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GH2 in 24p: noticeable "strobe effect" with any motion in frame?
  • 259 Replies sorted by
  • Since you've locked in Aperture and ISO, is it possible that outdoors, the camera is over-riding shutter speed as its only way of getting the exposure right?

    Do the individual outdoor frames look motion-blurred?

    Thanks for the testing.

  • Well, cam was in Manual mode, and I never saw 1/40 shutter change during recording - rather, it stayed the same as it should.

    So if you look at the values as reported by camera's display, shutter should be the same throughout.

  • @mo7ies Erm...: more light - better/sharper image opposite to less light - less sharpe but more blurred/grained picture in the first place for stills. So why shouldn't this also apply to film?! I'm not wondering about your findings - for me this totaly makes sense.

  • Are the outside-shot frames motion-blurred ? [Does anyone know if there is any meta data in GH2 video file(s) which might show the shutter speed?]

  • @roberto: I was surprised if his outdoor shots had no blur at all - if the panning wasn't really, really slow. Whereas the inside shots probably look a bit blurred in the first place due to worse lighting (compared to the outside shot).

  • FWIW, I tried an outside pan today. Plays back without stutter in spite of blocky artefacts during fastest part of pan - which are surprisingly visible only in pause mode. See correct motion-blur at left, artefact grab at right. Note: normally this sort of glitch would mess up the shot and it's unacceptable of course, Maybe VLC fell back to some error-correction mode and managed to play it smoothly anyway.

    smooth.png
    960 x 540 - 188K
    BlockyArtefacts.png
    683 x 384 - 203K
  • Are those artefacts only in a few frames or in all frames when in pause mode? From all I know this is caused by high compressing codecs: not all the information needed for a full frame is available for every frame - thus causing artefacts when displaying one of them (there's only data for the parts where there are changes within the frame while not changing parts of the frame still are there from previous frames). And just out of curiousity: How did you take the screenshot without artefacts (not paused)?

  • Yes, I know it's a compression artefact. It only appears on a few frames. Both screen grabs are paused. I'm quite sure it has nothing to do with the stuttering people are reporting. I originally intended only to show you what each frame of good motion blur looks like. That movement across the frame cannot be achieved by soft-focus alone.

  • Isn't this what LPowell refers to as "farkle" ??... High contrast edges strobing when panned.

    http://personal-view.com/talks/discussion/comment/8788#Comment_8788

  • Just yesterday, completely by accident noticed heavy strobing and judder in a scene in Life of Brian (1979). It’s in the very beginning of the scene in which Brian is brought to Pilate (about 38 minutes into the movie). The camera pans to the right and the columns on the left with alternating, high-contrast ridges on them exhibit something I’d call an extreme version of strobing.

    Here’s the snapshot of the first frame of the scene:

    Life_of_Brian.png
    1280 x 692 - 1M
  • @mo7ies OK, re-formatted fast SD card and installed Sanity 4.1 to match your settings (and eliminate the artefact red-herring problem) Sorry, only see nice, smooth motion-blurring with f8.0, 160 ISO 30 shutter, Nostalgic and 14mm pancake. Nice blurring = smooth playback. @Rambo - I'm not sure what @Lpowell was specifically referring to - but at present @mo7ies seems to have cured stuttering with motion-blur in post. So I'm personally looking for under-blurred frames which would cause stuttering. @Mr_Moore - If that screen-grab is grabbed from the middle of the strobing/judder you mention, I'm not surprised; it should be blurred. I sometimes find it hard to make sure the GH2 shutter stays locked on the "normal" (180 deg) setting. If it were somehow slipping into high shutter speed, that would be a simple reason!

  • Blurring stops stutter. Having worked in animation for 25P PAL broadcast, I automatically look to lack of motion blur when there's a stuttering problem. Whether painting the blur onto a cell, creating a bigger, flatter arm for a gesticulating plasticine [Gumby] or blurring a virtual cell in Amiga's Deluxe Paint, blurring invariably made the motion smooth again. So I automatically look for under-blurring as the culprit with the GH2. What's more, we shot like everybody does, "on two's," creating a new image, then reaching above to click twice on the Bolex's single-image lever. So each 24-frame second really only contained 12 images - which was still easily enough to sustain the illusion of motion!

  • @Roberto

    If that screen-grab is grabbed from the middle of the strobing/judder you mention, I’m not surprised; it should be blurred.

    This is frame #1 out of 168 frames while the columns are in the filed of view. The pan is fairly even, and each frame has approximately the same amount of blur as the one I posted.

    Perhaps I wasn’t clear enough in the post. My point was that strobing and judder are not something unique to the GH2 as some people seem to suggest, but rather the inherent artifacts created by the 180º shutter, 24fps, and faster-than-recommended pan speeds. It’s true that while it’s not always an easy process, one can change the shutter angle in a film camera. I have no information whether it was the case for that particular scene in Life of Brian, but I think it’s a safe bet to say they shot at 24/180.

  • Yes, you can expose shorter than 180 degrees (think Private Ryan), but not longer.

  • @Roberto >> Sorry, only see nice, smooth motion-blurring with f8.0, 160 ISO 30 shutter

    I chickened out and didn't go as slow as 1/30 shutter. I started with the "proper 180 deg" 1/50 shutter, then backed down to 1/40 and that seemed to help smoothing out the motion a bit.

    By the way. By strobing/stuttering I meant not just pans. Anything that moves in the frame, produces the same unpleasant/unwatchable effect with GH2 - apparently more so than with other cams. Think wide outdoor shot of a street, with a person walking at normal speed. Major strobing on that person!

    I gather 1/30 shutter would help even further! I just didn't try it yet. And of course it'd also help with light sensitivity indoors with slow lenses, exposing GH2's sensor to even more light.

    So can we say that two major contributing factors to the exacerbated stuttering on GH2 are:

    1. Scenes with High-contrast edges and
    2. Shutter speed, which on this camera is not slow enough to produce nice blur even at 1/50 (regular 180deg shutter)

    1) may not be avoidable/controllable, but 2) by dropping shutter speed to 1/30 we may re-gain the pleasant motion blur with GH2.

    Is this a current consensus?

  • My theory is that it's due to rolling shutter. At 24p it takes about 25ms to scan the frame, which is the same speed as a 1/40 shutter. Since it scans from the top down, the bottom image gets skewed and then the next frame "jumps" at the top relative to where the bottom of the previous frame was. Subtle, but there.

  • So you're saying 1/40 is the way to go?

  • @yeehaanow

    Since it scans from the top down, the bottom image gets skewed  . . .

    Relative to what you’re viewing on the screen, it’s the other way around—bottom up.

  • Right. I had it backwards. The sensor scans top to bottom but the image is upside down so it starts the scan at the bottom relative to the image you see. @rozroz- 1/40 would seem to make sense. I don't know. Just a theory of mine.
    For this to be true, it would also have to be true for other cameras with similar rolling shutter speeds. ie: 7d, 60d, t2i etc...

  • Thanks for the link, but it is yet another electronic device the size of a 4x4 filter, and:

    according to Tessive.com: "The complete Time Filter system $7,900"

    How appropriate would this be for use on GH2 ?

    The principle seems to work well, though:

    In the meantime, I think Roberto's link/suggestion above to re-introduce some motion blur in post via After Effects seems to be the winner. This way, no motion - no blur, everything is 100% sharp; but with motion, edges will get force-blurred, so hopefully no more stroboscope galore.

  • @mo7ies I meant not just pans. Anything that moves in the frame

    Yes, of course; failure to motion-blur prevents us from using a whole armoury of film making techniques including the one where a bus sweeps across the entire frame, the fun, zip-pan accompanied by that "whoosh" sound -and more. If you shoot everything at 1/30 you'll also end up blurring shots you want to show only slight movement in. 1/40 is considered normal and is what almost all films use. (When Bolex Reflex came out with a variable shutter it was mainly for sport & scientific purposes). You've shown how we can salvage short stuttering sequences in post by painstakingly applying motion-blur. So a worst-case scenario might be that we keep the shutter on 1/40 whenever shooting at 24 fps and live with it. Let's hope we can find a better solution.

  • What's the cons of using a 1/40?

  • @mo7ies 2)Shutter speed, which on this camera is not slow enough to produce nice blur even at 1/50 (regular 180deg shutter)

    Once again, my own 1/40 shots blur movement nicely so I cannot reproduce the problem. But If you post grabs of the offending stuttering frames, I'm willing to bet they're under-blurred.

    Now please everybdy, post just one of these stuttering frames and we can confirm this. If you post two consecutive frames, we can see if the action is close enough for smooth motion or else if somehow a frame has been doubled or missed (another, rare problem).

    The story of the rolling shutter may hold true, but hey, if it's blurred movement, I could squeeze a blurry Bugs Bunny into that moving sequence and you'd you'd never know. [except by osmosis - you wake up longing to chew on a carrot]