15 replies to this topic

[skytiger]

In this picture of the sun, which is "shining", you can see many "radial streaks"
What is the name of this phenomenon? What causes it?
I believe it (like lens flares) is created inside the eye / camera / lens
because if I am wearing glasses they are much larger ...
I can't find any mention of it on the Internet!

[Chris_F]

I've heard it referred to as "temporal glare" with respect to computer graphics, though I don't know if that is the proper term for the physical phenomena. The explanations I read said it was due to particles in the vitreous humour of the eye.

[zacaj]

Is this it?
http://en.wikipedia.org/wiki/Crepuscular_rays

[Chris_F]

Is this it?
http://en.wikipedia....repuscular_rays

"God rays" are an atmospheric, not a lens phenomena.

[phantom]

The explanations I read said it was due to particles in the vitreous humour of the eye.

Particles in the vitreous humour, imperfections in the lens of the eye or the camera, basically anything which can distort the flow of light; the pattern depends on the imperfection.

[Postie]

Lens Flare is actually a combination of several different optical phenomena that occur because of the way lenses work.

Typically its either stray light that's entered the light gathering device from an odd angle or bright light from the scene that has been reflected/refracted back and forth inside from the front or back surface of the lens(es). These reflections can be quite sensitive to imperfections in the lens geometry or dust and atmospheric factors, and produce the differences you're seeing. I'm guessing the streaks are caused by light hitting the extreme edges of the lens.

[skytiger]

This document:
http://www.mpi-inf.mpg.de/resources/lensflareRendering/
seems to lump lens flares *and* "radial streaks" together - and refers to both as "lens flares".
To my human eye they are completely different, as I get streaks and not flares (when I squint at a torch)

[Hodgman]

The words "glare" / "bloom" / "flare" are often used to describe the same categories of effects -- ones that occur in the eye/lens rather than in the air.
However, "glare" is also sometimes used to describe a specular reflection...
Some useful terms might be: "bloom" / "lens flare" / "lens blur" / "shape blur" / "bokeh".

An easy way to tell if a phenomenon occurs in the air or in the eye/lens, is to simply place your hand between your eye and the light source. If the effect is still there when the light-source is occluded from your view, then the effect is ocuring in the atmosphere. If the effect disappears when the light-source is occluded, then the effect is ocuring in your eye.

e.g. haze or sun-dogs occur in the atmosphere, so hiding the sun behind your hand will not hide the "glowing effect", however the streaks and double-images in your first post are caused by imperfections in the lens system, so hiding the sun would also hide those effects.

To my human eye they are completely different, as I get streaks and not flares (when I squint at a torch)

That's because your eye is constructed differently than a camera lens, and doesn't contain the multiple layers of glass required to create inter-reflected flares
I've only skimmed that paper a few times, but I'd guess that you could use their method to simulate a human eye as well as the different types of camera lens that they demonstrate, provided you had enough information on the geometry and types of materials used in its construction.

[johnchapman]

As Chris_F mentioned above, the effect has been called 'temporal glare' (see this video and this paper).

I find it slightly unrealistic to see on a screen, perhaps because we're so used to seeing camera-type glare in films and games.

[Postie]

I've always found it hilarious that people find it necessary to implement lens flares in games, particularly FPS's. The implication being that in first person mode the eye of the player as represented in the game is an actual camera. 3rd person perspective or cut-scenes are a different matter though.

[skytiger]

Result! That has been bugging me for 2 years now ...
Thanks to everyone especially Chris_F and johnchapman
Hodgman: another way is to rotate your head - if the phenomenon rotates with it, like temporal glare does, it must be in your eye

[MJP]

I've always found it hilarious that people find it necessary to implement lens flares in games, particularly FPS's. The implication being that in first person mode the eye of the player as represented in the game is an actual camera. 3rd person perspective or cut-scenes are a different matter though.

Effects like glare and lens flares provide important visual cues as to the brightness of a surface when you're using an LDR display device.

Also I don't see why the perspective should dictate whether or not you simulate camera-based lens effects. Besides...glare happens in the eye too.

[Postie]

True, but nowhere near as much as happens in a camera lens. There's only one lens in the human eye, but camera lenses can have 5 or more lens elements internally. Even with anti reflective coatings and low dispersion glass there's still alot of surfaces for reflection.

What I was getting at with the perspective is that if you're playing in first person perspective, the view you're seeing is from the player's eyes, but in 3rd person you're watching yourself from an external viewpoint, such as a camera, not someone's eye. (In my opinion).

My "gripe" is pretty much a moot point, since the punters expect it in games these days and the bigger the better right?

[Labrasones]

This is getting more and more off topic, but the way I've always seen the sun glares is that there is a lens over the player's eyes. I mean, you have a HUD (In most FPS modern setting games) that implies some sort of lens or screen in front of the viewer's eyes. So I find that a sun glare makes sense. For games set in the past, or games with HUDs that look more drawn than digital, the lens flare can be explained away by glasses on the player. And then, like MJP said, flares give clues as to brightness, you can't stare at the sun after all, and you can't in game either.

[Nessa]

yea first I tho that was something about complex maths a geometry but its about the stupid sun

[mdwh]

I think one of the problems is that, even if a viewpoint is meant to represent "the player's eye", it can never represent bright lights realistically, with or without these effects. So I can see an argument for putting other cues to suggest the illusion of brightness, even if it isn't strictly accurate.

After all, the player is playing on a TV/monitor. And we all have experience of seeing the sun on a TV - firstly we don't expect that it's as bright in real life, but it does have the lens flares. I don't feel the fact that that implies a physical camera is a problem - it's about what people's subconscious perception is.