Interline Twitter and sharpness

[Lou Bruno]

Check this out:

Progressive scan - Wikipedia, the free encyclopedia


This is what I am observing with the XF-300 before lowering the sharpening to -7 and adjusting coring to +12.

[Bill Weaver]

So Lou, are you saying that these settings have dealt with shimmering issues? Downconversion to 720 OK?

[Antony Michael Wilson]

Lou's settings should give you an alias-free starting point at 1080, which is essential but that still doesn't guarantee good, clean 720p or SD. You need an alias-free starting point AND a good scaling algorithm to deal satisfactorily with pictures that start off this sharp. The scaling process itself can and often does introduce substantial aliasing. I'd say, try Lou's settings then do your scaling and Apple TV encoding in two separate steps: Try the 720p down-convert in something with good scaling like After Effects, rendering to a high quality codec (or ideally uncompressed) then, if the results are good, encode the 720p high quality down-convert to H.264/mp4 at the same raster. By breaking it down into steps, you should start to see when and what is introducing aliasing. Obviously, you need to start with alias-free images!

[Lou Bruno]

Antony is 100% correct. I am even thinking of totally shutting off the sharpening and adjusting in post.

[Bill Weaver]

These perspectives help a lot.

I love hearing more software suggestions, post techniques that optimise the quality of the XF....

Anybody else?

[Alister Chapman]

You might want to take a look at these:

XDCAM-USER.COM Getting good SD from an HD camera.

XDCAM-USER.COM Getting SD from HD and the problems of oversampling.

Hope they help.

[Jeff Anselmo]

Thanks for those links Alister!

I've had to put in a 2sec shot (shot with the XFcam at 24p) in an SD timeline, with 30p footage shot with the Canon XL2. I ouputted a WMV file rough cut to show the client, and even with the 2 second shot, the aliasing and twitter-effect is apparent (to my eyes at least!).

Will try to put a filter on that clip and see how it looks :)

Best,

[Tim Bakland]

I've had good results by:

1. Exporting the XF300/100 footage as Quicktime Movie

2. Pulling that into compressor and using Frame Controls to improve down-conversion.

It's the best method I've found so far when needing to go to SD or pair with SD or deliver on DVD.

[Bill Weaver]

I've applied the method for taking HDV down to SD via this method, and gotten some beautiful images:

Exporting HDV Video from the Timeline to Standard Definition DVD

[Antony Michael Wilson]

Originally Posted by Jeff Anselmo

Thanks for those links Alister!

I've had to put in a 2sec shot (shot with the XFcam at 24p) in an SD timeline, with 30p footage shot with the Canon XL2. I ouputted a WMV file rough cut to show the client, and even with the 2 second shot, the aliasing and twitter-effect is apparent (to my eyes at least!).

Will try to put a filter on that clip and see how it looks :)

Best,

Simply placing HD images on a SD timeline in FCP will definitely introduce scaling artefacts because FCP's internal scaling is very, very poor. I know many people do it and think it's fine but it will only produce acceptable results if your standards are low or the source footage isn't actually very sharp! High quality video scaling is difficult to achieve well and needs a sophisticated algorithm. Adding a blur may help in some circumstances but it is no substitute for using the proper tools. Compressor does a much better job when you enable the frame controls and choose best quality and fine tune the edge enhancement to your footage but it is extremely slow.

[Doug Jensen]

Quote: "Simply placing HD images on a SD timeline in FCP will definitely introduce scaling artefacts because FCP's internal scaling is very, very poor."

I completely disagree with that statement.
If you have the right workflow, you can get beautiful results with HD clips on an SD timeline. I've been doing it for several years and my standards are not low. I think most people who have viewed any of my camcorder training DVDs would agree that the results look very good. All of those were edited on an SD timeline. Getting nice results is not hard, and it does not require any additional FCP plugins, no 3rd party software, and no need to add blur. That is a myth.

The advantages of shooting in HD, even if you will be editing on an SD timeline are:
1) You'll have your raw footage archived as HD for future use.
2) You can scan, pan, and zoom within the HD frame to change your composition. Same thing you can do with stills.

[Antony Michael Wilson]

I respectfully disagree with you, Doug. We've been in the post business for many years and FCP's scaling is extremely weak when compared with hardware from Snell and Teranex, for example. Generally, NLE software scaling is weak and not adequate for broadcast SD deliverables from HD sources. This holds true for Avid and FCP. Avid hardware is better but problematic with excessive sharpening by default. Kona hardware is the way to go on FCP if you're on a budget. It does a decent job on most HD down/cross-converts.

Doug, I have one of your training DVDs and it is simply excellent, thorough and well presented - a superb training resource. However, there is plenty of high frequency aliasing from the XF-derived footage even viewing it on a SD CRT grade1.

Bottom line: High quality scaling involves complex computation and most of the popular NLEs do not do a very impressive job. High-end hardware is the fast simple solution but if you're on a budget, edit at the format's native raster and experiment with software down-convert solutions until you are happy with the quality you get. Of course, you also need to make sure that you are starting with alias-free images and - in the case of the XF - this means reducing in-camera sharpening.

[Mikko Topponen]

FCP scaling is only bad when you mix up your interlace settings. Trying to scale material that FCP deems as "interlaced" will look horrible. Scaling material that is properly set as progressive will do pretty well. I've seen lots of professionals do bad jobs with sequence settings and then I've had to fix them one clip at a time. FCP does not repair sequences with the wrong settings even if you switch them correctly after doing them wrong.

Saying there's aliasing on an SD-interlaced CRT monitor is like saying the sky is blue. Yes there is aliasing, there will always be aliasing with interlaced signals and monitors.

[Antony Michael Wilson]

Deleted - double post.

[Antony Michael Wilson]

I quite agree that an elementary understanding of video technology and the software itself is a good starting point for any such task. Nevertheless, even using FCP at its best, scaling is relatively weak. If you're happy with the results using FCP software scaling for down-conversion, that's great but for those who are not happy, it's a good idea to break the process of creating SD deliverables down into steps and one of the steps that may or may not be causing additional aliasing issues is FCP (or Avid for that matter). Of course, SD is - by definition - interlaced, no matter how the source itself was scanned and a CRT grade 1 is the best tool for critical picture evaluation. It is usually possible to control aliasing in SD to an acceptable level - even from super sharp higher res source material - with a bit of effort and the correct tools for the given issue/picture. The level of aliasing to which I am referring is excessive and avoidable.

It is crystal clear from our tests that good quality alias-free SD images (viewed on a CRT/computer screen/LCD/Plasma) are almost always possible from XF 1080p sources with the right combination of camera settings and post processing techniques and equipment.