Challenge Questions

This would have to be a pretty dark blue. After walking 50+ years in snowy Minnesota I haven't noticed any shadows on the snow that are noticeably blue.

I don't believe I am colorblind.

It depends both on where the shadow-light is coming from (reflected off hills or the sky) and on what else you can see at the same time. If you see the shadow mainly against sky it will tend to appear more dark-grey (this is because to a large extent the eye judges colour by what it contrasts against)

There is some background criteria to support this. If you have ever gotten involved in the wild wonderful world of photography, you know where I am coming from. The atmosphere tends to be a Blue-Green filter and thus the outside ambient light tends to be just that. Most film sold (of course with digital not much gets sold) is what is called "Daylight Film" and is corrected for blue-green to enhance the reds and yellows. If you shoot Daylight Film indoors without a flash it comes out red, since tungsten light is quite red. Our eyes and mind automatically adjust our preception to account for the different base colors, but for photography, the film has to be formulated for the adjustment. That is why they also make "Tungsten Film" which corrects to enhance the blues & greens.

Now being as the Daylight color shifts bluish, that would account for the blue hue to the shadow as it becomes more prominent, but in actuality all daylight is blue-green.

A shadow has no color as it is an absence of light. The blue, purple, yellow (don't eat) or whatever color perceived is ambient light reflecting off the background, not the shadow itself.

I don't have a shadow, I'm staying inside!

I agree with post 1 that it is blue. My explanation is that the area of the shadow is illuminated by the blue light scattered from the atmosphere (since the white/yellow direct light from the sun is blocked) which is in turn reflected from the snow in the shadow making it look blue.

The light in the shadow is not just "scattered from the atmosphere". The sunlight hitting outside the shadow refracts around in and through the snowbank. Similar situation noted during winter bonfire parties.

Cheers

In my humble opinion it's gray for ideal atmospheric conditions. For subtractive model of color the reflection of white snow is perceived as "white" due to the one reflects all spectrum of visible light uniformly. It means that dropped shadow is the reflection of the same set of light spectrum but someway weakened in its amplitudes. That means it's gray.

to continue my reasonings, I would even suggest that color of shadow over snow surface is white. Simply its whiteness is less intensive.

I'm singing the blues with BobD.

The light falling outside the shadow includes the yellows greens and reds from the sun. The light falling inside the shadow is primarily the scattered light from part of the sky, which is blue. This is of course more marked in areas where the ground is flat (as the illumination in the shadow would not then include light scattered from the remainder of the ground).

I'm curious what makes snow determined as a white here or there? Is it remaining as a white in twilight conditions?

Shadow can exist being dropped upon some object only and I thought that its(shadow's) color coincidences (in some measures) with object's color. If there would be a green grass background instead snow, shadow gets a green color's hint respectively.

Perhaps the problem is that we use 'colour' descriptors both for a material (e.g. "silver screen") and for the colour projected onto that material (coloured motion picture)?

So, I agree that the snow is white as it scatters all colours more-or-less equally (albeit it often has an almost imperceptible blue tinge).
But shine a blue light on a sheet of white material and the sheet will appear blue. So, if we have a white surface, and shine white light (sunlight+skylight = white) on part of it but shade some other section, the shadow will be the same colour as whatever light is falling onto the shaded area; in this case the light in the shadow mostly comes from the sky, which (on a clear northern day) should be blue.

Fyz

Snow, like water, doesn't really have a color

so any color it appears to have is a function of what it is reflecting (clear, sunny day) to my feeble mind meant pale blue.

I'm not so sure snow doesn't have any colour.

My shadow has no color of its own. It is representation of my image do to the light that I block. The snow would have the same color just not as vibrant in that area.

i think its depends how suuny is outside? if more, then the shadow will be darker (gray) if less, then more grayish ...

regards

Waz

It would be Blue

I agree with 1, 3, 7, 9, and 11 that the shadow would be blue. Others who have suggested that light scattered off other objects is the area (green vegetation, your own clothing, etc.) will also impact the color are correct, but since the blue sky more or less fills one hemisphere of the scene, the answer is still blue.

I am sitting in a room with a floresent light source. I have a white paper plate on my desk. When I hold my finger over the plate to cast a shadow it appears gray until I get close enough for the white surface to illuminate my finger. The shadow at that point appears to take on the color of my flesh although faded a bit by the gray background. Based on that I would say gray with the possibility of some color nearer your feet depending on what you are wearing.

....and similarly ........

The shadow of your finger is gray. The shadow of your body which covers all paper surface would be considered as white :).

TIC

#'s 1-23 discuss a curious unknown thingy..........please describe snow so I may try to understand these trying issues referenced....................

SOUTHERN CALIFORNIA BORN AND RAISED.

'Bout 70 Degrees now...10:00 AM......may have to turn on the AC.

[EAT YOUR HEARTS OUT, GANG.........a cold sudsy glass 'n chips would go great for a snack]

MR. GUY

In your case - substitute "sand" for "snow"

Describe what is it like? Umm.. Just open your fridge ... :).

Going further on the fluorescent light topic, have you ever taken a photo (Without flash) under fluouro lights? Everything looks green. Yet we see normal colours. So I'd go along with the blueies...the shadow will be predominantly illuminated by the blue sky, so will have a bluish tinge, though we will probably not percieve it as such.

Now go near the window on a clear day with the sun obscured by the house. Shade a section of the paper from lamplight but let skylight fall on it. What colour do you see in the shadow?

Last weekend, I photographed some of my girlfriends horses. It was a sunny day with some snow cover. The shadows on the ground definitely came out blue.

I also vote with the first comment, the shadows are blue.

Y'know

actual experimental eveidence has screwed up more good theorys thru the ages.

And it hasn't always gone well....

Photographs may not represent snow correctly. Anyone who has worked in a darkroom knows how difficult it can be to make snow appear white on a photographic print - as it tends to come out purple. Also with digital photography, your camera is often using image processing to color correct the image to make images appear the "correct" color.

So, this being said, a photograph will not prove that the shadow is any given color as variations in film processing and/or digital image processing will result in different colors. (I've even had green snow from cheap pharmacy processing.)

If I had to speculate, I would say that a shadow itself has no color. (I think this meant to be a trick question.) If in the question you are asking "What is the color of the snow in the area of my shadow?" I would lean toward the blue answer. This is due to the atmosphere reflecting blue light around in itself. (This is why the setting sun appears so deep red - it passes through more atmosphere to reach you and the blue light is filtered more so than when the sun is at high noon.)

So the bouncing/reflecting blue light would illuminate the snow in the parts that are blocked from direct sunlight. Thus we would have a blueish shadow. I think. . .

Agreed with photo and anything solid media out printing. As former worker in printing press field I can say there are a lot of tricks how to "cheat" innocent customer due to known handicaps in color reproduction. For CMYK model - cyan is the hardest color to reproduce correctly, magenta is more or less available, yellow - is the best for reproducing. White (background) has a ton of hints. Hexachrome(6 color) model is more advanced but not an ideal as well.

I agree, all types of photography will not always display colors correctly. However, in this case, that's pretty much what I saw, but not as distinct. In actuality, under oath, I have to say, more gray than anything.

You would see gray because the eye is overwhelmed by the bright white snow. The pupil reacts to this, and contracts to reduce the light level. Under these conditions the cones (color sensing cells) are starved for light, and cones don't work well in low light. Virtually all the information available to your visual cortex regarding the small amount of light reaching your eyes from the shadow will have come from the rods which are not sensitive to color. So you see gray. But it's still blue (reflected from the blue sky). Any self respecting spectrometer will tell you that.

Was it a clear sunny day, and is the ground flat? We also need to be well away from dawn or dusk, and if there was even even a modest amount of cloud or there is snow on a hill that can reflect into the shadow, grey is expected. (I suppose that means that the question wasn't sufficiently specific to allow a unique answer?)

I'd use here as I call it "presumption of max simplification" for nothing said against that. That is absolutely plain surface of absolutely pure white snow, cloudless (sunny) day, 12 pm or so time etc. Otherwise it would be endlessness of nuances to discuss. By the way you've said at this thread that body (of human beings) is not absolutely opaque. Yes, but isn't it presumed a lot of clothes should be worn for winter conditions?

I didn't think of it at the time, but what animal could have possibly made those paw prints in the snow? The photo was taken at work, a hugh military industrial complex, spanning over one square mile, behind razor wire. The snow is about 36 hours old, so somewhat modified by the sun. Definately not a dog or cat. We do get a lot of skunks around, but I thought they hibernated. Perhaps a racoon?

Kind of hard to tell, but I'd guess coyote. Too far apart for skunk, and unless there was a lot of edge melting, too big as well. And the pattern doesn't look at all like a 'coon. Did you see any detail of the toes?

Yes, I didn't think of it, but a coyote makes perfect sense. The tracks were subject to an entire day of sun, so no detail.

We had a "shop cat" that the guys were feeding. He showed up all beat up one day. We took him up to Tuft's, and they put him down. I think, only a coyote could have done such damage. But you never see them, ever. Why they would come in here, I don't know. Perhaps, a food source of garbage.

"...Why they would come in here..."

Because it's a protected area. Nobody messes with them, there's probably a lot of undeveloped land with a good population of mice, voles, and rabbits (primary food sources), and so the livin' is easy. Coyotes have proven remarkably resilient in adapting to live around humans.

Obviously a blue mylar cutout he photogrametricized.

Hey, wait a minute, I feel.......violated.

Don't take it personally...........

That won't stand up in court

I was not wearing any coat at all, just my work uniform, (arc-flash approved). I think it's a perspective thing. The photo was taken with my cell phone, held maybe 1 foot from the bottom of my chin. As, of course it has no viewfinder, and I must hold it close enough to my face so that the screen will be in focus with my reading glasses.

I suppose there are other reasons the shadow could have a purple tint, other than the above stated photography issues. The uniform is dark blue, and it could be a secondary reflection off of it.

Maybe here's a distortion of monitor color profile but I don't see a bit of purple. Dirt gray mixed with blue. Sorry. It seems a cause is in my monitor(videocard) features.

I concur with Ozzb that technically the shadow has no true color of its own. However, as Bricktop has shown, it has the appearance of being purplish-blue. Is having an appearance of something the same as actually being something? What is the color of the back side of a rainbow?

The color of any body is what that body reflects in terms of light spectrum. If body's color is red it means that one absorb all white light (white noise if you like) spectrum unless the red (100% yellow + 100% magenta). It's a core of subtractive model of color. Rainbow along with what you see on your PC monitor is a sample of additive model of color. So back side of rainbow believed to be the same.

Happy new year and Merry Orth Xmas, Enviro!

Thanks, Caramba, Happy Holidays (ex post facto) to you, too! If you want to know the color of the back side of a rainbow, next time you see one, just walk around it and see for yourself...

Itsa same as the front side with the sun shining in yer eyes 'an no colours.

HOWEVER>>>>>>>>>>>>>what if you happen to be standing at the exact spot (no, no pot of gold nonsense now) where it's emanating from?

Since it emanates from the prismatic effect on (sun)light created by water droplets, then it would be water off a duck's back, so to speak.

Blue, blue, blue!!!!! However, as the sun goes down it will start to turn purple!

First, let me qualify myself. I spent 48 years in the Dorchester section of Boston, Massachusetts.

When ther was snow on the ground, I never did see a shadow. Even late in the afternoon, when there is snow on the ground, there is so much reflectivity the shadows have no place to propagate.

Well that is just a silly comment to make. There are shadows....even in Boston.

I just spent the day at kirkwood chasing my BLUE shadow down the mountin numerious times. Funny thing weather staying up on the Board or off the Board and Rolling down the mountain, I never did seem to catch that darn shadow, but I saw the blue in its eyes.

I would agree with your viewpoint regardless of I belong the opposite party here. Really given for instance the only source of light and absence of any affecting factors (additional sources of light, refraction atmosphere effects etc) we must get absolutely black color of dropped shadow. Any one can recall shots taken from space.

One of Photoshop design technique for realistic shadow dropping is presuming drop absolutely black shadow from object onto background, then apply blur and transparent filters. Its one more indirect confirmation of shadow blackness.

I'd rather agree with you completely if you'd state that color of shadow is absolutely black.

Isn't the shadow, in itself, every colour that it doesn't reflect ?

There's something very wrong with that picture these days.

Very probably (but note Poisson's spot and Arago disc in the centres of the regions of solid shadow)

To all practical intents and purposes, I agree that the shadow o fthe human body is black (and that is all that matters for realistic visual visual modelling). However, on the pedantic basis I warned about, first-order is correct.

There are two reasons for this:
. The first (and more significant) is that the human body is not completely opaque; you can see evidence of this when you close your eyes and face towards the sun - you see orange-red light penetrating your eyelids. Similarly, bones are more scatterers than absorbers, so light will penetrate them as well.
. The second (and fundamental) is that light diffracts round the edges of your body. Either the fact that the sun subtends a finite angle or that visible light covers about an octave is then sufficient to mean that the only (again purely hypothetical) way to achieve true blackness at any point would be to entirely surround the region of interest with a perfectly opaque screen.

P.S. Am I right that Photoshop is just a retouching system (as opposed to a visualisation package)? [A visual modeling package should automatically fill shadows with the expected light from other sources rather than using blurring or semi-transparency]. On the other hand, I would not expect a visual modelling package to routinely generate either Airy patterns or Poisson's (bright) spot (alternatively the Arago spot).

It's only one of Photoshop technique, which used to be applied by average photoshop artist/operator to make shadow look more or less real. I did not mention complete automatic filtering. By the way, it's not a problem for trained eye to notice artificially dropped shadow. If we consider practice of a real artist, shadow will be made as a gray (no matter its hint(s)). Both of those examples are intuitive WYSWYG.

Color as a notion is originated from how human is perceiving one having included its complex processing in ours brains. Instruments which applied to measure color characteristics(densitometers and reflectometers) are based on this human's definition of color. For example there are ''coca-cola red" and "marlboro red" which could be identified by either expert or densitometer. But if you ask a kid what is this color, you get an answer - it's red.

I presume that answer on this challenge newsletter must be simple. Blue (pale blue, hinted blue is not an option), Gray, White, Black, Colorless (isn't it the same black?). I'd deny any references to spectrometers and the like nightvision goggles include :).

I can be wrong, but I think it's Black.

Didn't those who have had the opportunity to look since the question was asked say purple or blue (possibly depending on the time of day at which they looked)?

Fyz

dark white

Friends,

Enjoyed reading the responses. I agree that the shadow is blue or at least tinted towards the blue. Nobody mentioned this reason: water is not perfectly clear, but absorbs more of the red end from the spectrum, so light traveling through water tends to look blue. For this reason, in addition to any comments about the sky being blue, a shadow in snow will appear blue-ish.

--JMM