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propstuff

Radiosity problem examples (long post)

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I?ve been trying out the Radiosity in VW12, and there seems to be a problem with the lighting impementation. Firstly, let me say that I?m coming from a position of complete ignorance here. ;-D

Using Radiosity is nothing like Final Quality rendering, and I?m still learning how to control it, so if anyone can point out where I?ve gone wrong; please let me know.

The problem is shown here:

Having ?bright sunlight? shining directly into a room does not brightly light the room. Instead, its murky and hazy and almost dark in the corners, and, at the same time, the chairs near the viewer are washed out and ?overexposed?.

Here?s an example:

-

In reality, direct sun into a room that size, with windows that big, and white walls, would result in a brightly lit room, with everything in clear contrast and definition.

Here are the parameters:

TEXTURE: ceiling and floors:

Pure white, Relectivity; Plastic, Diffuse 100%

(I also tried Phong and no reflectivity, and with different levels of Diffuse, but nothing made it better, only worse)

Walls; Internal, as above, External, over ridden to neither accept or emit.

LIGHT:

1 Sun object; perpendicular to the window on the far right. In this example set to 10,000% brightnesss.

GEOMETRY:

No Ground plane

Floor and ceiling extend only to the Visible walls.

RADIOSITY:

Rendering; defaults, with various recursion levels (no apparent difference)

Object, detail etc; As Shown.

Optimisations; Static view, Visible Surfaces only, Bounds-derive from static view, Allow overrides.

I think that?s all.

In the tests I?ve allowed the solution to go to 100% ( less makes the problem worse)

I?ve tried:

changing the Object, Inclusion sizes etc: (smaller is slightly better, but not significantly- just much slower)

Increasing the brightness of the light: washes-out more the already overexposed near objects, but does not make the room any ?brighter?; just a whiter haze.

Reducing the light brings the furniture into correct contrast, but the room is almost impenetrably dark.

etc etc.?.

Now here?s the same set-up, but with the floor having a ?wood brown? colour, and with the lighting turned down to expose the furniture a bit better.

-

As you can see, the pure white walls and ceiling are still hazy and murky but now a gurky brown.

Again, in reality, the amount of colour imparted to the walls and ceiling by the floor would not be anything like that.

The distribution of the light looks more or less right to me, but it seems that the amount and colour of reflected light is not accurately representing "reality".

I?ve tried changing nearly everything I can think of; so: what?s next?

N.

[ 12-11-2005, 07:43 PM: Message edited by: propstuff ]

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Hi Nicholas, I don't have version 12 yet. But this doesn't look good :-( . Maybe a workaround would be to turn the windows into an area light? I use this workaround with other 3d programs sometimes to reduce rendertime. I can't wait for Version 12 to come to the Netherlands. I hope within a couple of weeks so I can experiment during the Christmas weeks :-)

Good luck and I'm sorry I couldn't be of direct help.

BTW. How are exterior models lit?

Regards,

Peter

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FYI> search posts for link to excellent Povray Tutorial which discusses the fundamentals of raytracing / radiosity algorithms & techniques.

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Hello Propstuff:

What is the Layer Ambient set to (it's now Layer Lighting Options)? Try turning ambient off. Ambient light usually overpowers the radiosity effects and hurts contrast. Try rendering with ambient off, and if the dark parts are too black-looking try 1-10% ambient at most. If you need less than 1% ambient you can make the ambient color darker.

>

Walls; Internal, as above, External, over ridden to neither accept or emit.

<

Excellent, sounds like you've read the supplement. The exterior using up most of your x% energy would be another reason why indirect lighting wouldn't appear in the room.

In this scene you should be able to set the Visible Surfaces Only checkbox in the Optimizations dialog, which will help focus effort in the room versus outside.

>

Floor and ceiling extend only to the Visible walls.

<

This is good.

>

Optimisations; Static view, Visible Surfaces only, Bounds-derive from static view, Allow overrides.

<

Oh, you already has the visible surface only checkbox on, good.

>

I think that?s all.

In the tests I?ve allowed the solution to go to 100% ( less makes the problem worse)

<

Is the Create Ambient from Remaining Energy checkbox on?

HTH,

[ 12-12-2005, 09:41 AM: Message edited by: Dave Donley ]

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Hello again Propstuff:

It may be helpful to use lux instead of % values for the light sources in radiosity modes. For example, try checking Use Emitter in the OI palette Shape pane for your lights, and set them to 3000 lux for both the window area lights and the sun directional light. If this file began in 11.5 you may need to change the directional to lux then footcandles then back to lux to get real lux values out of it (this is not necessary for lights that were created in 12).

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Hi again,

Ray,

turning off Auto Exposure made a big improvement. I wonder what circumstances would be better off with it?

Here's the result with the lght set at 300% instead of 10,000s

-

Much better definition: thankyou Ray.

EJ,

I've looked at POVRay, but rendering by typing code is not something I'm keen on ;-) The tutorials I've seen refer to POVRay controls and attributes and as far as I can see, are not readily relevant to controlling RW

Dave,

I'm sure I had Ambient turned off, but when I went back to look it was on. huh?

I have tried it with Create Ambient from Remaining on and off. Even though Radiosity is set to 100%, turning it on adds extra light to the scene. Is that supposed to happen?

I tried it with Emitter lights previously without success, but no conclusions yet.

Now, returning to problems;

In this one you can see the excessive colour casts from a coloured texture on the floor are still there. Worse possibly. Everthing else is the same as the render above, except the texture colour is an image.

The walls are still taking far too much colour from the walls than would be seen in reality.

You can also see a bug thats happened a couple of times: There are strange angular blocks in the render. There are no geometry changes, just changes to the radiosity settings. -

As well as these strange blocks, sometimes the radiosity renderer seems to loose touch with its Solution. It usually happens after changing a light level or a texture parameter. Following renders will be almost black and the radiosity solution will not proceed past 0%. The only way to fix it is to close the file and re-open it. After that it will recalculate properly.

You can also see in these renders, the strips of light coming through the walls either side of the windows because the windows have not cut into the walls properly.

The excessive colour casts from the floor texture seems to be the major problem at the moment.

N.

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Nich... ignore the Povray command line stuff ( although it's fundamental to understanding the technology ) ... who needs it thanks to NNA... I was referring instead to the description of the mathematical foundations of Raytracing which describe the interactions between objects & light rays and the boolean calculations required to determine intersections. As I recall, the tutorial also provides tips & tricks for minimizing the processor rendering cycles especially at object intersections.

By the way the rendering issues presented are very instructive and help to ease the way forward for the rest of us lagards : )

Hopefully, the issues you've uncovered will be resolved to everyones satisfaction.

Those light penetrations at the wall intersections are freaky ...

have you tried this trick yet > add a compensatory directional light source behind the camera view ... this would allow for reflections on the inside of the glass, hilight the wall & furniture coloring, mute the floor reflections and via interference ... prevent the exterior light from dominating the scene?

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Hello again propstuff:

Auto exposure serves two purposes. One is when you use emitters that have real-world light values (well over 100%), it brings the brightnesses down to the 0..255 range that can be displayed on a computer. The other is that it brightens up dark effects that would not be visible if you had a straight ramp from 0 to the brightest values. If you are not using emitters then you can get by without auto exposure on and by controlling over-bright regions by tweaking light brightnesses. We are actively improving this feature in several ways for 12.0.1.

I wouldn't expect the created ambient to have a visible effect if the solution went to 100%. Anything less than 100% would result in a "color cast" and additional brightness, and also less contrast.

The advantage of using emitters here is that you could set both lights to use lux. The window area lights will automatically produce light proportional to their area using lux. Also, you can then straightforwardly control the proportion of "window" or "sky" light versus sunlight. I think to reduce the effect of the orange glow from the floor you could pump out more light from the windows, versus the sun. Not using lux makes this trickier if your windows are different sizes.

If you have auto exposure turned off you will have to use low lux values (hundreds versus thousands) so that the scene doesn't quickly become overexposed.

The big black triangle on the ceiling is weird. Do multiple copies of the ceiling overlap there? I have also seen speckly artifacts when 3D polygons with no surface area are in the scene, but this is not speckly.

If you could compress and email this file to me I might be able to find out what is going wrong there.

The gaps in the walls are also strange and something I haven't seen before. The file would help to find this out too.

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Dave,

I've just sent you the file.

A couple of points:

There are no area lights in the scene. I made some (they are on the "Hide" layer) but not active. There are also some interior lights not active.

I haven't tried having area lights and the Sun; would the sun shine through the area light? I think the colour casts are unfortunate; I was hoping that simply putting in a Sun would acurately reproduce what you would see in the real world. I tried turning down the Diffuse on the floor texture to reduce it but the colour remained and it just got darker in there. :-(

The triangle things are not due to any geometry; they are random bugginess, like the Radiosity getting stuck at 0%, after changing lighting or texture parameters. Closing the file makes them go away.

The ambient-remaining-after-100%-radiosity thing makes a difference in lighting about equivalent to going from 300% light object to 400%.

got to go now,

Thanks Dave, let us know....

Oh, BTW, with the gaps next to the windows: you can also see that the splay on the wall part of the window does not match into the rest of the wall and there is a distinct texture difference between the 2 parts. Perhaps there's something in the (many new)window settings I should change?

cheers,

N.

[ 12-13-2005, 04:32 PM: Message edited by: propstuff ]

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Hello again propstuff:

A lot of stuff going on here. Here are the things I see in this file.

I haven't yet seen the black triangle bug when rendering this file. Did this only happen after the 0% problem?

We have a bug report already about the solution not resuming after pressing ESC or after the time limit has stopped the solution. This is within the Custom Radiosity Options dialog. The workaround is to leave the dialog and then bring it up again. Did the 0% problem start happening after canceling the radiosity process?

I am seeing the window trim not casting shadows as in your rendering. I have filed a bug on this. I can get the shadows to be correct if I turn off the exterior trim for each window. It may have something to do with the wall splay and the trim together.

The windows extend beyond the wall top and bottom. At first I thought this might be the reason for the shadow problem but changing them to fit inside the wall didn't fix it.

There are "shadow leaks" shown where the ceiling meets the walls especially in the top right corner. One reason is that the ceiling edges don't exactly match the wall edges. I would redraw this as a 3D polygon with the vertices snapped exactly to the (inside edge) wall vertices. The reason I would use a 3D polygon (or a floor if you don't need the texture on the ceiling) is because the triangular edges visible on the ceiling happen because the ceiling is a textured solid section and the facets from these are not merged together like other objects (yet).

Area lights are slower with reflective shaders. The interior wall texture uses Phong, you might want to change this to None (same as Matte with default ambient and diffuse) to speed the render up.

To the radiosity processor this wood floor might as well be orange carpeting. I think the reason you might not see as much color bleeding with a real wood floor is that a shiny floor would bounce the majority of the light unchanged in a specular reflection onto the opposite walls and ceiling. The technology used in RW 12 does not do this kind of "specular caustic" - with radiosity things are treated as if they are all matte surfaces. Within this limitation the Diffuse parameter affects how much color will come off of the floor.

I would definitely use the area lights in the windows, otherwise this model is lit as if nothing but a bright sun and empty black space are outside the windows. The sun will shine through the area lihgt geometry; area light geometry casts shadows only if the light is set to render geometry and the light is off.

I would turn the Create Ambient option off if it is not producing the look you want.

I would set the directional and area lights to something around 500 lux to start with, then adjust them to get the proportionality you want.

HTH,

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Originally posted by Dave Donley:

I haven't yet seen the black triangle bug when rendering this file. Did this only happen after the 0% problem?

I can't remember Dave but I don't think so. There have been other strange geometric shapes, but I think they have all beeen after changing light or texture parameters and re rendering with the same radiosity settings (?)

]We have a bug report already about the solution not resuming after pressing ESC or after the time limit has stopped the solution. This is within the Custom Radiosity Options dialog. The workaround is to leave the dialog and then bring it up again. Did the 0% problem start happening after canceling the radiosity process?

Leaving the dialogue and reopening did not fix the 0% problems; only reopening the file

]I am seeing the window trim not casting shadows as in your rendering. I have filed a bug on this. I can get the shadows to be correct if I turn off the exterior trim for each window. It may have something to do with the wall splay and the trim together.

I hadn't even got to the trims yet ;-) the problem I see is the splay part of the wall/window object texture rendering not matching into the rest of the wall.

Area lights are slower with reflective shaders. The interior wall texture uses Phong, you might want to change this to None (same as Matte with default ambient and diffuse) to speed the render up.

I noticed that area lights are slow (I've tested since we last spoke) but I'm more interested in getting good renders.

To the radiosity processor this wood floor might as well be orange carpeting. I think the reason you might not see as much color bleeding with a real wood floor is that a shiny floor would bounce the majority of the light unchanged in a specular reflection onto the opposite walls and ceiling. The technology used in RW 12 does not do this kind of "specular caustic" - with radiosity things are treated as if they are all matte surfaces. Within this limitation the Diffuse parameter affects how much color will come off of the floor.

On the basis of my experiments so far, this means either: the wall and ceiling colours all wrong, or; the lighting all wrong, or; back to lots of work arounds to get it to look right. Not what I was hoping for.

I would definitely use the area lights in the windows, otherwise this model is lit as if nothing but a bright sun and empty black space are outside the windows. The sun will shine through the area lihgt geometry; area light geometry casts shadows only if the light is set to render geometry and the light is off.

This is the best I've managed so far with radiosity and area lights in the windows.

-

Still plenty of issues with colour/light balance -and artifacts in the far left ceiling junction. I'll keep trying.

I would turn the Create Ambient option off if it is not producing the look you want.

Well, actually, I think the extra light it adds after the 100% (even if it's not supposed to) is producing a more realistic lighting balance. Maybe thats something that could be taken advantage of?

I would set the directional and area lights to something around 500 lux to start with, then adjust them to get the proportionality you want.

The above example was: 4 area lights at 400% and Sun at 200%

I'll try Lux instead.

cheers,

N.

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This better be the last image for this thread; it must weigh a ton by now {:-O

it's starting to look like a brightly lit room now.

-

Dave,

Latest bulletin is I found a couple on new bugs (?)

1/ the Display colour coded preview stopped working. it would do it's render thing, and finish, but no preview would come up.

2/ if the Small detail is below about 300mm the blue triangles disappear

3/ the dark artifacts at the junction of the ceiling and walls are erratic. I did a render that had none; turned on the Ambient from remaining, they came back; turned it off again, they were still there. I can't work out how to reliably remove them. I'm thinking the Initial and Small detail would do it, but I'm not sure what I need to do.

4/the render previous to this I had the area lights at 400Lux and the Sun at 400Lux, but the sun on the floor wasn't bright enough. turned it up to 1000; no change, 2000, 5000; exactly the same result after recalculating. something wrong there.

The colour casts are still a problem that really needs to be addressed.

Now for the good news:

changing the sun back to % brightness at 300% lit the room well, but the seat cusion was too burnt, so I changed the floor reflectivity to Mirror (100%diffuse almost no mirror) and turned the sun down to 150%

The floor direct reflections of the sun are still a bit over-burnt, but I don't actually mind that: looking directly into the sun's reflection would be "like that" anyway.

More importantly; it's now starting to look like a brightly sun-lit room. We're not talking Maxwell Render here, but it's SUCH an improvement on RW11.

EJ,

the Radiosity solution was about 8 minutes with the following;

Textures and transparency ON

Ray tracing and Anti aliasing ON

Recursion 10

Curve detail LOW

nurbs OFF

Shadows Raytraced and transparent ON

Object inclusion 1.6m

Initial detail 804mm

Small detail 265mm

Accuracy 84%

Radiosity 100%

Halving all those sizes would send the Solution time into hours rather than minutes. I havn't even tried nurbs yet {:-/

The images were all screen captures and took about 15minutes or more to render. I think to output a print quality at 300DPI for a 3000 pixel image you would be looking at an overnight job.

The Area Lights are definitely the killer here. With the Sun on it's own, all those times are much much less.

cheers,

N.

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N, you're definitely closing in on the bugger ...

may I suggest a slight gray tint to the window glass... with perhaps an Imageprop of a distant skyline on the outside.

What is the dpi and how long to render ?

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You have a lot of patience and stick-to-itness to finally achieve what seems like should have been a simpler set-up. I am sure I would not have had the patience-the settings will be helpful if I ever attempt something similar- Thank you for the post

It does look great but the render times seem very long-you have a really powerful platform too- I don't even want to think how long it would take with my old weakling of a computer-no graphics card, slower processer etc...

I think I'll wait for an Intel machine to spend much time with this.

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Hi All

first, thanks to Nicholas for going to all this effort and sharing it with us.

I went to a seminar on rendering in Archicad, run by a very talented artist Dwight Aitken, and the basis of his whole argument was "think like a photographer". Have a look at the photo below;I assure you the walls and ceiling in my house are not Yellow/oragne. They are a pale beige.

-

Dwight's theory is that the human eye takes "snapshots" of a scene, and the mind blends them all into a memory of the space. So you look into a dark corner, and your eye adjusts to the correct exposure, you turn to the sun, and a second or too later, your eye has adjusted again. For your render to look 'right' you have to trick the renderer by faking the dark areas etc.

In Nicholas's excample, a professional photographer will add extra light to the scene to get the exposure correct in all the areas of the room. These lights are called the 'fill light', and the 'key light'.

Dwight posts a lot here http://archicad-talk.graphisoft.com/viewforum.php?f=3&sid=51852861849d04a35e6732ec14ab5366 and although it's not a VW forum, you may learn something.

Mat

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Hey Mat,

Fantastic render. must have taken you days to model the mother and child figures so well. ;-D

In fact, the whole scene reminds me of the minutely detailed domestic tableaus that the Dutch Masters were so fond of.

The mother attending the baby, the tot waiting for the telly to be turned on, the piles of freshly folded nappies, the piece of warped timber on the dining room table, the patched plaster on the pillar, the discarded ball on the floor........ and all so nicely composed. :-)

Oh, that's right; we were talking about renders.

Yes, there are strong colour reflections in your shot, and I'm concious of the unconcious amalgamation of static images that our minds perform to create our impression of reality. I spent a significant amount of the last 20 years working as a sculptor in the theatre industry and I'm highly aware of lighting, representation, and tricks, -and the observation of reality. I've spent most of my adult life Faking It. :-D

However; I'm sitting in a room with a floor like the photo, and (almost) white walls, and with the morning sun coming in through the windows, and the light on the walls is nothing like either render results, nor your photo. In your case, the fact that the walls are a beige (and not pure white as in my render) will be accentuating the colour reflections I would say. It is the degree of colour casts in the render that I am iffy about rather than their existance.

anyway, I'll go and check that link now.

cheers,

N.

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The parced plaster on the pillar is the result of employing a useless plasterer - I had to fix all his muckups myself.

Allways get a reference, or inspect a tradesmen's past work. Lessons you learn when building your own house...

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