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Jello Question

Discussion in 'Phantom 2 Discussion' started by adanac, Jun 5, 2014.

  1. adanac

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    Can someone explain why jello only seems to happen when I shoot in bright daylight? I normally shoot in 1080/60fps. I'd like to understand this better. Please don't just post "get an ND filter" without some discussion.
     
  2. ladykate

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    Your props are shading the sun as they rotate. You camera is using a fast exposure rate which captures the shading. It causes a perceived flutter - which looks like vibration jello (sorta). Thus, the solution is to either fly away from the sun (can't in midday) or get an ND filter so the sync up of the shadows of the prop are spread out and not (as) noticeable.
     
  3. adanac

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    I'm not sure I agree an ND filter would help with prop shadow but let's not get off topic. I don't think it's prop shadow, I think it's jello.


     
  4. ladykate

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    You might be right in that you may still need to put a hood over the lens. There are a couple of YouTube videos that show the results of the ND filter wiping out the flutter. In one the guy put on a hood that shaded the top of the lens and that helped, too. However, you may still have jello. Your post gave a specific situation that is usually solved by decreasing the light so the camera slows down its exposure/hooding the lens.

    Bright light = jello/flutter? Decrease the light.

    If you would like to try that, you may find joy (or not). If it ends up that you still have jello, then do the normal things - balance the props and adjust the dampeners that you have. I noticed on my H3-3D that the white dampeners were not working well - going to the black eliminated a large amount of the jello.
     
  5. ianwood

    ianwood Taco Wrangler
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    To understand "jello" better, read this:

    http://www.diyphotography.net/everythin ... g-shutter/

    An ND is the only way to deal with it effectively. An ND might also help with prop shadows but I've seen prop shadows with the ND as well. The only way to truly keep the shadows out is to use a visor or not have the light source at angle such that it passes through the props before entering the lens.
     
  6. ladykate

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    I agree - I shouldn't have only said the ND filter would do it. I changed my last response to his post (made while you were making yours). The hood on the top of the lens might be necessary (someone made it out of simple manila paper and that seemed to work a treat).
     
  7. adanac

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    Thank you. I understand how a rolling shutter creates jello, I'm just not sure I understand how slowing down my shutter speed helps. I'm wondering if it would go away if I shot at 30fps instead. I also don't know which filter to get as I can't find any recommendations. Lastly, I would prefer a polarizer, which might also provide an associated loss of 1-2 stops.

    I only get it in bright daylight. At other times everything is rock solid (knock on wood) and great.

     
  8. ladykate

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    One problem I have with a polarizer is that it is heavier and requires you to adjust the filter so the light is properly polarized (rotate it). You can do that, with an HDMI hookup or cell phone app, but I've always felt it was too heavy a solution and too easy to accidentally move.
     
  9. ianwood

    ianwood Taco Wrangler
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    The higher the shutter speed, the more the rolling shutter is noticeable. If an object is in motion relative to the camera, a rolling shutter will distort the object proportionally to its speed. The shorter the exposure, the less the object's motion is captured making the distortion more noticeable. A lower shutter speed will blur an object in motion creating a smoother transition between frames making the distortion less noticeable.

    Reducing FPS may reduce shutter speed but not necessarily. You don't want to use a polarizer unless you are filming near water, snow or other highly reflective surfaces.
     
  10. adanac

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    I don't 100% agree about when to use a polarizer (I feel there are other times in addition to those you've listed).

    I understand the relationship between motion and rolling shutter, but I'm not sure if the read-out time of the sensor changes with shutter speed. I don't think it does but I admit I don't know for sure.

    I'm wondering if, in fact, I was just moving too fast in the shots I saw jello in. That is possible and will require more tests.


     
  11. ianwood

    ianwood Taco Wrangler
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    The sensor should always scan at full speed. When the shutter speed is slowed down, the sensor will make more top to bottom scans per frame (thus increasing exposure). More scans per frame will give you a more complete and smooth image as the object moves relative to the camera.
     
  12. adanac

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    Fascinating, thank you.

     
  13. shartlza

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    Here is a quick comparison video I did with my Polar Pro ND filter. http://youtu.be/5B_YdtVYRaM I did the pass descending forward since I noticed that always induced jello. I did the first pass with no ND filter and you can see the jello (on a computer screen). Then I landed it, put on the ND filter and did the same pass. You will notice with the ND filter there is no longer any jello. Also notice that the video looked richer and brighter. Both of the clips were edited with the same color profile. I have since balance the gimbal using the "Ianwood method" of putting some weight on the end of a paper clip (small screw with 2 small nuts) and then tapping it to the pitch motor with the weighted side pointing to the back of the craft. I got it perfectly balance, surprisingly better than factory since out of the box if fell to the pitch motor side.

    In was on $30 and in all honesty was well worth the money!!!
     
  14. adanac

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    Now I am having 2nd thoughts about this. :) Isn't jello the result of an object or objects moving too quickly during a single (not multiple) sensor read/s?


     
  15. maher

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    Jello are perceptible when there is a vibration creating high frequency oscillations of the camera around any axis. Because of the scan principle of the image acquisition of the GoPro camera sensor, straight lines looked wavy even when the Phantom and the gimbal are mostly still.

    This stroboscopic interference is dependent of the frame rate, the scan sampling process, the camera jitter. As in any sampling process, high frequencies components can traduce in apparition of undesirable low frequencies artifacts in the capture. The common remedy consist of lowering any high frequencies components involved prior to capture.

    The ND filter doesn't change the frequency of the rolling shutter, but by forcing the exposure time of each frame to increase it help averaging the wavy effect in a motion blur effect.