I was looking through last years ski photos (man ,can’t wait for the snow!), and I noticed that the shadows are all the same-a deep blue color.
Why is this? Even changing the saturation doesn’t alier it-shadows on snow are blue.
Yet shadows ob light/white sand are gray-why is snow different?
The sky is blue, and much of the sky is still illuminating shadows. If the colors are balanced so the snow is white when it’s in the Sun, it will appear blue in the shadows when only the sky is illuminating it. The snow doesn’t have an intrinsic color, it’s just scattering the incident light.
I believe that the shadows in snow are a case of multiple scattering. the blue of shadows isn’t the same as that of the sky.
The blue of snow seems to me very similar to the blue color of light diffusing through ice, as in the case of the (now disappeared) Paradise Ice Caves. Certainly, in that case, the color owes nothing to the sun.
The blue of the sea is another case of multiple scattering, but the process is somewhat different, and the blue of the sea is much deeper.
Blue scattering from the sky is certainly a major component. I recall a few years ago here on the dope we had a discusion regarding whether the sun was “white” or “yellow”. I got tired of the sillyness and did an actual experiment.
I took a white piece of paper. I put it in our closed up garage. The one small window has a blind on it. I took a aluminized telescope mirror, placed it outside and reflected the sun through a small space in the blind to form an image of the sun on the piece of paper in the otherwise dark garage. I took a picture with a camera. That piece of paper was only illuminated by the sun (no sky). It looked yellow to my eyes right off the bat.
Then, I took that piece of paper and placed in the front yard, where it was exposed to all that blue sky. I cast a shadow on it and took a picture of the shadow area. That area was only being illuminated by scattering from the blue sky.
On the computer it was obvious one was more yellowish and one was more bluish. Going further and using some image processing software, you could see that there was signifcantly more light in the blue channel for the shadow photo than the sun only photo.
So yeah, if your camera is set to make the snow in the sun look “white” then the shadow areas are going to look “bluish” from the blue sky.
Did you use a digital camera? Auto white balance will adjust the color and not always produce a true rendering as the eye would see the scene. This is true of photo labs processing conventional film prints as well. So I’m not claiming you are wrong but I am wondering whether you controlled the variables enough to call this an experiment.
Also, a point in a shadow is not illuminated only by blue sky. Sit in a shadow and look around. The reflected light off everything you can see is illuminating you.
Yes I had auto white balance OFF. And the piece of paper could only “see” the sky.
Oh, it occcured to me last night you could do similar experiments with a box full of snow and figure out how much of the blue is from sky and how much is from internal scattering within the snow itself. But given we only get snow (and usually only once) around here every 5 to 10 years it might be awhile if you want results from me. One of you more nothernly folks is gonna have to take this one.
I might nitpick and say that illumination from ‘the sky’ is of course also from the Sun; it’s just sunlight that’s bounced off of air molecules. But the effect is the same: since the air deflects blue light better than yellow, the indirect sunlight is blue compared to the direct sunlight.