using a high rez mode?

Also, the reason I was testing this in the first place is because I'll be shooting 24pA for a film out, and thought 24pN with the same scene file settings would give me a better idea what the final product would look like. Unfortunately I wound up with a stair-steppy thing instead. If I am shooting in a thin setting for film out and would like to make video dailies, is there a quick fix for this in FCP4 or other NLEs? Thanks much, and excuse me if this has been addressed before.
 
Re: interlace artifacts in 24pN

the one and only way you get interlace artifacts, is from having an interlaced frame.. of course every 5th frame in the 24pa footage is interlaced, and would be removed by doing the 2:3:3:2 pulldown to make it a true 24p file. so if your actually reffering to actual interlace artifacts, you need to pulldown the footage to make it a true 24p file.

the other possible causes of jaggy edges would be :

1. the codec your using may not use any smoothing, or interpolation , and pretty much is poop
2. the thin mode is causing some "jaggies" due to compression, and subject matter
3. your looking at your nle monitor window when the window is running inb an rt mode, which often causes vertical banding in the image, which is not actually present in the end result, and is only seen in the monitor window due to it running in the realtime mode
4. some other weird thingy

you can always add a slight blur, or use some chroma smoothing or interpolation codec on export to smooth the image if your just getting stair stepped edges, and not actual interlace artifacts
 
Re: interlace artifacts in 24pN

Make sure you not confusing twitter and interlace artifacts. An interlace artifact would be movement between fields and cuasing a "jitter" when parked on a full frame display.

Twitter is cuased by high frequency detail that cannot be resolved with 1 line of video. In this case, you see just the pulsing of the detail area trying to resolve that one line even though the frame is progressive. This is the reason you do not want to make 1 pixel width lines in graphics intended for NTSC broadcast. You want at least 3 to elinminate the problem all together.

The THICK mode does not allow detail to be less than 1 line so it eliminates the issue, but you are not getting the full vertica resolution of the image. You can always apply a VERY small amount of gausian blur or "median" filter type to the problem area of the frame to eliminate the twitter you see in the progressive frame.

Michael
 
Re: interlace artifacts in 24pN

I had the same problem when testing this camera. I wish I had an answer for you. I've looked all over these posts trying to find a solution. It's the one flaw that's steering me away from buying this camera. Plus I think this is just the nature of the format too. Some cameras handle it better than others. However, as a shooter of film, that stepping problem won't go away. It may get smoothed out in the transfer but will still be in the images. If you are seriouse about a tape to film, I would suggest using AJ SDX900. Many more options plus that stepping won't be as much of an issue. Rental prices have dropped a little since it came out. But if Budgetary contraints are the problem and you have to shoot with this camera, ASC has an article on the whole DVX to film thing which might be helpful.

Steve
 
Re: interlace artifacts in 24pN

..steve. its not a real issue, and definitely not a flaw (that the cam can resolves such sharp images). i wouldnt let it stop you from getting the cam if your on the fence about it. most people shoot with a detail level of -3 or lower which pretty much eliminates this issue even when using thin mode. makes beautiful film outs.
 
Re: interlace artifacts in 24pN

As Michael P pointed out, there is basically no reason why you should be shooting Thin mode in 24PN. Thin mode is ONLY for film-outs, and when viewed on a NTSC monitor, it will always create artifacts because of the frequency detail issues Michael P described.

If you're planning a film out, shoot 24PA in Thin. If you're going to video only, use 24PN Thick. If you want an idea of what the film out will look like, just shoot your test in 24PN thick with the detail turned down to -8 or -9. It's a much better indicator than shooting 24PN in Thin, which will give you nothing more than an unwatchable image.
 
Re: interlace artifacts in 24pN

..well using thin mode really isnt that bad. with the detail at
-3 or less(mines at -4) its actually fine, and quite useable for an ntsc out or a film out. ive never really had any issues with using this particualr setting. for either purpose. i also have to take into account the fact that im using a matrox codec which allows me to do chroma interpolation and smoothing on a selectable basis when rendering, but really the footage is perfectly useable even before this. but i guess it all depends on what and how your shooting.
 
Re: interlace artifacts in 24pN

Thanks everybody. I went back and looked at this same footage again on a somewhat more legitimate monitor and could NOT reproduce the same thing I was getting. The picture looked rock solid on my Sony 14mu with the 16x9 mode enabled. However, the original noise was not twitter or the typical rough "jaggies" caused by DV on bright edges. It looked like what an interlaced image looks like in photoshop, but of course it was moving. Sorry if I'm not explaining this correctly. I'm kind of wierded out by it, but since testing it on a more professional monitor, I figure it has something to do with resolution. Perhaps it simply was the Frequency Detail. I'll try to see if I can get the same results with thick mode. If somebody could point me to the ASC article about DVX100 to film out I would appreciate it, I don't think I've seen this. Otherwise I have to say this camera is pretty damn hot. I turned the lights and the sound off on my test footage and I swear I was watching a 16mm reel(this is after some finessing of the Scene File). Except without the light leaks, scratches and hairs, and noisy projector.
 
Re: interlace artifacts in 24pN

Zot... if you give me a day, I can dig that ASC article out and tell you what issue it appeared in. It's a great article.

Steve
 
Re: interlace artifacts in 24pN

Barry.. ya beat me to it. But in case other people are looking, the DVX article is in the April 2003 issue. Best of luck.

Steve
 
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