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When I read the feedback and conclusions from my earlier post here:

is there a way to clone and mirror at the same time in Krita?

it seems to me that an object reflected on a relatively calm water surface should appear approximately vertically mirrored, with all the caveats examined in the post.

So what about night lights, including the Moon(!), which, in most pictures I can find, appear in their reflection as very long streaks of light, much longer than their own purely geometric mirror image?

Some examples:

https://unsplash.com/s/photos/moon-water

https://www.fotocommunity.it/photo/portovenere-by-night-fabri-lunardi/33401002

I understand that the sea or a lake are never completely flat, and among all the infinite ripples there are surely some small sections of plane with the 'right' angle to pick up some light and reflect it even very far from the object's strict mirror image.
So OK, a very strong light will be picked up and reflected, in addition to within its mirror image, also at some isolated, small spots all along the vertical line of view below it. This I get, and I see it even in my own daylight photos.

But such a strong, almost unbroken streak below each and every city light, or the Moon?

Q: does any of you know how to explain this?

Is this the effect of some photographic trick, like long exposure, so that all the small lights are summed up and shown all together?
And if so, do you know where I could find examples of unadulterated photos of villages on the sea or on a lake taken at night?

[I understand that the obvious thing to do would be (or would have been) to go physically to a place like the one I am describing, at night, and observe what it looks like, or take my own photos.
True. I should have paid more attention when I had the chance, and right now I cannot go :(
But I am sure you can enlighten me :D ].


EDIT adding a night photo of my own

enter image description here

Taken with a smartphone, not even very good quality, surely no long exposure tricks or anything... and the lights look like long streaks!
Go figure...


EDIT 2 - more photographic evidence

When the water is calm (= flat), no streaks! So it all makes sense in the end!

https://www.google.be/maps/place/19032+Lerici+SP,+Italia/@44.0809296,9.9060377,3a,75y,90t/data=!3m8!1e2!3m6!1sAF1QipOOC_QjDI6cl39gK-m8ANtN8tKf6q5oiWzpMvO0!2e10!3e12!6shttps:%2F%2Flh5.googleusercontent.com%2Fp%2FAF1QipOOC_QjDI6cl39gK-m8ANtN8tKf6q5oiWzpMvO0%3Dw203-h152-k-no!7i4000!8i3000!4m5!3m4!1s0x12d5027e6a72c4cb:0x9a94f431d70c395f!8m2!3d44.0756332!4d9.9169337?hl=it&authuser=0

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  • Might be better answered at photo.stackexchange.com -- I'm wagering most of this is done in the camera or with multiple shots which are then composited.
    – Scott
    Jan 26 at 20:21
  • Thanks Scott, I might post there as well. But I am asking this in the context of digital painting, so people might be able to help here too. BTW I found a photo of my own at night, which I am sure I did not take with special equipment, and guess what... long streaks! This is weird. I will post it above. Jan 26 at 20:29
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    The "long streaks" are more about camera position as it relates to the object and its reflection.. it's a natural perspective thing. The farther you are away from the light-emanating object and the more distance the reflection can travel, the longer the streaks.
    – Scott
    Jan 26 at 20:32
  • As for how to "fake it with software".. well that's a deep dive and often photo, and software, specific.
    – Scott
    Jan 26 at 20:34
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    This is more of a physics issue rather than a graphic design issue. I found this related question over on Physics Stack Exchange.
    – Billy Kerr
    Jan 26 at 22:41

1 Answer 1

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The answer is Angles

Let me simplify.

When you are taking that kind of photo, the water is a horizontal plane, the camera is pointing horizontally and near the water.

enter image description here

Let me have an imaginary rope between the camera and the light. Let's call this the "line of sight rope" or "rope" for short.

enter image description here

Imagine now that we draw a grid, like a perspective grid on the water. Separating it into squares. What we would see is that even if the squares remain horizontally, the reflection already covers more squares under the "rope", than to the sides of it.

enter image description here

We would need to strongly rotate these lateral squares, to the inside in order to have a reflection of the light. Any rotation to the outside would produce no reflection at all.

enter image description here enter image description here

But only slight variations in angles, on the tiles under the rope.

enter image description here enter image description here

So that is the answer. We only need tiny waves to have the reflection under the rope to be noticeable. When we increase the distortion on the surface we start to see the with of the reflection increase, but this already has increased the vertical length of the reflection.

The lower the light is on the horizon, the more and more tiles under the rope will be part of the reflection. Kilometers and kilometers, but almost no change on the sides.

enter image description here

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