[nori]

When an object is in shadow, what causes variation in it's value other than local value and reflective light?

[balistic]

Transluscency/sub-surface scattering can come into play. Also, anything that a surface can "see" will have some affect on its value and hue . . . if an object is in a shadow cast by a key light, then that object is going to be getting its illumination from photons reflected from areas of its environment that aren't in shadow.

I tend to think less about light and shadow, and more in terms of what a particular surface can see.

That's how some 3D programs calculate global illumination . . . they just render the whole scene from the vantage point of each polygon, and apply the averaged result as illumination for that polygon.

EDIT: One thing I forgot to mention, and that painters like Mullins and Sargent use to a significant degree, is the contribution of atmospheric perspective. Always remember that we exist not in a void, but in a volume, and that said volume can be illuminated and change the value of solid objects behind it.

A lot of Craig's work involves silhouettes that are lightened by an intervening atmosphere.

[ December 19, 2001: Message edited by: balistic ]

[nori]

that really helped me to think of it that way. What the surface can see.

"silhouettes that are lightened by an intervening atmosphere."

Hmm I'm not quite clear on this example. could you post an image for an example?

[LoTekK]

i don't have my intuos handy at the moment (it's upstairs at my other computer), but basically think of it this way:

for an exaggerated example, think about what you would see if you were standing in an orchard in thick fog... a tree right in front of you would be pretty sharp and its color would be as you would expect it... look a little further, though, and the trees start getting fuzzier and the colors start losing saturation...

now, this happens in clear weather as well, though not as obvious... you would mainly notice this effect with objects in the distance (a series of mountain ranges might go from deep blue-grey to a pale, fuzzy light blue-grey... or something...

hope that helps somewhat...

[balistic]

Here's one by Mullins:
http://www.goodbrush.com/hirez_pgs/forum/forum6/sedone_irish_knight.JPG

Note that there's not much lighting defined . . . the value differences are coming from the atmosphere.

My "Fisher" image also does a bit of that, in the forest areas:
http://www.bprince.com/Fisher1000.jpg