Light bleed

[MaxP]

Next, if I change to an area shadow, the wall to the right doesn't appear to cast a shadow.

[MaxP]

Finally, I find if I bring the light inside the room and add another, I get a huge amount of reflection off the end wall. Is this simply specular reflection and how can I reduce the effect?

(Apologies about the poor lighting and materials)

[thorn3d]

The lights are behaving as they should, so far as i can tell. It looks like the problem is - you aren't experienced enough with using lights.

thorn

[MaxP]

I did not mean to imply that I felt there was a problem in the way Cinema renders the scenes, but in my understanding of what is going on.

While I can guess why the light bleed and reflection (first and third example) occur, I am surprised at the magnitude of the light bleed effect and would like to know how best to overcome it. What I would also be grateful for is an explanation of why the area and soft shadow renders differ so greatly.

Regards,

Max

[flingster]

max what is it you want to achieve in terms of light the room? i'm finding a little difficult to tell what setup you have at moment.
how many lights do you currently have?
what settings on each light...shadow/falloff/brightness.
what are those windows alphas?
dunno a bit more info...or maybe the scene file to have a look at?

sorry can't be of more help bud...hopefully we can help ya out there..

i guess thorn had a grumpy day today...he might be right but surely this is the place to come and get more experience?:shrug:

[JamesMK]

As pointed out by neverwake, the problem is simply that which solves itself with more experience. Lights in 3D do not behave like one would expect, at least not until you get more used to it (then you'll start complaining about real lights doing stuff they shouldn't instead :D )

There's too much stuff concerning this matter than anyone would want to go into probably... BUT, as Flingster replied in here, his mere appearance reminded me of a thread we had going here for a while that applies rather well to what you're trying to do, so I think you can get some good ideas by looking into it and playing around with the various .c4d-files available in it -> http://www.cgtalk.com/showthread.php?s=&threadid=111894&highlight=radiosity

Hope that helps!

[flingster]

Originally posted by JamesMK
As pointed out by neverwake, the problem is simply that which solves itself with more experience. Lights in 3D do not behave like one would expect, at least not until you get more used to it (then you'll start complaining about real lights doing stuff they shouldn't instead :D )

There's too much stuff concerning this matter than anyone would want to go into probably... BUT, as Flingster replied in here, his mere appearance reminded me of a thread we had going here for a while that applies rather well to what you're trying to do, so I think you can get some good ideas by looking into it and playing around with the various .c4d-files available in it -> http://www.cgtalk.com/showthread.php?s=&threadid=111894&highlight=radiosity

Hope that helps!

Oooh yeah cool thread learn't a lot from that one and a couple of others...we should do another challenge again sometime...maybe something like...here is the room file...now light it the best you can or something like that...dunno will have a think.

:wavey:

[MaxP]

Originally posted by flingster
max what is it you want to achieve in terms of light the room? i'm finding a little difficult to tell what setup you have at moment.
how many lights do you currently have?

Hi flingster, I was mainly playing around with a single, omnidirectional light illuminating a polygonal mesh of a room I had modelled (just experimenting really). At one point, I placed the light outside the walls of the room mesh and noticed some light bleed at the seams of the model and wondered what the best method of preventing the bleed would be.

Later, I changed the shadow type of the omni light from soft to area and while the bleed disappeared, the lighting changed to something where it was almost as if the walls were no longer present on the right hand side of the image (i.e. there is no discernable shadow from the walls), which was a bit unexpected!

Finally, when I brought the light back into the room and added another along the room's axis the wall at the end appeared very washed out and I wasn't sure what the best way of changing the materials or light settings to control the reflection would be. Hence the questions.

what settings on each light...shadow/falloff/brightness.
what are those windows alphas?

The lights are basic omnidirectional lights, at 100% brightness but with different shadow types applied. The windows are made up of polygons with a basic glass material applied.

Ah, I've just noticed the lights have no falloff, which helps to explain why there's so much reflection off the end wall.

dunno a bit more info...or maybe the scene file to have a look at?

It's pretty big and I was only playing around, trying to learn really so it would probably be overkill. I think it's plain that I need to do a bit more playing with lights ... thanks for the offer though.
sorry can't be of more help bud...hopefully we can help ya out there..

Thanks, the threads people have suggested have been useful. The Sigraph course notes look great.

i guess thorn had a grumpy day today...he might be right but surely this is the place to come and get more experience?:shrug:

I hope so! I've always thought CGTalk an excellent resource. I do need to play around with lights a bit more though ....

[Per-Anders]

post number 1 : look at your shadow bias, this controls the distance that the shadow starts away from the object casting the shadow, this is because soft shadows are bitmaps, and you need to make sure they dont' start before the object begins, although sometimes you might want to abuse this effect for some semi ambient occlusion style effects. also of course check your shadow resolution.

post number 2 : the size of the area shadow is probably far too large. this is the virtual area of the lightsource, this is just making your shadows far too diffuse to be clear.

post number 3 : omni lights send out light in all directions, and add together, it looks like you have two omnis at the end of your hallway, you also don't appear to have any falloff going on there, this means that the end walls are getting the accumulated light of all the lights in that room.

lighting is just something you learn with experience. you will just have to experiment till you understand what's going on.

[flingster]

don't forget...default 100...can be 40% or 120%...heh heh just to confuse ya...when did ya ever see a default room? nope...

what i sometimes do is take lights in there singularity first:
eg falloff and shadow...and change it to an unusual colour eg blue or red...whatever...
then turn on and off...and render...
then next light do the same...but with a different colour...
then turn both lights on at same time and see colours/shadow etc...how they are affecting each other is then easier to see.
loads of exercises you could do...eg try lighting with just one spot for example...and one omni...then try lighting with 3/5 lights...very often its hard to tell what impact each light is having on your scene...need to break down and then kinda build up...now i don't know if this is what youre supposed to do or not...but it does help you get a whole concept of what is actually happening..
things also baring in mind are render times on shadows...eg area shadows are higher....you can have negative brightness...and contrast can help sometimes...falloff is your friend...but it is a bit of a science to say the least...just experiment and experiment...but understand what the settings are actually doing..v important. last make sure you have a clear picture of what you want to achieve and how you would expect a room to be lit real world...hope this helps a little.

take that room you got...light it loads of different ways...then post em...and let us know how you get on...good luck...

[kromekat]

then turn on and off...and render...
then next light do the same...but with a different colour...


Flingster - I have used that method to work out lighting problems myself - it really helps to see exactly where lights are falling and whether they are being effective or not in more complex environments.:beer:

[MaxP]

Thanks for all the great feedback everyone. As well as the falloff problem, I've discovered another cause of the effects that I didn't understand in my original scene. As mdme_sadie suggests the scale of the object being lit is much smaller than the area illuminated by the light(s).

I'll play around some more using the techniques suggested by flingster and when I've got something I like I'll post the results.

[MaxP]

Right - I've reread the manual, followed up the links to lighting tutorials, played around for hours and this is the result. Still looks a bit too clean, and outside is very much unfinished, but I think it looks quite nice. No radiosity by the way ....

For those that can access renderosity there's a hi res image at :

http://www.renderosity.com/viewed.ez?galleryid=606436&Start=1&Artist=Dr+Max&ByArtist=Yes

I've also attached a small heavily compressed image to this post.

Thanks for all the lighting pointers ...

Max

[flingster]

well i'd say thats an improvement...some of the pre vis/architect guys maybe able to help ya tweak it...help removing that cg look you mention.
:thumbsup:

[STRAT]

looks much better. wont get much more realistic than that without radiosity unless ur a scanline guru.

try it with radiosity see what happens. you'll opbviously need to switch off or turn down some infill lights you got going there, and another tip - switch off the area lights/shadows. not needed here i think, also will speed up rendering massivly.

[MaxP]

Originally posted by STRAT
looks much better. wont get much more realistic than that without radiosity unless ur a scanline guru.

try it with radiosity see what happens. you'll opbviously need to switch off or turn down some infill lights you got going there, and another tip - switch off the area lights/shadows. not needed here i think, also will speed up rendering massivly.

Thanks for the comments - I'll have a go at doing a radiosity render. In the mean time I've succeeded in uploading the image to my website.

http://www.drmax.f2s.com/Gallery.jpg

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