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Comments: 4
davidbrinnen

08.08.2020, 20:57








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Indirect lighting in bryce MKI
Indirect lighting in bryce MKI

            

Indirect lighting in bryce MKI
Description: I've had my thinking cap on. Trying to think of a way to make it seem like light is bouncing around and interacting with objects within an enclosed space AND not take an eternity to render... So here's a little render box, with a couple of highly coloured walls. The scene is lit predominately with Horo's bluegreymoon.hdr - chosen because it is mostly white. I do like a bit of colour variation, otherwise I suppose a totally white hdr would do or a sphere of point light sources would do just as well. The set up is rather fiddly. For the final render (render time under 12 minutes - but the final image is a bit noisy and some banding I conceed), as I said, I used Horo's hdr at quality 64 with premium effect soft shadows rpp 4. Prior to that, I created a filter for each face of the enclosing box, this filter was made by rendering from the orthoganal views through the walls, ceiling and floor, which were made temporarily transparent and lit only with the two interior light sources. The resluting renders I then applied to "slides" 2d faces which I placed outside the walls of the box and made it so that the walls of the box did not cast shadows. The idea being that by illuminating the box from the outside with IBL the filters would allow light through where the walls were lit by the inner lights making it look like the light from the light bulbs was being evenly scattered by the inner walls. Sort of thing.
Added by: davidbrinnen
Keywords: davidbrinnen, bryce6.1, IBL, hdr, Horo, indirect, lighting, MKI
Date: 05.13.2008 16:30
Hits: 2371
Downloads: 69
Rating: 0.00 (0 Vote(s))
File size: 53.2 KB
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Author: Comment:
rashadcarter1
Admin

Join Date: 06.04.2006
Comments: 2622
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I'd say overall this is looking good. You have managed to create something that looks like indirect lighting resulting from the direct light bouncing off of the walls. Great!!

But my other fears are also confirmed, which is that the hdri from outside cheat does not provide light that solves accurately for the specific room we are in. I will explain. But not too much here as RenderMan started a thread in the User Forum about bouncing light where we can go into more detail. Also David, I tried to e-mail you an example of the spotlight idea but your mailbox would not accept it, too large nearly 15mb. Anyhow on to your scene.

Ambient Occlusion is a very important part of a GI simulation. Ambient Occlusion is what gives us the feeling of gradient along a wall surface fading from lighter to darker. It is a geometry fixer. In reality, a wall is not evenly lit, it will almost always be slightly darker near the corners. What is missing above is that extra shading of darkness that should be wrapping itself around the edges of the walls. The issue comes in that the hdri is just too even, the light is just too well balanced and it illuminates areas that should have been left darker. Also, the blue floor should be reflecting some blue light onto the bottom of a sphere. You can disable the shadows of the ground plane or even use a spotlight.

Also, if you were to carve a window into this room you would need the walls to cast shadows and the hdri cheat would no longer be feasible. This is another reason I have hesitated to place confidence in the hdri cheat. But I will also say that as a time save the hdri cheat seems very feasible and the result is far and beyond most other indirect light methods like ambient channel glow.

I often indulge you David so I am curious if you might indulge me once. The idea is that you might consider as a test the spotlight idea. It only requires 6 spotlights, one for each wall. You will need Premium AA to solve the noisiness of the soft shadows I am proposing. The idea is simple, using flattened spotlights with edge softness set to 100% and soft shadows set to 100%, and fall-off set to squared. Place a flat spotlight at the center each of the six walls facing toward the interior of the room. Clearly the red wall needs a red tinted spotlight and vice versa for the other walls and floor. You must play with the intensity of the lights. The spotlights need to be very flat maybe only 0.2units in "height" but very wide maybe 100 units. It should look like a pancake. Also the spots should be placed as close to their assigned walls as possible but not too close or you will see the narrow end of the spotlight being visible for some reason. Please see this link for an example of the finished product:
http://www.bryce5.com/details.php?image_id=3045&mode=search

I cannot promise it will render as quickly as the above example due to the necessity of premium AA, but I can tell you that it will give you a more specified light solution and in my opinion a more flexible approach that will work in all situations, not just windowless rooms. You will notice due to the edge softness of the spotlights that the corners of the room fade to dark just as ambient occlusion would produce.
05.13.2008 17:34 Offline rashadcarter1 rashadcarter1 at aol.com
davidbrinnen
Admin

Join Date: 01.03.2004
Comments: 2227
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I am happy that using the spotlights technique is sucessful, you have already demonstrated that. Your objections show that I have failed to both explain and demonstrate what I was aiming for. Each side should indeed illuminate the interior obects correctly per colour and it should be possible to cut a hole in the wall, because each "filter" for the wall casts a shadow, the red wall casts a red shadow where it is illuinated by the light, probably I used too bright a light which is why the corners are not darker... Not sure of that without testing. Also, if a hole were cut in the wall, that should cut a hole in the rendered filter. Again I should have to test. Aligning the shadow colour filters with the walls is tricy and the main drawback with this is that the use of the orthogonal views dictates the angles of the filters. This I am pondering now. Sadly the copy matrix function is a bit flakey with the camera, it seems not to map the exact point of view to the centre of objects which is a problem when very precise overlaying of lights is needed.

Oh, my email will only accept 10mb I think...
05.13.2008 18:23 Offline davidbrinnen mail at davidbrinnen.co.uk http://www.davidbrinnen.com
rashadcarter1
Admin

Join Date: 06.04.2006
Comments: 2622
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I think your technique is absolutly plausible in the way of bleeding the colors from one wall onto an other. That part is not my objection. It is only in the evenness of the light. I am testing out my suggestions to you as we speak to see what kind of result I can attain and at what render times.

I think it comes down to deciding whether to use ibl lights arranged around a sphere, or spotlights with soft shadows along the walls. the purpose of both is to create the idea of light coming from many points on a surface and not from a single point. Likely we are after the same effects.

Also, the spotlights are tricky as hell also. I am not completely convinced by then either, and likely a combination of hdri and spotlights would be ideal for realism though likely a boon for render time.

I just can't get Carrara out of my head as we run these tests. I really wish they would find a way to write GI into the Bryce render engine so that we would not need to rig such things manually with tricks and approximations.
05.13.2008 18:35 Offline rashadcarter1 rashadcarter1 at aol.com
davidbrinnen
Admin

Join Date: 01.03.2004
Comments: 2227
-

Agreed on many levels and for the same reason also, since I have sampled the evil delights of Carrara - GI and indirect. So yes, understand I am not dismissing your spotlights because they do not work, but for the reason that you have already made them work. This MKI is a cludgy way of doing things, accepted, but it's given me an idea. Good or not, experimentation will determine.
05.13.2008 22:22 Offline davidbrinnen mail at davidbrinnen.co.uk http://www.davidbrinnen.com
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