[stylus]

I've come to a realization: I don't know what colour shadows are. Looking at the shadows around me is getting me all frazzled because I'm looking at a shadow and after 5 minutes, I finally conclude that I have no clue what colour(s) is in it. And because I don't know how shadows work in real life, I can't effectively use it in art. So I've scoured the net, searched the forums, and have been chastised a bit for not knowing, but I still don't know what colour shadows are supposed to be. So, generally, what colour are shadows?

This tutorial says that shadows are generally less saturated than an object's lit areas (presumably of the colour of the object?). But this artist says that shadows are more saturated than the lit areas and are basically more saturated versions of the ambient light. Looking around myself, I think this makes more sense. So if I were to make a formula of a shadow's colour (cuz, y'know, math is cool ), would it be inaccurate to have something like:

Colour of a shadow = Colour of the object + More saturated version of the ambient light

Sorry if I'm not using the exact terminology of some of these things. I believe I understand how light works, but I can't connect what I know to determine what colour shadows are.

[yesso]

The R, G or B light reflected by a surface is proportional to the amount of R, G or B of light hitting it. However, what a lot of people don't realize is that any object that reflects light to your eyes, so that you can see a non-black color, also reflects light onto other objects, and acts just as if it were itself a light source.

In fact, the way some advanced 3D renderers work is by rendering the whole scene from the perspective of a point on a surface, in order to figure out what illumination reaches that point on the surface. So, if a light source is visible from that point, it has a big effect on the color—if the light source is occluded, it has no effect, but the point on the surface still "sees" other things in the room, so it is illuminated by that. Note that if the light source is not infinitely small, there will be many parts of the surface that see only part of the light, so you get a penumbra.

So, the simple answer is that the color of shadows is more biased toward the color of the other objects in the room, (or at least the color they appear,) than the color of the light source itself.

If something is illuminated outside, on a sunny day when the sun is going down, you will notice surfaces are slightly yellowish (color of the sun) when pointed toward the sun, and somewhat bluish (color of the sky) when pointed to the non-sun portion of the sky. You can usually tell whether it's cloudy just by looking at objects on the ground, because everything will be uniform gray.

As for why they would appear more or less saturated, remember that cameras receive light according to an exposure function. This is applied separately for R, G and B. So, even though two points on a surface may be the exact same color in real life, a camera will respond less to a color channel as it becomes brighter, causing the overall color to become less saturated.

Use color picker in photoshop or a similar app on some photos to compare the RGB values to see how they behave.

[Lunatique]

You need to think about what exactly is lighting the shadows. Shadows aren't always completely black--it's just receiving less light than the lit side of objects. When light bounces around in an environment, it bounced onto the unlit side of objects too, but since it's bounced instead of direct, the brightness is not as strong, therefore even though it's lighting the unlit side of objects, when compared to the lit side is a lot darker.

Now think about this--the unlit side of objects can also receive light from secondary light sources that aren't simply from bounced direct light. For example, a person sitting in a room, facing a window, and a red light is shining on his back. The sun outside is very bright so his back is unlit, but receiving some of the bounced light from the sun light entering the room and bouncing off the walls, ceiling, floor...etc. If you don't turn on the red light, then the the "color" of the shadow (unlit side) is simply the same as the lit side, although darker (we're not dealing with saturation issues here yet). This is assuming the walls and items in the room are all neutral in color so the bounced light does not take on any color shift (for example if the a large green desk is right behind the person then the green of the desk will get bounced onto the person's back). Now, if you turn on the red light (let's say a typical 60~100 watt bulb, but red), the "color" of the person's shadow is now a deep red color, because it's receiving majority of its illumination from that red light.

Now, let's say it's night time and outside the window is a big neon sign--the color of yellow. So now, the front of the person is lit with yellow, and the yellow also bounces around in the room and some of the unlit side also has a bit of the yellow as well. If the red light is turned on, then, the back of the person will now be more of an orange color because the bounced yellow is mixed with the red (this is assuming the power of the yelloe neon light is strong enough so that when it is bounced, it's still roughly the intensity as the red light bulb, thus lighting the back of the person in equal ratios--50% yellow, 50% red).

So, to conclude, the "color" of the shadow is all about the color/intensity of the light sources, the colors of the various objects/surrounding surfaces...etc.

This is actually still a bit of a generalization even though it seems I've typed a lot. Color/lighting is not a subject you can talk about in such a short time--it can be quite involved. But I hope this answers some of your questions.

[Mikko K]

I'd also suggest playing with some 3d app and rendering some simple scenes. That would help you understand core shadow vs. cast shadow, occlusion etc..

[Nag]

It�s hard to put rules around things and there are always exceptions. The only one that seems to apply all the time (well most of the time like 98%) is that if the light is warm then the shadows are cooler than the light and if the light is cool then the shadows are warmer then the light. This works for me at least.

[watmough]

Nag hit it right on the head.

[Lunatique]

Isn't that too generalized?

[retro]

let me rephrase this to get it right:

the shadows are warmer or cooler than the light and the light is warmer or cooler than the shadows (???)

on the other hand i have to admit the 98 percent

[stylus]

Hey, thanks for the responses, everyone! I'm just dropping a quick note to say I'm going to read through everything when I get the chance(unfortunately have my head between school and a hard place right now).

Mikkko K: Yeah, I was trained in 3ds during a practicum with an architectural firm. They taught me what ambient and bounced light were and how they worked. But I never could connect them or see how they affected shadows. I followed the tutorials starting here (I think there are 12 or so), so if they explain how shadows work and I missed it, let me know: http://www.cgarchitect.com/resources/tutorials/smoke3d/tutorial1.asp

Thanks for the 98% rule. I at least know that one, and now I know it's reliable. What's an example that could be part of the other 2%?

And double thanks to everyone for being very hospitable. I've asked this question on another art forum and was met with some blunt and unncessary comments. I appreciate that you all respect my trying to learn by example from other people.

[Mikko K]

Stylus> Maybe you could post some artwork of yours if you want more useful advice. Your question is a very broad one, and can light and shadows really be separated? I think they're both part of the same thing - a way to show form in a scene.

One thing that I noticed is that they speak of "ambient light" in that tutorial.
There really isn't such a thing in the real world, and I wouldn't use it in my renderings either.

Using ambient light is basically a quick way of upping the brightness/gamma of a scene without using real lights. I'd rather use more low intensity lights in the scene (points or spots indoors) and maybe several directional lights for the outdoor scenes (one for the sun, one for the blue bounce light). Then ideally you would use radiosity to get realistic light bounces.

I don't know if you knew all this already, but it's difficult to tell exactly where you're at without seeing your work.

[Lunatique]

For me, at some point I stopped thinking about the warm/cool rule and simply thought about the color(s) of my light source(s), and the colors of surrounding surfaces. That is a much more logical way of thinking about lighting and colors to me.

[Erling]

I agree with Lunatique, if you are really serious about understanding painting, you have to move beyond the rule-of-thumbs pretty early on. Even they can be useful simplifications when starting out. I feel they confused me to begin with, and thinking back I'm shocked how many art teachers I had that didn't explain exactly how it really works and only just gave out these thumb rules. For example I was told warm light - cool shadow and the other way around. Which is an over simplifycation and confused me (and led me to some awful warm tone paintings with oversaturated blue shadows) Warm light - coolER shadow is a more useful rule of thumb, but still not accurate in all cases. If a moderately warm light bounces back off a hot red orange background, the shadow could have warmer albeit darker tones. I also remember other rules, like formulas for mixing shadow color with local color +complimentary color. Sounds almost like woodoo and relying on blind faith.

The right way is simply to understand and see the light sources. If there is no light there is just absolute black, think of pictures of asteroids in space with only one light source (the sun) and no reflected light.
On a clear sunny day there might be 2 main light sources, the direct sunlight and the luminescent blue of the sky. In this case the shadows have a blue cast because of the sky illuminating whatever is not drowned in sunlight. Then if we add reflected light, for example a football player in a white uniform on a clear sunny day standing on green grass. We would have the same two lightsources as before, plus green light from the grass that is a result of the sunlight hitting the grass around the player and bouncing back. The shadows would then have a blue green hue especially on surfaces that face the green grass and closest to it.
I hope this helps

[Nag]

[Erling]

Yes, sorry if it came across I was correcting you, I was just saying, back in the day some of my teachers oversimplified even this simple rule.

[retro]

---

[Erling]

Yes it is confusing and really the only real meaning in that "rule" is that shadows are a different temperature than the light. It is really just telling us to pay attention to relative color temperatures. In the example I had above where a moderately warm light bounced back of a really warm background the you can say the "rule" would still hold true because the light would appear cool compared to the warm reflected light, and therefore cool light warm shadow. QED.
Is anybody else getting a headache?

[Destinatus]

This article might "shed a little light on the subject." I found it immensely helpful a few years ago.

http://www.itchy-animation.co.uk/light.htm

[yesso]

Maybe I'm being pretentious here, since I'm not an artist, but I think part of what's important is to learn to use your intuition.

It seems that one of two things can be the case: either you can look at your shadows and think that they look wrong, in which case you can begin the process of searching heuristically for what looks right. Or, when you look at it, you can't tell that it's wrong, it just looks right to you. In this case, it doesn't matter if it's actually wrong mathematically or scientifically, since humans looking at it will find that it looks good.

If it doesn't look right to you, then don't do it, even if the "rules" dictate that it's right.

For example, if you actually add green to a football player because he is standing on grass, you will probably find that it looks wrong, unless you really put only a very fine (hardly perceptible) amount of green. It turns out that the luminosity of the sky is orders of magnitude higher than the grass, even though (because of the exposure function) we see it as only a few times brighter. So the grass doesn't have much of an effect relative to the sky. Your intuition can tell you that, even if you didn't do the actual luminosity calculations.

[yesso]

Wow, that link is really awesome. While I was reading it I was thinking "This guy should publish a book". Then it turns out he is turning it into a book.

[Nag]

Great link Destinatus, I remember coming across it some time ago and I forgot to bookmark it "click"

No worries Erling, was�nt sure who you were reffering to. Great to see other people from the island of frozen rock here, had�nt noticed you before. =)

[Erling]

Thanks for posting the link... well explained.

Nag, same to you, I'm a master lurker - og �fram �sland

[genocell]

I am much a master lurker myself. Thank you very much for the link. It helps me a lot in understanding this aspect of lighting. Also thank you for everyone who contributed their posts.

Though it ended abruptly in page 5 I'm looking forward for the book that he mentioned in that page.