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Opposition effect: Hot-spot or glow "artifact"

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A few months ago I started noticing an unusual "artifact" (or so I thought it was) in some of the footage I captured.

What I noticed could be sumarized as a hot-spot on the video frame, which only shows under certain conditions and, for the most part it is almost unnoticeable (which made me believe I was convincing myself to see things that weren't really there), but other times it was definitely there:

(levels adjusted to help see the hot-spot)
IMG1.jpg

IMG2.jpg


At first I thought it could be some defect or damage on the video sensor, but I quickly discarded this hypothesis when I noticed the Hot-spot moved along the screen consistently when the Typhoon moved or yawed.

It kind of bugged me, but since it's rarely noticeable I soon forgot about it. However, I recently started noticing this "artifact" again on 2 different CGO3+ cameras, so I decided to figure out what was happening..

It turns out it has a very simple explanation and its extremely common, however as previously mentioned, for the most part it's almost unnoticeable unless certain conditions are met.

What we're watching is known as the Opposition Surge (aka Opposition effect, opposition spike or Seeliger effect). And yes, it is just what I was seeing: a bright glow or Hot-spot around the observers´ shadow.

The technical explanation is: the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer.. When looking in a direction directly away from the sun, shadows are hidden by the object casting them. The point opposite to the sun and the adjacent areas therefore appear brighter than elsewhere because they have more sunlit surfaces and less shadow. (source: Opposition Effect)

The only times you will get to see this interesting effect (on your aerial footage at least) is when you're looking directly away from the sun (hence at the aircraft's shadow) while flying over a rough surface; a uniform colored surface will make the effect more obvious.

This effect is nothing new and isn't exclusive to aerial imagery, (it is the cause for a full moon to be so much brighter than when its on any phase, it can also be seen from an airplane or during a regular day just by taking a picture at your camera's shadow)

Anyway, I decided to compile some clips where this effect is noticeable. Each clip is followed by an edited version with adjusted contrast to better notice the effect (it can be sometimes very very faint, but it is there after all)


Some of you must have already known about this, but I just wanted to share with you my recently acquired knowledge along with some real-life video examples.

It might be something worth considering when planning your aerial captures!

Greetings!
 

Murray Martz

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A few months ago I started noticing an unusual "artifact" (or so I thought it was) in some of the footage I captured.

What I noticed could be sumarized as a hot-spot on the video frame, which only shows under certain conditions and, for the most part it is almost unnoticeable (which made me believe I was convincing myself to see things that weren't really there), but other times it was definitely there:

(levels adjusted to help see the hot-spot)
IMG1.jpg

IMG2.jpg


At first I thought it could be some defect or damage on the video sensor, but I quickly discarded this hypothesis when I noticed the Hot-spot moved along the screen consistently when the Typhoon moved or yawed.

It kind of bugged me, but since it's rarely noticeable I soon forgot about it. However, I recently started noticing this "artifact" again on 2 different CGO3+ cameras, so I decided to figure out what was happening..

It turns out it has a very simple explanation and its extremely common, however as previously mentioned, for the most part it's almost unnoticeable unless certain conditions are met.

What we're watching is known as the Opposition Surge (aka Opposition effect, opposition spike or Seeliger effect). And yes, it is just what I was seeing: a bright glow or Hot-spot around the observers´ shadow.

The technical explanation is: the brightening of a rough surface, or an object with many particles, when illuminated from directly behind the observer.. When looking in a direction directly away from the sun, shadows are hidden by the object casting them. The point opposite to the sun and the adjacent areas therefore appear brighter than elsewhere because they have more sunlit surfaces and less shadow. (source: Opposition Effect)

The only times you will get to see this interesting effect (on your aerial footage at least) is when you're looking directly away from the sun (hence at the aircraft's shadow) while flying over a rough surface; a uniform colored surface will make the effect more obvious.

This effect is nothing new and isn't exclusive to aerial imagery, (it is the cause for a full moon to be so much brighter than when its on any phase, it can also be seen from an airplane or during a regular day just by taking a picture at your camera's shadow)

Anyway, I decided to compile some clips where this effect is noticeable. Each clip is followed by an edited version with adjusted contrast to better notice the effect (it can be sometimes very very faint, but it is there after all)


Some of you must have already known about this, but I just wanted to share with you my recently acquired knowledge along with some real-life video examples.

It might be something worth considering when planning your aerial captures!

Greetings!
Well isn't that something. I usually try to read up on what is causing something, but you have nailed it dead on. Great post Jules.
 

FlushVision

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I noticed this effect almost as soon as I got my first UAS some years ago, and I've seen it on every UAS I've owned since then. Interestingly, It's more apparent on the Phantoms I've owned and no-where near as obvious on the H480, but still crops up occasionally on the H480.

I've always known about this phenomenon since starting flying UAS', but never knew what to call it. Now I do...thanks.
 
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That is very interesting. Yesterday was my 2nd flight with the TH (just purchased it recently). I noticed the hot spot in a gaggle of trees while flying away from the sun late in the afternoon (sunset was about 45 minutes later). I thought the camera housing had an opening where the lens was picking up glare from behind.

Here is the video. You can see it around the 0:17 mark.

 

rdonson

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When these artifacts appear are you using any ND or PL filters? I wonder if video shutter speeds have any effect on these artifacts.
 
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Good comments about the Glory-Effect. Thank you.
I've noticed that the best and most interesting lighting is at about 90-deg to the sun. Unless, of course, you want to see the sunset/sunrise or other special effects. Shooting directly away from the sun is the worst because it often hides shadows that provide depth cues in the picture/video.
Concerning ND filters, I use them always for video in sunlight. The Glory-Effect is still there. Haven't tried the polarizing filter yet. Anybody?
 
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I know this thread is old, but fits perfectly for what I was searching for today (I do love these forums - you guys rock!)
So I have a beautiful prairie video, taken shortly after sunrise, and the opposition effect is distracting. Anyone have recommendations for removal? I'm using Premiere Pro, but open to other suggestions.
Thanks in advance.
 

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