moving lines in the video. is this interference?

dirtyvu · Aug 8, 2017

So I was recording some video at a wedding outside of a church. And there were lines moving downward on the video. Is this interference? is there anything to counter it? I wasn't standing far from the drone at all. Maybe 20 feet.

I can upload some video later (kind of busy right now).

I already have the SOLO V.2 Long Range Kit 10.5dBi antenna (SOLO V.2 Long Range Kit 10.5dBi - FPVLR).I plan on buying 2 amplifiers (FPVLR 3W Bi-Directional Amplifier 2.4Ghz (compare with sunhans): Sunhans 2.5W Bi-Directional Amplifier) and 1 battery (12V dual lead battery 3000mah with charger: 12V dual lead battery 3000mah with charger)

Dmitry · Aug 8, 2017

You need to put a filter on the GoPro, depending on the illumination. If it's a sunny day then ND 16 or 32.
I put ND32

Dmitry · Aug 8, 2017

GoPro Frame2.0 - Professional Filter 6-Pack
BlurFix Air Professional 6-Pack
The camera will have to be balanced with the filter

dirtyvu · Aug 9, 2017

it most definitely is not a filter issue. I'm a photographer (I shoot with a Canon 6D, 5D Mark 3, and T5i) and I've never experienced anything like this. It looks like a VCR line that moves down the screen. I'll post a video when I can.

just_bruce · Aug 9, 2017

It's most likely prop shadows. The sun throws shadows of the moving props on the sensor of the GoPro

Joe Horn · Aug 9, 2017

dirtyvu said:
it most definitely is not a filter issue. I'm a photographer (I shoot with a Canon 6D, 5D Mark 3, and T5i) and I've never experienced anything like this. It looks like a VCR line that moves down the screen. I'll post a video when I can.

Strange to tell, it IS a filter issue. More precisely, it is a common drone-video problem that can be solved by installing a filter. As just_bruce suggested, the lines that you see moving down the screen are a stroboscopic effect caused by the interaction between the timing of your camera's video frame rate and the moving prop shadows. The length of exposure per frame also plays an important role here. Have you ever seen old movies with wagon wheels that seem to be standing still or moving backwards as the wagon moves forward? Or airplane propellers that seem to be moving at an impossible speed? That's the same stroboscopic effect at work. Installing an ND filter on your GoPro forces the camera to take a slightly longer exposure per frame, which causes rapidly moving objects to get slightly blurred, which is exactly what you need to do. Currently, each passing shadow gets imaged sharply, and strobes in time with the video, resulting in the "lines" you see on screen. If you blur those shadows with an ND filter, the strobing either becomes less noticeable or disappears altogether.

It almost sounds like magic, and it surprised the heck out of me when I learned it here almost 2 years ago. But I tried it and it works perfectly, and have been using ND filters ever since. My only worry originally was that the whole picture might get blurred... but that doesn't happen because the rest of the picture isn't moving rapidly. An ND filter also has the great side benefit of reducing the GoPro's propensity for overexposing highlights.

Try it. I promise you'll get the result you're looking for.

dirtyvu · Aug 12, 2017

but the propellers are not visible in the video. I can tell when the props are visible especially during severe movements. I have never ever seen the propellers with the drone just hovering.

andrew.baker.142 · Aug 12, 2017

dirtyvu said:
but the propellers are not visible in the video. I can tell when the props are visible especially during severe movements. I have never ever seen the propellers with the drone just hovering.

It is the prop shadows on the GoPro lens. You don't need to see the props to get a shadow.

Joe Horn · Aug 12, 2017

Andrew is right. It's not the propellers that are strobing; it's their shadows. Here's a video (which I did NOT make) that explains it well. No need for software repairs; avoid the problem by installing an ND filter on your GoPro.

Please note that the "flicker" in this video might look different from the lines you're seeing in your videos, but that's only due to the differences in angle and the interacting speeds which are causing the strobe effect. Searching YouTube for "prop shadows" and "prop flicker" reveals many similar videos, because it's a well-known problem.

dirtyvu · Aug 14, 2017

thanks. that was a great explanation. I'll try out the ND filter. Not sure how effective it'll be based on experience with a DSLR with filters. Filters were only really useful when at 90 degrees.

DJMc · Aug 14, 2017

It's not the polarizing filter that you you need in this case particularly.

Many of the filter sets have polarizing and non-polarizing version for each ND. As you say, using polarizing filters effectively is trickier in a aerial video when you're likely to be panning or transiting such that the angle of the light on the polarizing filter is harder to manage.

The higher ND filters alone are needed to increase the exposure time as mentioned earlier, and do indeed blur out the shadows. It defianately works [emoji5].

dirtyvu · Aug 14, 2017

Dmitry said:
GoPro Frame2.0 - Professional Filter 6-Pack
BlurFix Air Professional 6-Pack
The camera will have to be balanced with the filter

So how do you balance the camera with the filter? Does this mean adjusting the gimbal?

Dmitry · Aug 14, 2017

dirtyvu said:
So how do you balance the camera with the filter? Does this mean adjusting the gimbal?

dirtyvu · Aug 17, 2017

last question about the filters... since a lot less light is coming into the camera because of the filter, are you making settings adjustments to compensate? or are all your image corrections done in post-production? I do my DSLR photos with filters in manual and do settings adjustments because I'd rather not do all the work in Lightroom/Photoshop/Premiere Pro

DJMc · Aug 18, 2017

That's kind of what the filter is making the camera do. The exposure time for each frame is longer, which is how the camera is compensating for the lower light level entering through the filter. The longer exposure is what you want to reduce the lines by introducing some blur to the rapidly moving blade shadows.

dirtyvu · Aug 18, 2017

DJMc said:
That's kind of what the filter is making the camera do. The exposure time for each frame is longer, which is how the camera is compensating for the lower light level entering through the filter. The longer exposure is what you want to reduce the lines by introducing some blur to the rapidly moving blade shadows.

I know I'll find out when I try all this out over the weekend. I'm just excited to know early. So to summarize, I don't make any changes to the GoPro and all work to the image is done in post-production?

DJMc · Aug 18, 2017

You could do no post processing at all and let the camera do the work....same as the point and shoot options in a DSLR in a way. It depends as for stills how much control you want to take.

This is a really good sticky if you want to get up to speed on GoPro options and settings;

https://3drpilots.com/index.php?threads/1657/

It's worth a good read and has lots of content from some very experienced people.

Joe Horn · Aug 18, 2017

dirtyvu -- Correct me if I'm wrong, but it seems to me that you are assuming that video taken with an ND filter will look darker, and will therefore need to be corrected in post. But that's not correct. Yes, the ND filter lets less light in, but the camera compensates by exposing each frame longer. The end result is video that looks just as bright with or without an ND filter. The only difference is that the slightly longer exposure (due to the presence of the ND filter) reduces or eliminates "prop flicker". No post-production work is required to compensate for the ND filter (unless you used too dark of an ND filter, of course).

dirtyvu · Aug 18, 2017

thanks for the info. I'm just used to doing everything in manual mode, for both pictures and video. A decent amount of preplanning for light conditions and camera orientation. I'd rather do good preplanning then depend on post processing to compensate for bad technique.