Fill Light and Shadow
Electro-Elvis
Posts: 883
I am experimenting with fill lights lately. And I asked myself, in which situation should I activate the option "cast shadows" in the light lab? I think for illuminating a room with a constant amount of light (what I feel is the purpose of fill lights) it is better to switch of "cast shadows". But maybe I am missing a point?
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I'd switch off shadow casting for every fill light you use, and only use shadow casting for items in the scene that give off direct light. Things like lamps should have shadow casting on, but not fill lights unless there are a few of them and you make the shadow intensity very weak and blur the shadows.
Absolutely no sharp shadows from a fill light, that's for sure (in my opinion anyway).
Classical Fill lights are totally different than the 3D Fill Light offered in Bryce 7 Pro. In classical photography, a fill light is merely used to add more light to the shaded areas of a shot. In the real world light already bounces around surfaces, but in Bryce they do not unless one is using TA. So the 3D fill in Bryce has to do more than just fill in shadows.
In a nutshell, the 3D Fill is your answer for indirect lighting for interiors. The 3d fill is a cluster of radials floating around within the volume of an area. Unlike Domes and IBL which arrange virtual radials around the outer perimeter of a sphere, the 3d fill by comparison occupies the internal area. It is similar to the way air molecules fill every corner of a room. so does the 3D fill place dim virtual radials around a room even filling in the corners.
A 3d fill is basically a manual approach to ambient occlusion for interior scenes. Notice the occlusion. Light without shadow is useless. The 3D Fill arranges virtual radials to float around the area of the wireframe object in a somewhat random manner. The purpose of so many lights is to gain lots of light ray perspectives. For an object to look fully 3d, it needs light to illuminate it and shadows to give it form and shape. Light without shadows will result in formless, flat looking objects. This is why material ambience is so bad, it doesnt give shadows so it flattens the render.
So again, in real life light already bounces around all surfaces. But in a Bryce scene they do not. The random floating radials of a 3D Fill represent the light that should be bouncing around all of the surfaces of a room. The floor, ceiling, and all 4 vertical walls would reflect light in real life. But also the tables, chairs and other items within a room also reflect light. The 3D Fill can provide a nice general indirect light and it also provides dim shadows from multiple angles, which also adds depth and realism to a scene.
So in a nutshell a 3D Fill can be used two ways:
A. As indirect light. If you place the items inside the wireframe of the 3D Fill, it will cast light onto all sides of the target model placed at the fill's center.
B. You can also use them as fast rendering soft shadow key or direct light sources by using them instead of a radial. Obviously, the target items cannot be placed inside of the fill if the fill is intended to be used as soft shadow key light.
Here is what you should do.
1. Create a Cube in Bryce. Make it large enough to be a room interior.
2. Create a Cube 3D Fill Light. Fit it inside of the Cube so that they are the same size.
3. In the Light Lab of the 3D Fill, switch to Gradient instead of Uniform Color
4. With the gradient, you need to invert the polarity of the gradient so that the white and black ends are switched. Exit the light lab
5. Now create a few random objects to place within this room. Try a sphere, a cube a torus, and place them randomly within the room.
6. The only light in the scene should be the 3d Fill. No radials, no ambience, no ibl at this point.
With only the light from the 3d fill in the room you will notice that the objects in the room are dimly visible. It should look like an overcast day inside of the room.
The 3d fill just like the Domes can be adjusted for bias and randomness of the way the virtual radials are arranged. But 3d Fills also can adjust distribution. Distribution determines the placement of the virtual radials in terms of how close or how far from the geometric center of the Fill. In theory, the lower the setting for Dist, the closer to the outer edges of the wireframe you will find the virtual radials. At a lower setting the radials will cluster near the center of the fill, behaving more like a single point source.
Why the polarity switching of the gradient in the light lab? Well, a 3d fill operates by placing floating radials in an area, not around a perimeter. Typically, all lights have a fall off where the light emitted gets dimmer with distance. This means that when a radial gets close to an object the object surface will display a sort of "hot spot" or area of brightness. Since we are faking indirect light not direct light, we need to avoid the hotspots that will arise from the virtual radials which come into close proximity with the items you have placed within the scene. Thus the polarity switching of the falloff gradient.
Also, It is possible to use too much distribution and you will find that the virtual radials of the fill are outside of the room or clustered into a ball at room center. The default setting is usually fine.
I will be back soon with some images to explain how this works. Back in a few.
Yes, this is true. Luckily the shadows cast by a 3d fill are already softened by nature due to being comprised of multiple points, that is why it is actually best to leave shadows enabled. Even with hard shadows enabled, the result will still be soft because of the multiple points. Thus it is a major waste of render time to enable the soft shadows option on any cluster light form such as domes or fills. Anyhow, back to why the 3d fill needs shadows to operate optimally. Otherwise the only shadows cast will be those cast by the key light. While key light shadows are important, the less obvious shadows cast by the indirect light of a room are equally as important.
The good thing about TA is that it does all of that light and shadow bounce calculation for the user. The 3d fill requires more manual labor but can be a great time saver compared to TA in certain situations.
The alternative we used back in the Bryce 6.1 times was random multi-replicate radials with inverse gradient.
Here is an example of a scene rendered with only the 3D Fill. There is no direct light, only indirect light from the 3D Fill. Notice how there is light, but there is also shadow to carve out the physical details of the simplistic models in this scenario.
Edit: Right Click and Select View Image to see this image at full resolution.
Edit: I should state that the light in this room currently does not make sense physically. We have indirect light bouncing around a fully enclosed room but we have yet to introduce any key lights. We have the "effect" before we have put forth the cause. So now I will add key lights and I will leave the 3d fill levels exactly as they are now and the image will make physical sense. Back in a while.
@Rashad: I'd be qiuite interrrested in the settings for the fill lights in that render. Maybe even interrested enough to run Bryce on my old and slow pc again. Havnt tried Bryce in a long time since it won't run on my Mac.
I cannot imagine what sort of a pickle we'd be in with this light tool if you'd not discovered the inverse gradient solution for hotspots problem! You literally salvaged it. Thanks so much I must say.
Indeed. I will upload a list of settings in a short while. I have another sample render baking currently so I will be back soon with settings for both renders. In the mean time you can download these 6 sample scenes on ShareCG:
http://www.sharecg.com/v/50615/gallery/5/3D-Model/Fake-GI-Interiors-Resource-1
http://www.sharecg.com/v/50616/gallery/5/3D-Model/Fake-GI-Interiors-Resource-2
These downloads include 6 different ways to go about illuminating an enclosed interior in Bryce 7 Pro. The approaches are very basic and easy to understand, or at least I'd like to think so.
If you are going to run it on a slower PC then try to use a lower quality setting. Remember too that the Shadow Intensity setting in the Sky Lab affects 3d Fills as well. If you lower sun shadows to 50% you also weaken the shadows of the 3D Fill by 50%. For this reason i find it best to always increase sun moon shadows to the maximum and adjust the shadows of my 3D Fill within the light lab as needed.
Oh, thanks Rashad. We have this saying: "Even a blind hen finds a grain now and then".
Hi Rashad
Thanks a lot for your detailed and clear explanation. Very helpful. And all the other for the discussion.
In the meantime I have made a few more tests.
Picture 1: Fill light with shadows
Picture 2: Fill light without shadows
Picture 3: No fill light but TA
Picture 4: Fill light with TA
Picture 5: Fill light with TA and TA optimization.
I think, picture 4 delivers the best result, but the render time is very high. More than 14 hours for such a small picture.
Picture 5 has a good render time but is I am afraid crap. I think TA optimization does not work properly.
Picture 1 is a good compromise between render time and realism.
Nice work Elvis! Great demonstration. Typically, one does not need to use both a fill light and TA. Usually one would use one approach or the other. The reason is that TA slows down the more point sources you add to a scene. A 3D Fill is comprised of multiple virtual point radials so they automatically cause long render times when used with TA.
I'd say that the most realistic version is probably number 4, but I'm sure the render time is long. TA Optimization is a different beast altogether, requires boost light to operate properly. We can go into that if we want. But as you observed the Picture 1 looks just fine and has a good render time as well. A 3D Fill alone can do it more or less acceptably.
Edit:
Actually, Number 3 is pretty good as well. it is a TA only demonstration and TA is quite amazing. The strong blue color cast gathered from the sky is accurate. it gives a clue that you might want to blue tint your 3d Fills a bit. I often will render a scene with TA as well as with fake GI to see the difference. If I can tweak my fake GI to look as much like full GI as possible that is what I tend to do.
Horo-
But this hen did more than just find a grain. No exaggeration but to my mind the inverse gradient solution for 3D Fills is about as clever and life altering as discovering a cure for cancer for biology. Without your trick we'd have nothing.
As promised to Dyret, here are the details of the sample render i provided earlier. There are settings for the 3D Fills used as indirect light and for the Domes used as Key lights.
It is important to note that the results can be very fast. At lower qualities the renders are speedy. 3D Fills are similar to IBL in that shadow banding can become a problem at low quality settings so it really depends on the situation. The comparison renders demonstrate how much more render time is needed to smooth out the illumination.
Feedback is appreciated..
I'm having trouble uploading the next series of images. I will give it a few minutes and try again.
Elvis,
There are a few tips to using the 3D Fill that I will mention.
First, it is important to make the 3D Fill to occupy as much of the interior volume as possible,. You must fit the 3D Fill both vertically and horizontally into the cubicle you have carved out or built up with walls. As you see from the examples I uploaded the 3D Fill nearly touches the walls on all six sides of the room.
Second, there is a slight bug with the 3D Fill that must be corrected. The problem is that the virtual lights are not perfectly equidistant from the object center. Kind of like the triangulation of the centering is slightly off. The result is a sort of bias where some walls of a room receive a little too much light while others a little less than they should. The solution is to use a second 3d Fill, but to rotate it by 180 degrees along the Y axis. This step corrects the off centering perfectly.
Bias pushes the lights toward north and south. For Horizontal biases you want to tilt the 3D Fill onto its side.
Lastly, 3D Fills like Domes can be used as GI for outdoor scenes as well. You can make them infinite in size if needed by using the Distant Option. But you can also shape them to fit any dimensions you may need. In a dense forest IBL and domes might have a hard time penetrating the overhead canopy, but a 3D Fill can be placed down near ground level and shaped to fit and provide all of the needed indirect lighting..
3D Fills are seriously awesome light sources!!
thank you Rashad. Going on hollidya with only my Mac for a couple of weeks. I saved the pics so will play with this after holliday. Your resluts are really starting to look real :-)
Curious to know how these lighting projects are doing?