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Thread: Trying to reduce judder & flickering

  1. #1

    Default Trying to reduce judder & flickering

    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 that 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.

  2. #2


    Rather than over thinking this too much there is one thing to keep in mind.
    The DV.avi files you are dealing with are lower field first. The key to dealing with these is to maintain, as much as possible, those properties you can through to the DVD production point.
    So in your case make sure that when you have finished editing and are producing the DVD compliant MPEG2 files for DVD burning, make sure the field order is maintained at lower field first and the frame rate 25fps is kept and the resolution of 720x576 is the same.

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