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Does the nano help reduce interline twitter on EX-1

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William Urschel
Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 12:46:09 pm

I have an EX-1 and am seriously considering purchasing the Convergent Designs nano Flash - My primary question is - does using this device for continual I-frames REALLY help much with detail in fairly quick pans shot at 1/120th second 1920 x1080 30p ??? Or maybe it doesn't help at all - personally, I don't care about the improved colorspace from this device instead of using the stand alone typical camera recording.

I understand that use of the nano notably reduces some artifacts (which, of course, is not at all suprising), but the major problem I would like to overcome is INTERLINE TWITTER, for which I currently have two work arounds, but both of which reduce resolution of the superb capture of this camera! I am talking about interline twitter when the shot includes either some VERY fine horizontal lines or very sharp horizontal edges/high contrast. I'm using the Adobe CS4 products for editing and BD production - my Sony HDV cameras (four of those!) produce great BD and DVDs - but when I go to the far better resolution of the EX-1, I run into the problem of the twitter.

I AM interested in the opinion of anyone who has actual experience with this device on any of the EX 1, 1R, or 3 products as to whether there are ANY advantages otherwise beside the improved colorspace.

I am sitting here already with $5,000 worth of SxS cards (purchased at that full price 1 1/2 years ago), and am not interested in spending another small fortune in a device, its cards, and the MainConcept program for use in Adobe Premeire CS-4, unless there are some really substantive advantages!

Anyone with actual experience - your reply would be much appreciated!


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Bill Ravens
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 12:54:10 pm

I think you'll find the twitter problem is all but eliminated at bit rates of 100mbps or higher. As an aside, are you using much sharpening in your camera setup? Sharpening, in-camera, exacerbates the twitter problem.



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William Urschel
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 1:53:29 pm

Thanks, Bill (Ravens)! Am NOT using in camera sharpening - spent 1,700 hours (!) last year, after hours, according to my time reports, doing everything I could think of to get rid of BD exhibited interline twitter and abomination of down rezzed DVDs. Finally gave up on DVDs entirely, except the beauties produced in downrezzing those resulting from HD on all my Sony HDV cameras!

Amoung my "experiements", under very carefully controlled and documented conditions: 1)tried 5 different settings in PP for "detail" on the camera - finally removed twitter, but the pictures were so badly smeared that one of my old, 1991 Sony cameras
produced far, far better pictures (in SD, of course). And I purchased Vegas Pro (to try out versus Adobe Production Permium CS-3 and CS-4), and SEVEN other apps (darn, some were quite expensive!) for downrezzing from HD to SD and encoding for BD and DVD, all to NO avail. I have been using Cineform (last, Prospect 4k) for years, and to GREAT advantage in handling HDV editing enhancement and backup. But, absolutely surprising to me, going to Premier, Adobe Encoder, and Encore in CS-4, without Cineform, produced the least artifacting and interline twitter.

And by the way, I have had other editors check out my work flow, etc. to no avail.

I have come so close to getting rid of the EX-1, until I went to CS-4 without Cineform (Cineform wil not work with appropriate functionality on Premier Pro CS-4, though it will probably come back with CS-5!)- I'm still getting some interline twitter, but nothing like what I had before, and I am now partly satisfied with the results.

In any event, Bill, your comment about going to 100k with nano as a method of avoiding interline twitter - QUESTION - is this opinion based upon your or one of your compatriot's actual experience? If so, then I don't care what it costs, I'll go for it, to end over a year of total grief and frustration for this otherwise absolutely superb camera!

Thanking you or any others for your informed response, I remain your humble servant,

Bill Urshel


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Rafael Amador
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 1:14:32 pm

Hi Willians,
How the NANO improve the pictures on pans you can see it at 50Mbps.
About the INTERLINE TWITTER, that's not a matter of the NANO.
The NANO just record what the camera outs; If the INTERLINE TWITTER is the SDI you won't get rid of it even if recording fully uncompress.
Adjust the camera.

[William Urschel] "I am sitting here already with $5,000 worth of SxS cards (purchased at that full price 1 1/2 years ago"
This is why last year, instead of buying more SxS cards, I bought the NANO.
For 5k you can buy the NANO and 2.000 $ worth of CF cards; that means some 32 hours EX recording (when buying top quality CF cards).
Sell the cards and buy the NANO; even if you don't care of the better color space.
Best,
Rafael



http://www.nagavideo.com


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William Urschel
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 1:56:51 pm

Rafael

Thank you - good point re selling! Probably get less than $400 a card (very poor return on investment!), but every little bit helps, doesn't it!

Thanks again.

Bill Urschel


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Michael Slowe
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 3:19:06 pm

Having also been driven mad by line twitter on SD DVD's (don't see it on tape) i found that the new versions of the MPEG 2 encoder BitVice virtually solved the problem. It's a great encoder and Innobits (the Swedish company who make BitVice) are continually developing and improving their product. The problem is of course that the EX cameras are giving us too sharp an image!

Michael Slowe


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Tim Kolb
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 4:53:16 pm

Hmmm... several issues here.

"Interline twitter"...I'll assume we're referring to what engineers would refer to 'aliasing' or 'mosaic' which would occur on clothing with a fine herring bone pattern where it looks as if the cloth is crawling off the person...and is most common in interlace signals.

If you are shooting 30p, I'm not certain how you would produce this artifact...at least to the extent you would see it in interlaced mode. The monitor you use to view your video has an impact on what you see vs what you actually have...not to mention that on many NLEs, the viewing window (panel, canvas, whatever) will usually scale the actual pixel size to fit within the interface and this will also produce some interesting artifacts that aren't actually in the file.

Your HDV gear (if it's Sony) is likely dropping to one field if you are choosing progressive mode, effectively halving the vertical resolution (to 540 vs 1080), softening high frequency artifacts far more than an EX1 would, which is shooting full resolution vertically (1080), not to mention 33% more resolution horizontally (1440 vs 1920).

As far as panning goes...with progressive scan, you will never have the same smooth motion as you would with interlace. This is the reason why cinematographers have very specific speeds that they know they can pan with any given lense...they have to adjust their technique to reduce "judder".

100 Mbit I frame vs 35 Mbit Long GOP... I'm an advocate for the Convergent Design product line as much as anyone. There is no question that the Flash XDR and the Flash Nano are really well thought-out devices and that 100 Mbit I frame is very good quality.

However...there are a few caveats here.

1. Temporal compression is typically AT LEAST 2.5 times as efficient as I-frame only codecs, all other compression traits being equal. This being the case, 100 Mbit I-frame MPEG would carry about the same image quality as 40 Mbit long GOP. Again, this is assuming all else is equal. So going to 100 Mbit I-frame likely won't grab the advantage over 35 Mbit Long GOP that one would assume by judging on the raw numbers... (100 Mbit Long GOP 4:2:2 is an obvious jump however).

2. However...XD(EX)cam is 35 Mbit 4:2:0 whereas the Nano records 4:2:2 at data rates above 35 Mbits, so you have denser color difference subsampling. Advantage for quality goes to the Nano on this point...

3. BUT...whether this would resolve the fine pattern noise issue is in question in my mind. The camera's low pass filter system combined with it's detail circuitry is where the rubber hits the road here...and the Nano and the camera have equal recorded luma resolution...1920x1080. I don't think the fine pattern noise will be affected by the recording system in this case quite frankly.


I'd say the Nano is a very sound investment...but I think that the nature of the visual issues you are referring to lead me to believe that there is more to this story and that without some other alteration in how you are using the camera or you are viewing the footage, I'd be surprised if switching to the Nano -alone- would solve the problem.

...I will say that my conclusions are based on what I believe you are describing. If I'm misinterpreting your comments, feel free to clarify.




TimK,
Director, Consultant
Kolb Productions,


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Bill Ravens
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 9:06:40 pm

I agree with you Tim. Your post made me think of another factor. Downrezzing HD(1920x1080) to SD(720x480) is inherently a problem, quite different from the twitter that results from bandwidth limiting and compression artifacts. In my experience, if one is aware of the need for downrezzing in their workflow and delivery, 1280x720 makes a much prettier source for downrezzing. Having said this, there are several techniques posted on the internet for mitigating line twitter when converting HD to SD.



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Don Greening
Re: Does the nano help reduce interline twitter on EX-1
on Feb 8, 2010 at 11:18:45 pm

Great post, TIm. It's worth a light bulb.

- Don


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Rafael Amador
Re: Does the nano help reduce interline twitter on EX-1
on Feb 9, 2010 at 2:46:00 am

[Tim Kolb] " which would occur on clothing with a fine herring bone pattern where it looks as if the cloth is crawling off the person."
Tim,
Where there is a lot of B&W detail, the frequency of the Y channel some time gets close to the frequency of the Color Subcarrier. The filters read that Luma as Chroma,producing these ever changing colors.
Is not a fault of the camera, but of how the NTSC and PAL system have been designed.
That's call "moire" and there is nothing to do avoid it.
I guess that you can tweak the detail to avoid it, but probably will kill the picture.
Best,
Rafael



http://www.nagavideo.com


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Tim Kolb
Re: Does the nano help reduce interline twitter on EX-1
on Feb 9, 2010 at 3:33:59 am

[Rafael Amador] "Where there is a lot of B&W detail, the frequency of the Y channel some time gets close to the frequency of the Color Subcarrier. The filters read that Luma as Chroma,producing these ever changing colors.
Is not a fault of the camera, but of how the NTSC and PAL system have been designed.
That's call "moire" and there is nothing to do avoid it.
I guess that you can tweak the detail to avoid it, but probably will kill the picture."


Well...aliasing happens in many instances and from many sources and NTSC color isn't the sole cause...subcarrier moire is one...though in HD, there is no analog color subcarrier.

If you have any high frequency detail that is above 50% of the max sensor spatial resolution, aliasing will happen. Nyquist tells us that you need to sample at 2X the max frequency you wish to faithfully reproduce. This is the reason why the low pass filter on any electronic camera should be cutting out detail above 50% of the max sensor resolution, but there are still situations where aliasing can happen.

Turn up the detail on your video cam and find out...







TimK,
Director, Consultant
Kolb Productions,


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Rafael Amador
Re: Does the nano help reduce interline twitter on EX-1
on Feb 9, 2010 at 3:07:52 pm

Very clear technical note, Tim.
Avoiding this kind of fabrics and textures have been a rule of thumb.
Rafael

http://www.nagavideo.com


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Alister Chapman
Re: Does the nano help reduce interline twitter on EX-1
on Feb 11, 2010 at 7:53:53 am

It's well known that turning the detail level setting on an EX1 or EX3 down to -8 or lower reduces in camera aliasing. This also helps with SD down converts. I find I get my best SD downconversions when I reduce the resolution of the HD by roughly half before converting through the use of a mild blur filter or using a line blending filter(field blending) such as the flicker reduce filter in FCP. Again it's all down to Nyquist theory. When down converting to SD you are starting with too many samples unless you soften the image first. For SD you don't want more than 500 lines of resolution.

I have a NanoFlash and I have to use the same blur or softening process to get good SD down converts from HD. If I'm shooting material where SD is important then I will often shoot 720P for a better down converted result.

Alister Chapman
http://www.xdcam-user.com


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William Urschel
Re: Does the nano help reduce interline twitter on EX-1
on Feb 16, 2010 at 5:25:10 pm

Gentlemen: Thank you ALL for your thoughtful responses! I've been away ill, and am now sort of back, after purchasing the Nano last week after my last post.

To Michael Slowe - Thanks, if I had an Apple, I'd purchase the Bitvice then in a millisecond, but several years ago the cult at Apple really messed with me, and I swore off Apple forever (by the way, I'm SO happy with Boxx and Vista Professional 64k and (even!) Adobe PP CS4 I could bust!

To Tim, and thanks to you.....as I've posted elsewhere, I'm an expert home theater builder for myself and others for just short of a quarter of a century, and the blasted twitter shows up on all of my very carefully calibrated equipment, AND every one of my customers, without exception, unless they have a very low resolution piece of junk, and then, of course, other issues appear. Also, with HDV, I've used only interlaced. Also, the 1,700 hours I spent last year trying EVERYTHING included setting the EX1 at at least 5 different detail levels, and on at least two of them, the twitter on fine detail was pretty much taken care of and the pictures were smush.

And to Alister - yes, 720 makes for great SD renditions, but I hate loosing the beautiful detail possible with 1080 (even with the slight detail reduction after rendering out Adobe's anti-flicker. And for shots in 720 involving a lot of momement, my absolute preference would be for 60p, but unfortunately, the BDrs I make (always using Verbatim) - too many of them will not playback reliably on customer's machines, same machines which have no problem with anything else I make!


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