I am concerned about picture 'judder' and 'flicker' in some of my videos when viewed on TV, and will try to explain what I am seeing against what I would like to see.
My absolute goal is to safeguard my video work against the varying possibilities of TV types owned by clients
There are 2 main issues:-
1] Picture juddering while camera panning - specifically noticable when panning at 'mid-speed' around a background [indoor or outdoor] with no moving 'subject'
2] Bright areas of picture flicker varyingly on TV screens
Here is some further information about my equipment, techniques and research I have done on the juddery panning issue:-
Camera: Canon XM2/GL2 SD PAL [25fps] Editor: Avid Liquid 7.2 Editing codec: 'DV[AVI] 25mbit 4:2:0 PAL'
Pans are executed smoothly on location, miniDV footage ingested via FireWire, editing completed, exported to MPEG-2 DVD 720x576 25fps
Now from what I have found out, the juddery panning issue on TV playback is commonplace with consumer/prosumer camcorders - a reason being differences in screen refresh rates [hz].
So perhaps this explains why video playback of my 25fps panned material on my 50hz CRT TV is just fine, but on my 60hz computer monitor it judders a bit, and on another test CRT TV which has '100hz capabilities' it is even worse.
However I would appreciate some clarity on frame rate against TV hz, and how they may clash. I know very little about refresh rates/hz, and am more confused when seeing for example on the back of my monitor: 100-240V - 50-60hz - 1.5a max. Hz in this context is related to electrical power, screen refresh rate or both?
Is it the case that whenever my 25fps PAL material is played on a TV/display with greater than 50hz, the pans are going to judder? This is alarming, given that most TVs produced now are above 50hz. Is there no 'auto-detect' on new TVs so they play 25fps video at the correct 50hz?
After seeing how my mid-paced pans turn out on some TVs, I am at the moment almost eliminating mid-paced pans from my work in disgust - allowing only very slow or 'active' pans [i.e. with a moving subject, where any background judder is not noticeable].
On my second issue of 'flickering' on TV playback, this happens even in static shots, and is usually centred around white or brighter areas of the TV screen.
I understand a little about 'legal limits' of white and colours, and try to keep the white RBG values under 235. But still I find my films somtimes have that extra unwanted 'video' look caused by parts of the screen flickering [this is not extreme flickering likely to be very noticeable to joe public, but it is happening nontheless].
When I watch a TV programme, the picture can seem to have as much ultra-bright areas as it likes with no evidence of any flicker. I appreciate TV is shot on film or expensive HD-cameras etc etc, but is that really what it takes to be flicker-free, or am I missing something?
I try reducing my Gamma values in editing to keep those bright areas under control [windows in background etc], but can't go to far as I lose detail in people's faces in the same frame. Also I don't want to turn my whites more grey, I would just like them less 'on the surface' of the TV screen.
By this I mean, it's as if pro TV productions are behind an extra 'screen/filter' where they can be as bright as they like with no danger of flicker. How do I achieve this? What about colour Diffusion filters?
Thank you for any help and advice.
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First some definition issues
"Judder" usually means a fast-slow-fast action during a pan. This is usually caused by NTSC telecine (3:2:3:2).
24 fps film and 25 fps progressive PAL has more constant velocity jerks unless the pan is microprocessor controlled to specific rates.
Interlace 60i or 50i show half the jerk.
Do you see this when the Canon XM2/GL2 is connected directly to a CRT TV?
Does this differ from broadcast video on the same TV?
If so it may be a shutter speed issue. Try the default.
Use a shallow depth of field during those medium speed pans (so the background is blurry) if you can. That will help a bit.
I suspect you are deinterlacing your 25i (camera manufacturers call this 50i now, marketing) and making 25 fps progressive DVDs. Leave the video at 25i and it will playback more smoothly. At 50 Hz, 100 Hz, and 200 Hz (without temporal motion vector frame interpolation) the video should be equally smooth. 60, 120, and 240 will have some judder because of the mismatched frame rates.
The 'juddering' I describe = as the camera pans around a room, the movement is not smooth and fluid through DVD on 60/100hz TV [and on my computer monitor during editing -all fine on my old 50hz CRT]. Instead, it's as if the frames-per-second has been reduced [i.e. in the picture at one point in time we see one area of the room, in the next fraction of a second it has 'moved on' too much].
I always leave my shutter speed at 1/50, which is correct for general PAL shooting @ 25fps. Only when I want a specific effect will I change up or down. I'll experiment with pans at different shutter speeds I suppose?
Blurring out the background kind of defeats the object in this case, since the aim of the 'panning segment' is to show off the design of a room interior or the landscape of an exterior location. Hence, the pan ideally needs to be 'mid-speed', rather than very slow [reproduced better on TV but tiresome to watch] or faster [not enough time to see what we're supposed to be looking at].
I can't remember where I read it but someone noted that one of the reasons such mid-paced pans might not work smoothly is the heavy amount of constantly changing pixel information that must be updated every fraction of a second as a camera pans an unpopulated/uneventful room or landscape. Something about every pixel being different during the course of such a pan [with no central 'subject' to concentrate on] meaning that the reproduction on some TVs is strained and will inevitably appear 'juddery/jerky' as the workings of the pan are 'fully exposed'.
As far as I know I am not deinterlacing during my process of converting miniDV footage to DVD. In Avid Liquid this option during timeline editing and DVD conversion remains on 'Interlacing: top field first' and not progressive. I guess I could experiment with 'bottom field first' and also 'progressive' to compare and eliminate.
I'll try plugging the camera directly into the TV and see how pans and flicker look without any video conversion/compression.
I suggest you post 1 second of your source directly from the camera, and the same second after conversion to DVD MPEG2.
Note that shutter speed does not directly determine frame rate. 1/50 second could still be producing 25 fps progressive frames.
The panning would degenerate into macroblock artifacts if you weren't using sufficient bitrate, not jerky movement. Although, I guess it's possible an HDTV's deinterlacing might get confused with severe macroblocking.
Originally Posted by Xenon77
Check that first.
Originally Posted by edDV
Yes, MiniDV is BFF and flagging that backwards on DVD would result in fast jerky motion -- 25 back and forth jerks every second.