optical effect standing in front of venetian blinds

Factual Questions
1

I’m not sure how to describe this, nor do I have a picture that demonstrates it. but its been bugging me…
We have a darkened meeting room where the speakers will stand in front of closed venetian blinds. DIffused light passes through the slats of the blind.
There is a weird optical effect surrounding the person or object when they are silhouetted against this background.
The edges of their outline are “jagged” instead of smooth.

Is this an actual physical effect of the light diffracting through the slats and around the person, or is this a perception effect of my eyes and is essentially an optical illusion?
I think if I had a picture I might be able to get an answer more easily, but unfortunately, I havent’ entered the 21st century yet.

Can anyone answer this or perhaps at least link to an image that shows this effect?
On edit: here is an image of someone in front of venitian blindslike I describe, but the effect is not there. It could be that it is lit differently then the room I’m refering to

2

I’ve wondered about this myself. My WAG is that it’s just an illusion, with your eyes blending the dark parts of the blinds with the person.

3

I agree. It is not physical. The bright bits are just getting processed somewhat differently from the dark bits. It is probably not photographable.

Optical illusions that arise from actual physical effects are pretty rare. Most of them arise from glitches and compromises in the ways the visual system extracts information from the ambient light.

4

Your eyes determine the boundaries of an object by the contrast between it and the surrouding medium. If that contrast varies (because the surrounding medium changes, or part of the object is closer in shade to the background) your perception of that boundary will be discontiguous, and takes a bit of conscious effort to perceive the true boundary.

5

Just for the sake of “whatever” the next time you are in this situation close one eye and see if the effect improves, worsens, or remains the same.

I can’t think of a reason that stereo vision would be a factor but it’s one mechanical way that your vision and the photograph differ.

6

Already did it. It remained the same.

I was looking at a bald guy with the slats in the background, In addition to the ‘jagged’ edges around his head, I could see a thin dark line just hovering over his head with clearly a space between. As he moved his head up; the line would move down to join his head and be part of the jagged outline.

It seems a bit odd that an optical illusion would cause that floating line above him and join his head by moving down as he moved up. which is why I thought it might be actual physical focusing and diffraction of light.

ANyone else see this effect. I guess I’m not convinced it just physiological, though its very likely to be the reason.

7

Reflection? If the slats of the blinds were turned so that some portion of the curvature would diffuse light from the room in the direction of your eyes, the relative brightness of a bald pate would be a bright spot in the reflection, and one made more eye-catching by the movement (“as he moved up”).

If not that, I got nothin’.

8

Maybe it has something to do with the angle subtended. If the angle is narrow and the contrast bright, it might be enough to cause some sort of feedback or interference (for lack of better words) between neighboring nerves.

For example (and note there is not cite provided so maybe this isn’t accurate)

So changes that you wouldn’t think should matter might even if your situation wouldn’t be considered “bright light.”

Also, the nerves in the retina do a fair amount of pre-processing, not to mention whatever happens in the brain before a sensory stimulus rises to the level of consciousness.

9

Here’s an image I found that I think is what you’re talking about.

Thumbnail photo of thing in front of Venetian blinds – Notice the jaggies.

The jaggy illusion is not very apparent in the full-size photo.

10

the jaggies I think are caused by the black drop effect (the little dark bridge that connects two dark things before they touch, try to move your fingers close together without touchinge in front of a window to see it). I think it’s mainly caused by diffraction and blurring by the air/your eyes

11

If I understand the OP correctly, I believe this effect to be mostly physiological. Your eyes and brain don’t work much like film at all. We have a much greater range in vision under more extreme clashes of intensities of light. Still, our cornea, lens, vitreous fluid, retina and fovea all add imperfections in resolving “over/under-exposure” in our center of vision. There’s going to be some amount of diffraction and diffusion. On top of this, I think your brain is creating an optical illusion due to the way our brain interprets the contrast of patterns, and can “merge, blur or bend” absolutely demarcated areas of contrast as seen in this illusion.