The Naked Scientists

The Naked Scientists Forum

Author Topic: What could make my visual system see everything as green?  (Read 1167 times)

Offline thedoc

  • Forum Admin
  • Administrator
  • Sr. Member
  • *****
  • Posts: 511
  • Thanked: 12 times
    • View Profile
Barbara asked the Naked Scientists:
   we were about 2/3 of the way down the South Kai-bab trail at the Grand Canyon when what appeared to be green snow began to fall.  At that point, we noticed almost everything had taken on a green hue, including our skin.  By the time we reached the bottom, everything looked normal again.  What caused this weird phenomenon?
What do you think?
« Last Edit: 22/01/2016 04:45:45 by chris »


 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4704
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why did everything look green?
« Reply #1 on: 21/01/2016 11:19:18 »
Probably "colour fatigue" from travelling in a predominantly red environment.

The brain has a subtle colour balance mechanism that eventually makes skin look the same in either natural or artificial light, despite the ambient color temperature being very different. Colour transparency film used to be made (possibly still is) in different varieties for indoor and outdoor use because "true" rendition showed swans to be blue if you photographed them on a sunny day and looked at the slide indoors.

I think the brain looks for the nearest it can find to white in any scene, then adjusts its overall colour mapping to make it white. If the ambient light contains a lot of red and blue (as it does in the Grand Canyon and the Australian outback, especially on a cloudy day) the brain "adds green" to make the whitest thing look white. Now if you introduce a genuine white, and snow is the best there is, that will appear green until the brain readjusts.

The phenomenon applies to all colours and is important when designing instrument and control panels. I think the readjustment is particularly slow where the ambient is green-deficient. Our eyes are most sensitive to green light and don't perform as well when it is absent. I find driving in Australia very tiring because the outback rocks are red and deep blue with little or no green, so my eyes are continually changing focus to correct for the chromatic aberration and the scenery always looks fuzzy.   

After you have been in the snow field, or even seen recognisable patches of snow for a while, your brain will have recalibrated to true white and your skin would appear normal again.
« Last Edit: 22/01/2016 04:47:01 by chris »
 
The following users thanked this post: chris

Offline alysdexia

  • Sr. Member
  • ****
  • Posts: 121
  • Thanked: 3 times
    • View Profile
Re: Why did everything look green?
« Reply #2 on: 21/01/2016 14:47:42 »
What do these pink comments do to you?
 

Offline RD

  • Neilep Level Member
  • ******
  • Posts: 8125
  • Thanked: 53 times
    • View Profile
Re: Why did everything look green?
« Reply #3 on: 21/01/2016 16:11:11 »
What do these pink comments do to you?

The colour of "Kaibab  trail at the Grand Canyon" is more saturated ,
( and would occupy more of the field-of-view , & viewed for a longer period of time ) ...


https://en.wikipedia.org/wiki/Afterimage
« Last Edit: 21/01/2016 16:15:32 by RD »
 

Offline alancalverd

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 4704
  • Thanked: 153 times
  • life is too short to drink instant coffee
    • View Profile
Re: Why did everything look green?
« Reply #4 on: 21/01/2016 17:01:23 »
There's also a rare possbility of actual green snow or hail, if a tornado picks up algal water and carries it above freezing level.
 

Offline Colin2B

  • Global Moderator
  • Neilep Level Member
  • *****
  • Posts: 1914
  • Thanked: 123 times
    • View Profile
Re: Why did everything look green?
« Reply #5 on: 21/01/2016 17:10:44 »
A friend of mine had a problem on Mt Kilamanjaro, altitude sickness caused him to see with a green cast. He improved when he went downhill (so to speak).
For the red hues of the Grand Canyon I favour Alan's suggestion of colour fatigue.
 

The Naked Scientists Forum

Re: Why did everything look green?
« Reply #5 on: 21/01/2016 17:10:44 »

 

SMF 2.0.10 | SMF © 2015, Simple Machines
SMFAds for Free Forums