 Poster: A snowHead
|
Megamum,
| Quote: |
Would the same flat light conditions result in an un-defined piste if the snow was a uniform colour other than white - say red, orange or blue?
|
Yes I think it would.
You would still have a lack of contrast; so instead of a lack of grey levels, which after all is what "flat light" conditions are (more grey levels = more contrast), you would be dealing with orange levels or blue levels etc......
|
|
|
|
|
|
Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
|
|
What think the cognsenti of: Will wearing a -admittedly powerful - headtorch during a daytime of flat light help get some shadow depth/definition?
|
|
|
|
|
|
Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
|
JimW, no - even then the amount of ambient light is orders of magnitude bigger than you would generate with one. Drive with dipped headlights in the daytime (with no fog) and you will not see a significant increase in brightness of the road ahead of you.
what you need is sonar!
|
|
|
|
|
|
You need to Login to know who's really who.
You need to Login to know who's really who.
|
|
halfhand, There was a 'think' in there, any other thoughts on that folks please?
|
|
|
|
|
|
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
|
Ah well.
PS shouldn't the thread title have a question mark?
Duck and cover...
|
|
|
|
|
|
You'll need to Register first of course.
You'll need to Register first of course.
|
JimW, I've a sneaky suspicion it did before it was 'got at' 
|
|
|
|
|
|
|
|
| stoatsbrother wrote: |
what you need is sonar! |
A bit like this. 
|
|
|
|
|
|
|
|
| Quote: |
| laundryman, I think you are locating perception at a different level from me. I'd see it after visual processing - a description of conscious awareness of a pattern. Where as you seem to be locating it at the level of detection by the eyes? |
stoatsbrother, I don't think I perceive perception differently. 
Photons are collected at the retina to yield intensities (in a few wave bands) across a range of solid angles. These "measurements" are then analysed, to create a model of the actual landscape in the brain of the beholder. The brain will always struggle to do the analysis if the initial "measurements" have a low dynamic range and, in particular, few or no discontinuities. This is what happens in flat light, IMV. The analysis can also go wrong all by itself, even with a scene of high dynamic range, and sharp edges, if an unusual scene has the some of the same characteristics as a more familiar one (such as the chequerboard illusion that's been presented here a couple of times). But I'm not convinced anything like that is occurring in flat light. The eye/brain combination is not perceiving phantom features, it just has difficulty extracting (perceiving) the real features from the poorly modulated signal.
|
|
|
|
|
|
You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
|
|
halfhand, I don't think so, there's a reflectivity/absorbtion thing going on. The problem isn't the colour of snow, it's that it's frozen water and light/water have interesting interactions.
|
|
|
|
|
|
|
|
| halfhand wrote: |
Megamum,
| Quote: |
Would the same flat light conditions result in an un-defined piste if the snow was a uniform colour other than white - say red, orange or blue?
|
Yes I think it would.
You would still have a lack of contrast; so instead of a lack of grey levels, which after all is what "flat light" conditions are (more grey levels = more contrast), you would be dealing with orange levels or blue levels etc...... |
Interesting... Perhaps green, the human eye has near twice the capacity to see green hues than red or blue.
|
|
|
|
|
|
snowHeads are a friendly bunch.
snowHeads are a friendly bunch.
|
Yeah come to think of that it's more than likely bollix - 4 pints and half a bottle of wine 
|
|
|
|
|
|
And love to help out and answer questions and of course, read each other's snow reports.
And love to help out and answer questions and of course, read each other's snow reports.
|
Low light levels are not the cause of flat light. Bright moonlight, with a tiny fraction of the light around in flat light, has plenty of definition. The eye can accommodate to enormous variations in light level.
| Wayne wrote: |
PS
It’s got nowt to do with shadows – that’s to do with perception and not flat light |
This is plain wrong.
Flat light is a problem because it causes a problem of perception and the scattering you mention is not the main thing happening in clouds.
In flat light all wave lengths of light are being reflected (and refracted) and re-reflected (and refracted) all over the place by (and in) tiny water droplets in the cloud and so almost none of the light is arriving direct and light is coming from every direction, so there are no shadows and the light seems flat.
There is also some of the scattering of light at short wavelengths that you mention, and this means that the effect is slightly worse at the blue wavelengths, and a yellow filter will make it easier to see the small amount of mostly yellow light that is getting through directly, without the bouncing around that is happening to most of it.
Skiing where there are trees not only gives you something to focus on to keep your balance (and indicate the general changes of steepness of the piste) but also blocks much of the light coming from some directions, allowing some definition of the contours by causing slight shadows and highlights.
|
|
|
|
|
|
|
|
|
|
|
You know it makes sense.
|
|
|
|
Otherwise you'll just go on seeing the one name:
Otherwise you'll just go on seeing the one name:
|
My answer was also about the physics (perhaps I shouldn't have mentioned perception but flat light is just our word for the light which does not cause shadows. Shadows are real and not just a matter of perception).
My point is that the kind of scattering you were talking about is quite different from the main effect of clouds which cause scattering of light by reflection and refraction by and in water droplets. This happens to all wave lengths, not just blue.
If the main effect were the type of scattering you talked about (caused by the actual wave length of short-wave lenght light being comparable to the size of the particles getting in its way) you would still see most of the shadows - there would just be an omni-directional blue light so the shadows would look very blue and the direct sunlight would be yellower (this happens to some extent with normal sunlight). There would not be a problem of flat light.
(Also you got wavelength and frequency muddled)
Last edited by Otherwise you'll just go on seeing the one name: on Wed 6-10-10 11:57; edited 3 times in total
|
|
|
|
|
|
Poster: A snowHead
|
|
Have not read the whole thread, but what is the explanation for why contrast is better near trees in flat-light conditions?
|
|
|
|
|
|
Obviously A snowHead isn't a real person
Obviously A snowHead isn't a real person
|
| horizon wrote: |
Well since you suggested it...is the cat dead or alive?  |
Both until you have a peek (but I always thought the Schrodinger was a nutter anyway), did he never think to just shake the box - if you shake it long enough you'll be sure it's dead
OMG - thread drift alert (sorry Megamum)
Last edited by Obviously A snowHead isn't a real person on Wed 6-10-10 11:45; edited 1 time in total
|
|
|
|
|
|
Well, the person's real but it's just a made up name, see?
Well, the person's real but it's just a made up name, see?
|
|
ulmerhutte See the end of my previous reply.
Last edited by Well, the person's real but it's just a made up name, see? on Wed 6-10-10 11:46; edited 1 time in total
|
|
|
|
|
|
You need to Login to know who's really who.
You need to Login to know who's really who.
|
|
The trees give a contrast item for the eye to focus on, allowing the brain to gague some degree of depth and perspective.
|
|
|
|
|
|
Anyway, snowHeads is much more fun if you do.
Anyway, snowHeads is much more fun if you do.
|
|
This thread has become only slightly more tedious than the one about the red jacket....
|
|
|
|
|
|
You'll need to Register first of course.
You'll need to Register first of course.
|
|
Dr John, sorry, but I only just read this thread and I couldn't let such a wrong explanation go, since it had been the uncontested basic explanation in this thread. Wayne was absolutely right about almost everything he said but it isn't the explanation for flat light. It is, however, the explanation of why a yellow goggle filter helps.
|
|
|
|
|
|
|
|
|
So if you would lose defintion if the snow was a different colour does flat light exist and act to remove definition from the ocean when you are at sea, you just don't notice it as you not wanting to ski down it? Wayne a bit of banter will only do this thread good - it's a dry subject otherwise - I took it as banter in the spirit it was offered, it was
|
|
|
|
|
|
|
|
Megamum, you don't lose definition if the snow is another colour.
It might be a bit worse in snow than at sea because there is lots more reflection of light off snow angled one way onto snow angled another, and anyway there are more indications of the surface in the sea, from foam etc. (AND you aren't trying to ski it.  )
Yes , there was nothing wrong with the tone of Wayne's explanation - I enjoyed the play-school type way of saying it. I just disagreed with his explanation.
|
|
|
|
|
|
You'll get to see more forums and be part of the best ski club on the net.
You'll get to see more forums and be part of the best ski club on the net.
|
|
The English owner of a small hotel in Untergurgl told me, some 15 years ago, that a certain branch of the British Army stayed at her hotel every year when they were practising skiing whilst blindfolded! Now that's what I call flat light!
|
|
|
|
|
|
|
|
FAQ
