"Banding" Issue When Shooting Laser Show Videos

Discussion in 'Lasershow Designer BEYOND' started by base851, Jul 29, 2017.

  1. base851

    base851 Member

    This isn't necessarily a Beyond-specific question, though I am using Beyond Professional to control my projectors.

    I'm in the process of making some demo videos in my studio and having problems eliminating a "banding" phenomenon... I can get nice, clean, sharp video between 24-30 fps, but I'm seeing a pattern of dark bands crossing the screen diagonally at regular intervals. I've tried all kinds of iris, shutter & gain settings to deal with it, but the settings which provide the best quality video also have the problem most noticeably.

    I'm assuming there's some sort of synchronization issue going on between the camera's shutter/iris settings and the frame rate coming out of the projector. I just can't seem to get the two to line up.

    My camera is a Sony PXWZ150, so I know camera quality isn't the issue, just a settings issue. I generally shoot full manual... full auto looks awful.

    For those of you with experience recording video of laser shows... especially if you're using Beyond... can you offer some tips for how to resolve this sort of problem? Is there something I can do on the Beyond side to sync up with the camera, or vice-versa?

    Any suggestions would be appreciated! :)
     
  2. base851

    base851 Member

    I did some experimenting today. I was able to mitigate it fairly significantly by making adjustments to the scanner and animation speeds, but not remove it completely.
     
  3. lorenzopompei

    lorenzopompei Active Member

    I saw the same problem, but not even with professional cameras we got the problem, it slows down by changing the scan rate, but it should be adapted for each animation
     
  4. base851

    base851 Member

    Yeah that's basically what I wound up doing... pick a camera frame rate that I thought attainable by all of my cues and set the scan rate accordingly (by tracking the FPS at the bottom right of the screen) on a cue-by-cue basis. What I found though, was that within a given cue, despite a concrete scan rate, FPS often fluctuated depending upon the load on the projector.

    I was beginning to think it was just me until more looking around found that the "mismatched frame rate" problem is a fairly common (and insanity inducing) thing when taking video of laser shows.

    In fact, now that I sort of have an eye for it, I noticed even the placing ILDA videos had it, though they either matched the rates better or had a good debanding plugin in their video software.
     
  5. base851

    base851 Member

    Does anyone know if Beyond has an option to lock scan rates to frame rates (or vice-versa)? Sort of like toggling maintain aspect ratio when resizing something in a graphics program.
     
  6. m0f

    m0f Member

    I'm fairly sure the issue is a result of the fact that lasers are vector scanned rather than raster scanned and the fps changes with complexity of the projection. There is a feature in Beyond that from the label appears as if it should do what you're looking for, however I didn't have any luck with it in my limited testing.

    Under the master tab on the right, scroll down to the very bottom. There is a feature called TV Mode - FB4 FPS Synchronization, with the option to set fps, frame repeats and time / phase shift. I haven't been able to find any reference to this feature in the documentation, however it appears as if this should allow one to lock the frame rate to match the camera.

    The only times I've had the issue is when working film shoots, and there's never time to properly test and tune out the issue other than the quick fix of adjusting the scan rate for the particular cue or sequence. On one particular gig I tried the TV mode - fb4 fps synchronization feature but did not have any immediate luck with it, and so had to abandon it for manually tuning the scan rate instead as everyone was waiting on me. So I'm not really sure it works as intended, or for that matter if this is really the intended purpose of the feature.

    The issue seems to often be very noticeable with pro cameras but not so much with lower end consumer cameras, for example I don't get any banding at all with either my gopro or my iphone, which makes it difficult to test the feature at home. I believe it's related to the speed of the sensor and aperture settings, and while a better camera / lens combo may capture a nearly instantaneous moment in time for each frame, a lower end camera can take almost the entire frame duration to absorb enough light.

    Miles
     
  7. base851

    base851 Member

    Hi Miles,

    You pretty much hit the nail on the head. I wasn't aware of the FB4 fps synchronization, but I have FB3s, so I'm not sure if it will work... worth a shot though. And I was using a Sony PXW-Z150, which would seem consistent with your observation on high end cameras.

    One thought which came to mind was to possibly use a synthesized image to double up the cue so that (theoretically) one "layer" would mask the others' banding... assuming the two layers would run on a slightly different time rotation. Of course that strategy could also bring your projector to a crawl on complex cues... so it might require using two.

    That's about the only other thing I can think of so far.
     
  8. Bob@Pangolin

    [email protected] Staff Member

    You might want to read this: Link
     

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