Sawtoothing on DVD

Is there a way to minimize the "sawtoothing" I see on my SD DVDs? My project is shot 1080i, AVCHD in a ProResHQ timeline. Fullres output, then into compressor using the default 90 min SD DVD setting...burned with DVDPro. Looks great out of the edit system (FCP 7) and when the DVD is played on a large monitor, but the "sawtooth" edges really show up on flat screen TVs.

Thanks!

i have no hands-on experience with this, but...

i have seen advice that recommends a first pass though compressor to reduce the frame size.
actually the advice i saw was recommending After Effects.
better scaling, or maybe just faster than Compressor's "Best" setting.

THEN you make the DVD.
i seem to recall i asked about tweaking the Compressor DVD setting to give it better re-scaling,
and the reply was that would be a longer process (downscaling and converting to mpeg at the same time).

just passing on what i read.
hope it helps


nick

This tutorial works well for HDV combing. Never tried it with AVCHD.

[www.kenstone.net]

Quote
preditor
Looks great ... when the DVD is played on a large monitor, but the "sawtooth" edges really show up on flat screen TVs.

Why this difference? The first play uses a software player, perhaps Apple DVD player, together with the computer's graphics card. The second play uses an altogether different player and graphics brain. How much sawtoothing is really in the mpeg-2? The first player could be smoothing it. The second player could be exaggerating it.

The .VOB file can be played with MPEG Streamclip, with the window set to 100%, and closely examined. How's the sawtoothing?

Sawtoothing occurs along slanting sharp edges. Obviously a pixilated image must have some of this. This as been called "aliasing", but it is different from aliasing proper wherein pseudo-resolution artifacts arise from planting too fine (sharp) an image onto too coarse a pixel grid. In this case the coarse pixels themselves are sharply visible, with their own detail involving much higher spatial frequencies than the pixel-by-pixel sampling justifies. Different monitors and projectors do produce unequally sharp pixels, but different players (in the broad sense) can provide some immunity by judicious softening of slanted sharp edges.

To make a DVD which will not sawtooth with the worst player using the worst display you must instill that judicious softening in the mpeg-2 yourself. I'm inexperienced with this, and others might have better suggestions, but I think you should first make an SD ProRes in Compressor, then filter that in FCP, then export a ProRes, and from this make the mpeg-2 in Compressor. For the FCP filtering I'd suggest a pair of Directional Blur filters, one at 45 deg and one at 135 deg, each with 1 unit of blur.

This filtering should be distinguished from straightforward anti-alias filtering applied to an HD original before it is reduced to SD. For this I've found {0.3 Gaussian Blur + 1 Anti-alias} good for progressive DVDs and {0.5 Gaussian Blur + 1 Anti-alias + 0.7 Directional Blur at 90 deg} good for interlaced DVDs.

Dennis Couzin
Berlin, Germany

Pretty much what DCouzin said about aliasing- what kind? Also bear in mind that a bad camera has higher noise levels, which is bad for image processing. Also, Avchd has 4:2:0 chroma sub sampling which makes blocky chroma pixels, and that isn't great for down conversion or image manipulation.

However, I disagree that using blur filters in FCP will produce a superior image, as it is a little like trying to hit a nail with a sledgehammer. There are much more sophisticated algorithms and processes out there. But for starters, I would use Compressor and down convert at best quality. It's pretty good but takes loads of time.



www.strypesinpost.com

For those who need decent and quicker results, I find going from a native HD ProRes SQ export directly to iDVD (part of Apple's iLife packages up till a year or so ago) yields a great widescreen playable DVD without much aliasing or any fal-de-ral. Perfect for low budget clients who can't afford having you drill into DVD SP authoring.

I believe Apple still offers iDVD on the App Store for fifty bucks or less. They have discontinued it on new machines in their effort to social-engineer media use, a habit which should be discontinued itself.

Not everybody wants file-based product. Disc delivery will be around for another decade, and it's a pretty good 25-year archival format, but in the here and now, most all my clients want review discs with timecode or final cuts for event projection. HD looks pretty code transcoded to MPEG-2 with no hassle for review and approval, and BluRay looks stunning for final delivery projection.

I guess the alternative is Roxio Toast.

- Loren

Today's FCP 7 keytip:
Advance to next/previous keyframes in a clip with Shift/Option-K !

Your Final Cut Studio KeyGuide™ Power Pack
with FCP7 KeyGuide --
now available at KeyGuide Central.
www.neotrondesign.com

Quote
strypes
...a little like trying to hit a nail with a sledgehammer.

Yes, the sledgehammer is the FCP blur filter that inflicts itself on every pixel of the image. A "judicious softening of slanted sharp edges" (my words) could be an algorithm that identifies exactly the sawtoothing and neatly airbrushes it out.

In preditor's example the sawtoothing seems less due to the downscaled mpeg-2 than due to the upscaling done by his TV screen DVD player. So a smart algorithm used before the mpeg-2 must anticipate where a later upscaler could exaggerate sawtoothing; the algorithm must substitute a less vulnerable edge structure there. This must result in a softer than ideal edge (when the DVD player is not one that does poor scaling).

We're dealing here with a problem of downscaling followed by upscaling. Blur filters, and more specialized anti-alias filters that still inflict themselves on every pixel of the image, have useful roles in downscaling. The task of making a downscaled image that is immune to bad upscaling is a separate task. I think the immunizing smart algorithm is best applied to the already downscaled, but not yet mpeg-2 compressed, video. A case can perhaps be made that sledgehammering, sacrificing sharpness globally, will look more natural.

Dennis Couzin
Berlin, Germany

preditor wrote "My project is shot 1080i, AVCHD in a ProResHQ timeline."

I think downscaling an interlaced video will always cause problems with the standard means of FCP.
dcouzin had a good method for de-interlacing to 50/60 fps in another thread.
Though it takes probably a lot of time it might be an idea to convert the "i" sequence to a "p" sequence with 50/60, then downscale and re-interlace again.

-Andreas

Some workflow tools for FCP [www.spherico.com]
TitleExchange -- juggle titles within FCS, FCPX and many other apps.
[www.spherico.com]

I have the solution, but you may not like it.

We encounter this on virtually every mpeg based project including any flavor of XDCAM.

There are several options.

1 - transcode everything to pro-res before editing...and edit a pro-res timeline

2 - keep your native XDCAM format (or other mpeg based) and have your timeline render everything in Pro-Res

3 - and this is what works for us but it's time consuming and creates enormous files - export from your timeline to ANIMATION codec.....then take that into DVD Studio Pro - that virtually eliminates the sawtoothing.

We have non of this problem with DVCPRO-HD - only various versions of HDV (yes XDCAM is just hdv on steroids)

There will be graphics that may be a problem with fine lines that you may need to blur a bit in photoshop

There may be scenes with high contrast and fast camera movment that won't compress well - I suggest adding compression markers -- or try deinterlacing just that scene before rendering out


All of this works for us after long trial and error

Thank you for your help...choosing "None" in the dominance window did reduce it a bit. I shoot a lot in 720p, which seems to be better than this project in 1080i.