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View Full Version : Distant light does not create Parallel shadow ?!



JML
08-19-2005, 11:40 AM
here are 2 animations to show different shadow effects at different FOV

the camera FOV in the first one was 65 degrees,
the second one was 40 degrees


why are the shadows not parallel in both ?
shouldn't it be ?

any comments are welcome as I'm trying to understand what's happening

JML
08-19-2005, 01:26 PM
on the video, at the end, from the top, you can see that the distant light send parallele shadows, but,
when you are at the begining, on the ground, the shadow doesn't appear to be parallele..
why?

Wade
08-19-2005, 03:04 PM
Your shadows are parallele, but just like anything else in this world they will look to be distored by your point of view and the perspective effect.

It is a real world effect.

Try looking straight down you will see that they are parallele. :angel:

JML
08-19-2005, 04:15 PM
I know when you look from the top, they are parallele, (as you see in the animation)
but I don't understand why the shadow is so far from being parallele when you are on the ground..
I wonder if the lens shader effect in lw9 will correct this.. or maybe it's just normal?
on a real photo, all shadows are perfectly parallele..

mkiii
08-19-2005, 04:32 PM
You think a real photo has no perspective?

As for the shadows. If your pixel aspect ratio is something other than 1, and I mean *way* off 1, you will eventually get a distorted infinite light shadow, otherwise it is parallell.

toby
08-19-2005, 07:19 PM
They don't look parallel for the same reason train tracks don't look parallel when you look down their length -

Surrealist.
08-19-2005, 09:10 PM
Well, My 2cents. I think the thing you may be looking at is the difference between the two poles. When playing back the animation the ground plane was at an angle, this most likely means that the camera was angled slightly.

I think If you want to get a more scientific result, make sure that everthing is quared first and then run your test, you might find the distortion more predictable that way.

If you want to get a completely "pure" camera move. Try this:

Set a null at 0,0,0. Parent the camera to it. We'll call it Camera Null

Set another null at 0,0,0. Target the camera to that null. "Target Null"

Now move the camera back. Make sure all of the rotation channels for it are at 0. Then simply turn off all rotation channels except pitch on the Camera Null and rotate it 90 degrees so that the camera is directly above the two evenly spaced poles. The target null will cause it to remain contiually pointed directly at the center of the two poles no matter how you rotate it.

Now run some tests and try the different fields of view and even try shifting the target around to see what effects the camera roatation has on the perspective.

This way you can change predictable portions of the test one by one.

Well, just an idea, if you care to try. :)

JML
08-19-2005, 09:27 PM
here what happened,

a co-worker (one of the one that like to complain about LW because he loves another 3dprogram, sigh :rolleyes: ) showed me a render of a street he was working on, and told me "how come the shadows of the streetlights are not "parallele"?.
then I told him, that if he's using a distant light (he was), all shadows are perfectly parallel. and I showed him a top view that proved that.

but still, another co-worker and his manager said the same thing, "this doesn't happen in photos" blabla, then I started to try stuff around, and there I was confuse. :cursin: did not know whatever it was normal or not..

I never had those kind of shadow issue because I rarely put a sun light behind the camera because I think it make things look flat..

I'm trying to find a photo with the same kind of shadow to show them it's normal.. if it is..
anybody have something like that close by?

thanks

JML
08-19-2005, 09:45 PM
They don't look parallel for the same reason train tracks don't look parallel when you look down their length -

thanks toby !
after thinking a little about it, it's very good example,
and it's because they put their sun lights right behind the camera,
I was easily able to find lots of photos that illustrate that, (with sun behind camera)

do you guys see what I have to deal with at work ? :bangwall: :D

Surrealist.
08-19-2005, 10:50 PM
Morons. I say. Morons! :)

toby
08-19-2005, 11:07 PM
Don't tell me, they're Max peons, right? :twak:

JML
08-20-2005, 11:18 AM
Don't tell me, they're Max peons, right? :twak:
close but no, those ones were maya , the max ones are not as bad.. at least here.

everyday, I hear the maya peons talk about how superiors it is to everything and how lw is crappy... , every day .
it gets really annoying.. :bangwall:

I guess they are really pissed because we have not even one maya licence :D

toby
08-20-2005, 01:56 PM
Well at least Maya works! But using it for anything less than feature films is like entering an auto race with a pickup truck. It can carry more, but it's slow-going.

JML, your website is amazing. Did you do everything in those images? Designs too? Tell me about the b&w version of this (beautiful) image, is it just turned to b&w, or did you adjust values to make it better?

JML
08-20-2005, 02:31 PM
Well at least Maya works! But using it for anything less than feature films is like entering an auto race with a pickup truck. It can carry more, but it's slow-going.
JML, your website is amazing. Did you do everything in those images? Designs too? Tell me about the b&w version of this (beautiful) image, is it just turned to b&w, or did you adjust values to make it better?

thank you Toby, I did everything on those images, those are personal projects for fun, I'm doing mostly architectural stuff at work.

about the room, it's the first interior I did to show where I work we could do
soft lighting without using radiosity and using area lights instead to save time.. it was a few years ago now..
I changed it in photoshop, I made it black and white and adjusted the level, that's pretty much it I think. I like the black and white better, and some people tell me I should remove the color one from the website..

I saw you were working at DigitalDomain, congratulation, must be great!
a few years ago, I remember I e-mailed EricHanson and he was nice to answer and give me advice on one of the picture I was working on.
(I saw some images we worked on for the 5 element and it was excelent)
is he still at digital domain?

toby
08-20-2005, 03:27 PM
I like both, your choice of colors and their layout remind me that I need to sign up for some classes at my local art school. I don't suppose you could post a far-less compressed version of it?

Thanks, DD is very cool, but I work in commercials where you don't learn finer points of imagery - I'd like to move on to features but that requires learning Maya. Good program, but I prefer to enjoy my work. :P

Never heard of Mr. Hanson, but he's probably not in commercials - don't get me wrong, DD constantly does award-winning commercials, it's just not quite the same - but now that I think about it, classes will probably do more for me than features will -

JML
08-20-2005, 09:15 PM
I like both, your choice of colors and their layout remind me that I need to sign up for some classes at my local art school. I don't suppose you could post a far-less compressed version of it?


the picture is actually not too compressed, the 'blocks' pattern on the ceiling comes from one of the area light.. that was my first interior with this setup..
I later learned basic things, like excluding all ground objects from the floor light,etc.. right now one of the area light is passing through the jacouzy, so blocking part of the light, then losing area light quality..then add lots of noise on the ceiling...

I'm updating my website by switching from a 800x600 layout to 1024x768.. so when I will re-render that image, I will make sure the lighting is clean. I will let you know.

toby
08-20-2005, 09:37 PM
No, it's really the jpg artifacts that are bugging me - I didn't even notice the things you mentioned, maybe I would if I saw the uncompressed version, but unlike Arch clients I don't expect or want absolutely smooth lighting/unrealistic perfection... I know how they can be... :screwy:

JML
08-20-2005, 09:42 PM
yes, I did not notice that, that's pretty bad.
I forgot, I already rendered that one last week, I got 5 more to re-render but that one was already done,
so this one should be pretty clean..

enjoy :D

toby
08-20-2005, 09:54 PM
sssooowwweeeeet!