advice needed on radiosity lighting...

[gScott]

as a lot of my work involves indoor/outdoor space i'm practising using 'sunlight' coming in through large glazed doors. i'm getting strange effects from the custom radiosity renderer where windows + glass objects are taking the "glow" from the floor <i think>. it looks like a fine layer of dust over all the glass + i can't get it "clear" with light reflections.

final renderworks gives a dark clear glass <too dark>

fast radiosity gives reasonable colour but bad lighting

final radiosity gives good colour but weird lines all over the flat rectangular ceiling...

my questions:

1 - what lux value should the "sun" have? real values would be 400 morning/afternoon up to 1000 mid-day. i'm using 5000 kelvin as temperature which is "standard daylight"

VW12 gives 75%, white.

2 - should i be using the "auto-adjust exposure" or should i manually adjust lights to get a balanced effect? could the "auto-adjust exposure" be causing the "dusting" on the glass?

3 - what are reasonable radiosity figures?

for this one room render i'm using <top to bottom> 1.9m, 1.6m, 800mm, 85%, 90%, create ambient=on

i'm really enjoying learning the ropes but am getting a bit frustrated at the apparent randomness between the effects of final + custom radiosity. i have taken dan's tips on white ceilings, seen at http://www.danjansenson.com/whiteceiling/

any advice would be gratefully received

<if i can figure how to post images i will>

regards

gideon scott

[propstuff]

There's a lot to work through here.

try this thread for a start.

http://techboard.nemetschek.net/ubbthrea...=true#Post46877

cheers

[gScott]

think i've figured how to post images:

you can see the

[gScott]

sorry managed to bugger that up...

you can see the objects at the back appear translucent when they are supposed to be clear glass, and the windows have a slight warm dust/glow. this is as "clear" as i can get it..

regards

gideon

[gScott]

thanks, nicholas,

i fear from that thread that RW is flakier than i suspected...

am i wrong?

or is it a feature designed that way to get our creative juices flowing? particularly at 4am when you've got an early appointment + the thing is rendering weird...

i've spent too many nights doing that with microstation + was hoping that RW would be different...

mmm...

[propstuff]

I'm not sure that flaky is necessarily the right word. It does seem to produce some strange geometric artifacts (if for instance the ceiling intersects the walls), but I think it's more a matter of being tricky to set up rather than flakey.

I was hoping for something along the lines of setting up a sun with Global Illumination, and just getting a result that looked something like what you would see in reality, but it seems that we still need to add area and fill lights, and resort to tricks like Karre's to make white walls "look white" etc etc.

I was probably dreaming, but again I don't think that means it's flakey as such.

I haven't had any time to work on this recently so if you find some setting "recipies" that work for you, let us know.

N.

[gScott]

nicholas,

i mean flaky in the sense that it does not produce consistent or predictable results...

however, i am collecting all the lighting + surfacing tricks i can, that i hope will make setting up new jobs easier + will post them once i think they do a reasonable job in default circumstances.

i agree that a sun set-up like microstation or sketchup would be extremely useful

[Dave Donley]

my questions:

1 - what lux value should the "sun" have? real values would be 400 morning/afternoon up to 1000 mid-day. i'm using 5000 kelvin as temperature which is "standard daylight"

VW12 gives 75%, white.

2 - should i be using the "auto-adjust exposure" or should i manually adjust lights to get a balanced effect? could the "auto-adjust exposure" be causing the "dusting" on the glass?

3 - what are reasonable radiosity figures?

for this one room render i'm using <top to bottom> 1.9m, 1.6m, 800mm, 85%, 90%, create ambient=on

Hi gideon_scott:

Just guessing without having your file, I think the glass problem could be:

a) Mirror factor on glass set high, try 50% instead

b) Using Glass, Simple instead of Glass, Accurate. That is why I think the yellow frosted thing might be happening.

c) Ambient or Diffuse for the glass being high, I like it at 50%.

d) Using Glass, Accurate and Plain Transparency in the same texture - this is bad as they interfere with each other.

e) Using the Create Ambient radiosity option, usually this results in everything having an ambient color cast until a certain amount of energy has been dealt with. Different models will have a different setting where this color cast will subside.

For a good glass, try using Glass, Accurate by itself (no other Transparency shader set), with Ambient, Diffuse, and Mirror set to 50%. You can also try turning Roughness down to near 0%. Set the texture's Radiosity Options to override and not emit or receive.

1 - The sun and sky produce tens of thousands of lux (the sun up to 100K lux). Usng these values requires using the auto exposure feature. Once you're using the auto exposure feature, lighting is more of balancing cool and warm amounts - the light coming in from area lights located with the window glazing would be cool and soft and the sun would be more of a warm and hard light. With auto exposure levelling out the absolute brightnesses you then are dealing with relative amounts - like 2:1 blue to yellow or 1:1 cool to warm, etc. For sun and sky I find it easier to not use color temperature but instead set them to very pale yellow-orange and very pale blue-ish. Color temperature works well for electric fixtures though (assuming the color temperature white balance in the layer/viewport lighting options dialog is set to a reasonable average value).

2 - I recommend using auto exposure with radiosity renderings. The main reason is that indirect lighting effects can be very dim, and without auto exposure on they can be almost missing from the image. Also, it allows you to set the light intensities to real-world numbers initially, then tweak the amounts in a relative way to get the look you are after. Auto exposure can run into problems if the scene is supposed to be dark or contrasty, because it assumes it is supposed to bring the overall brightness up to a well-lit level. The result with some scenes with auto exposure can be an overly-bright, pastel kind of look. In that case I would work without auto exposure.

3 - I think you could increase the Inclusion value here; I am wondering if the black door frames are caused by them being excluded. The small detail could get smaller, if you have the time. I would uncheck the create ambient option, and turn off all ambient in the layer lighting options dialog.

The ceiling looks weird because it is set to constant reflectivity and so it doesn't respond to the rest of the scene's lighting. Also, setting it to Constant is keeping any light from bouncing off of the ceiling onto the rest of the room (setting it to Constant reflectivity is like setting the texture to not emit and not receive). I would change it to Matte. Don't give the walls anything but Matte (or None) for their reflectivity, because area lights will render very slow with a reflective texture.

HTH,

[Dave Donley]

Re: Flaky results with walls and ceilings:

1. Walls and ceiling and floors must meet up exactly at a shared edge, or you will see "light leaks" and "shadow leaks" because triangles are half-in and half-out of the room. For interiors that means that your floors and ceilings should follow the inside perimeter of your walls. If the floor or ceiling overhangs the walls you will see light and shadow leaks.

2. The other random dark triangle problem in propstuff's previous model was a bug with solid subtractions with radiosity - if you make your ceiling or floors from subtractions or additions you may see this problem. I have also seen this problem with an extrude along path object. This bug will be fixed in the next major release.

[gScott]

dave,

thanks for the comprehensive reply. i'm going to work my way through your points to see how i can improve the renders.

the black frames are deliberate, though...

one thing that struck me, looking at the perspective, is that the floating bulkhead over the doorway doesn't appear to taper away in the perspective <it is an ordinary solid subtraction of 2 extrudes>. it looks fine in wireline or hiddenline, but any other render loses the taper. weird?

thanks again

[Dave Donley]

Hi again gideon_scott:

I'd like to try rendering this model, if you could email me a copy that would be fun (I actually like doing radiosity renderings!)

[gScott]

dave

sorry for not replying to your last mail, i have been snowed under with work + getting to know 12.5....

but have tried a couple of renders on new models + was horrified by the extremely slow render times!!! i noticed that this was due to the default recursion level setting being set WAY up at "64" + the "intial" sizes being VERY small at 30mm!. having cranked these back to my previous settings things are fine, + probably faster than 12.01...

i found that my previous problems with the 'dusty' glass light was directly linked to "create ambient from remaining energy" + accuracy/energy levels below "85". having sorted those out + using some of your setting suggestions i am much happier with the radiosity rendering!

NOW, could you give us some guidance on HDRI, please? the NNA backgrounds give a black background with speckled shadowing, i have downloaded other HDRI files that have visible background images in them that also seem a bit weird... would it be possible to see some rendered examples using this background, so we can get some idea of what to expect?

thanks

[quigley]

Couple of things:

1. If you see light gaps at joints of walls and floors a quick trick is to put something behind it (out of sight) to act as a screen.

2. HDRI is the way to go for external scenes, no question, and for some internals where there is a lot of incoming light. In RW you can use the HDRI as a light source or as a background. Unless the HDRI is a high resolution one though, and appropriate to the scene, use it as a lightsource only and set the background you need.

For your scene, try HDRI for the external lighting and use an area light to highlight parts inside. Also, the milkiness in the windows is due to the reflection of the inside wall on the window. As Dave says know the reflection right down to avoid this.

For more info on HDRI look here:

http://www.lightworks-user.com/hdri.htm

Edited September 25, 2006 by quigley