Lighting Challenge #5: Under The Boardwalk

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Old 06 June 2006   #16
Talking

DER WASSERDRUCK!

I'm all over this one

/Z
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Mr Zap Andersson - Random Rendering Guy at Autodesk Inc.
old mr blog: mentalraytips.com | Stuff: www.Master-Zap.com | Follow me on TWITTER
 
Old 06 June 2006   #17
@ Sherif.Nagib - Welcome! You can still do the fruitbowl or kitchen scene if you want. The order you try things is up to you.

@ polymess - Great start! I already have good feeling about this challenge, it could turn into something as big as the bottle collection.

@ slatr - Thanks. So this is a better LWO file to host than the one I have, because it splits up the objects into separate objects? I guess I can switch which file is there then, thanks...

-jeremy
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Old 06 June 2006   #18
File for Lightwave

Hi Jeremey, it seems Messiah retains more of the original material/surface data. I open the object in Messiah and then save as a LWO. This doesn't really divide the model up, but it does divide it so that diffrent areas such as the fish, water ect.. can have surfaces or material applied seperately. (I think I got that right

See screen for a division listing of surfaces/materials to see if you agree.

Thanks,

Brian

edit closer up view
http://i5.tinypic.com/14o67bc.png

Last edited by slatr : 06 June 2006 at 08:07 PM.
 
Old 06 June 2006   #19
Thanks slatr. There is some fog in this one, but not enough I guess...

Thanks Jeremy.
Yes I have a good feeling about this challenge too. It's such a nice scene to work with.

Had no problem with the Lightwave scene. It's not that big or complicated, so it was easy to give the different objects new materials...

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Old 06 June 2006   #20
Hi, I'm new to this and would like to join, just one quick question. Is there a size limit we want to keep these renders to? Thanks in advance.
 
Old 06 June 2006   #21
Woah...So quickly another challenge is up~!!! kudos

Originally Posted by MT-Cup: Hi, I'm new to this and would like to join, just one quick question. Is there a size limit we want to keep these renders to? Thanks in advance.


Limit??? I guess there's no limit to the size of render. You could have a large image and then resize it to be posted here and then have a link to allow others to access the larger image for details. Hope that answers your question.
 
Old 06 June 2006   #22
hello! i would like to enter these lighting challenges. I recently took a lighting course for maya, and would like to continue defining my techniques!
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Old 06 June 2006   #23
Talking

A quick test.... caustics need more photons....



/Z
__________________
Mr Zap Andersson - Random Rendering Guy at Autodesk Inc.
old mr blog: mentalraytips.com | Stuff: www.Master-Zap.com | Follow me on TWITTER
 
Old 06 June 2006   #24
Nice Start, MZ!

I'm trying to figure out what's going on with the things that push through the water surface, like why does the boat go yellow-gray-yellow? It looks almost as though there's a reflective part of the water surface that suddenly ends at a line starting at the top of the gray part of the boat? (Maybe it's a fresnel effect thing over-responding to a sudden angle change caused by a procedural bump map on the surface?)

-jeremy
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Old 06 June 2006   #25
Talking

Originally Posted by jeremybirn: Nice Start, MZ!

I'm trying to figure out what's going on with the things that push through the water surface, like why does the boat go yellow-gray-yellow? It looks almost as though there's a reflective part of the water surface that suddenly ends at a line starting at the top of the gray part of the boat? (Maybe it's a fresnel effect thing over-responding to a sudden angle change caused by a procedural bump map on the surface?)


Actually, that is completely correct (well, not 100%, I'll get to that). Do you dive? Or have a pool you can take a hop into and check this kind of stuff out?

I did some empirical studies in my pool, and this effect is completley accurate.

When light goes from a higher IOR to a lower (water to air) there is total internal reflection happening. I.e. for the most part, water seen "from below" is perfectly 100% reflective.

This happens because (as you know, but I'm explaining to our listeners here ) when going from a higher IOR to a lower, rays bends "away" from the normal. At a certain angle, the ray coming from under water would actually bend so much "away" from the normal above the water the resulting ray would actually be below the water again! (What happens quantuum-mechanically is that it is at this angle real-world photons can't tunnle through the water/air interface). It is at this point the surface insteads becomes a perfect reflector. This happens very abruptly, but not quite as abruptly as the fresnel() function in most renderers show it. That is what is not "100%" with this effect here; it would be a liiiiiiiiiiiitle bit gradual. Not much, mind you, but not a visible line, as here.

This also means all rays "above" this point are almost bent so they go below the surface - i.e. they "graze" the surface.

So going from low to high:

- So, yes, you see the boat, coz it's under water.

- Then you see the water surface. The angle is "shallow" enough to cause Total Internal Reflection (TIR). So you are seeing the sea floor, not the boat.

- Then, when the angle becomes large enough to "break" the barrier of TIR, we suddenly see "out" of the water. (Anyone who dives knows you can only see "the outside world" in a fairly narrow "window" above your head).
Now, since the rays at the edge of this "hole of visibility" are near-grazing, they will indeed surf the surface very tightly... and hit our boat just above the water line.

So yes, it looks bizarre. Completely bizarre.

But I spent the afternoon in the pool with my kids w. my diving mask verifying it's correctness - it looks bizzare in real life too.

What is not 100%, as I said, is that real water has much more bumpiness and displacement than this (so what you actualy see "up" through the water is much more distorted) AND the fact that the "border" of this effect isn't as "hard" as shown here. I think it's due to the fact that the effect actually happens at different points for different wavelengths that it appears slighlty more "softened" in real life. Still, it is a pretty abrupt effect.

Thanks for the comment, tho

/Z
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Mr Zap Andersson - Random Rendering Guy at Autodesk Inc.
old mr blog: mentalraytips.com | Stuff: www.Master-Zap.com | Follow me on TWITTER

Last edited by MasterZap : 06 June 2006 at 05:49 PM.
 
Old 06 June 2006   #26
Wow, that's interesting, MasterZap! Can we all come to your pool now?

My question is why in your image you have that effect only for the boat and not for the peer.
I like the fog effect in the distance, very convincing.
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Old 06 June 2006   #27
Talking

Originally Posted by silvia: Wow, that's interesting, MasterZap! Can we all come to your pool now?


Party at my place, huh? Well, BYOB in that case

Plus you need to fly to Sweden. (And not be too many (it's a tiny pool)).

Quote: My question is why in your image you have that effect only for the boat and not for the peer.


I do. But you see the "legs" (hmm, whats the proper english term?) of the pier reflected. If they were textured and not just colored, this would be more evident. I.e. going from below to up, as for the boat, you have

1. The "legs" directly visible, since they are underwater

2. The "legs" reflected in the TIR

3. The "legs" as seen through the water above the surface.

They "sorta" join up, out of largely serendipipipipdity (how do you spell that )

Quote: I like the fog effect in the distance, very convincing.


Thanks.

I didn't use parti_volume as I planned, tho, it's a traditional "depth fade" fog.

/Z
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Mr Zap Andersson - Random Rendering Guy at Autodesk Inc.
old mr blog: mentalraytips.com | Stuff: www.Master-Zap.com | Follow me on TWITTER

Last edited by MasterZap : 06 June 2006 at 06:15 PM.
 
Old 06 June 2006   #28
Great start MasterZap.

Looking forward to sea... this finish...
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Old 06 June 2006   #29
Wink

Originally Posted by polymess: Looking forward to sea... this finish...


It's gonna be pun.

*ouch*

/Z
__________________
Mr Zap Andersson - Random Rendering Guy at Autodesk Inc.
old mr blog: mentalraytips.com | Stuff: www.Master-Zap.com | Follow me on TWITTER
 
Old 06 June 2006   #30
Master Zap's wonderful explaination almost tempted me to go swimming today. But here some are reference shots I just cooked up in my kitchen, using a green spatula handle stuck into the carafe of a Mr. Coffee:


Starting at the bottom, you can see the bottom of the spatula handle, then the transition (what an amazing transition! ohhh...) into a reflection of the handle in the water surface, and then we go back into the view of the spatula looking up through the water surface at the dry part of the spatula.

(Edit: For the sake of clarity, the top edge of the water in the container is at the very top of the image. The line near the center of the image is NOT the top of where the liquid is located, even though it looks a bit similar to that.)


Of course this is much smoother, calmer, cleaner water than you'd find in most ponds (at least speaking for the US), but here's a close-up look at how the two "lines" can appear between the areas.

-jeremy
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Jeremy Birn
Author, Digital Lighting & Rendering, 3rd Edition

Last edited by jeremybirn : 06 June 2006 at 07:58 PM.
 
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