Faking Global Illumination in Carrara
Rashad Carter
Posts: 1,799
What's up!
In this thread we are going to examine a couple of principles for faking Global Illumination in Carrara. Even with our faster computers of today, we still need to fake the GI from time to time. Fake GI, while not quite as real looking as Full GI, can often come close enough to be acceptable and can often render in half the time or less.
We will examine both Indoor and Outdoor lighting scenarios as separate studies.
We are looking for a best compromise between accuracy and speed. But we should also know not to expect miracles.
**Fake GI no matter how well implemented will almost never look as good as Full GI
***Biased GI like that of Carrara will almost never look as good as Unbiased Rendering like that of Octane
The idea is to make the best of the given approach, without setting unreasonable expectations. Fake GI can always be made to look better, and as such it's render time can sometimes climb until it converges with real GI. But even when Fake GI takes as long as Full GI, the Fake GI still allows for more user control, by allowing for excluding hair and the like, to super-speed rendering complex scenes.
Download the Files included here to participate directly in this thread. Scene files are from Carrara 8.5 pro 64bit. Apparently the scene is backwards compatible and opens reliably in Carrara 7.2.
Indoor
Sunlight Only
https://drive.google.com/file/d/0B4IpzCJ1fXpebGh5alJELUJKdjA/view?usp=sharing
Sunlight + Ceiling Lights
For C7.2
https://drive.google.com/file/d/0B4IpzCJ1fXpeVjNocEJvMnYzajg/view?usp=sharing
For C8.5
https://drive.google.com/file/d/0B4IpzCJ1fXpeSGJtb3BiMzg0d0k/view?usp=sharing
Outdoor
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Comments
Indoor
Here are three ideals to consider:
1. Respect for the Sun
It is usually a good idea to start with a plenty powerful Sunlight. Don't be afraid to crank it up far beyond the default 100%. Time of day is essential and knowing how much to soften shadows and for what color to tint the Sunlight. More on that later.
2. Spotlight Mapping
Spotlight Mapping is when one manually maps the surface of an object with traditional spotlights to model the effect of light being reflected off of that surface. Typically, you want to allow the spotlight to cast light in a full spread, a full 180 degrees. You also want to carefully adjust fall-off ranges. But more on that in a moment.
Spotlight Mapping is essential in creating the illusion of bounced Sunlight along a wall or along the floor. In the example scene provided, Spotlight Mapping has been used to model the Sunlight that should be bouncing upward from the ground and the floor upward toward the ceiling. Typically, surfaces that become very bright from direct illumination by the Sun often need to be mapped with spotlights to represent the significant contribution their reflections would make to the scene.
3. Indirect Light Simulation
In Full GI all surfaces are treated as potential light sources. When faking GI we need some manner of accounting for some of that bounced light between surfaces.
In Bryce 7 Pro we have a tool called the 3D Fill Light, which basically creates a "volume" of virtual point light sources casting light and shadow rays in all directions. The results are very nice, doing a good job of approximating indirect light bounces as well
as providing the shading necessary for a fully 3D result, thus the original name.... the 3D Fill Light.
While this sounds as if it would produce results exactly like that of Ambient Occlusion, it actually seems that the 3D Fill Light does a better job of faking Indirect Light than Ambient Occlusion. More on that too, in time.
Carrara does not have an official 3D Fill Light feature at this time, but it doesn't matter because they can be rigged quite successfully in Carrara via Replicators. In the provided example, the custom made 3D Fill has been carefully modeled to fit the interior volume of this room.
Below are some examples. Click for full view.
It is important to note that both of the Carrara renders can be improved. The issue is the rendering speed trade-off. All of these renders were intended to be kept under 20 minutes on my 8core Xeon / Dual Titan Black system. My rendering times may not be typical for some but they should scale more or less predictably.
**The Octane version is the Physically Correct reference by which we should compare the other two.
Continued with the next installment.
The download links to this installment are included in the original post. There are two different versions, as the 8.5 version has Octane materials assigned so the scene is not fully backward compatible with 7.2.
This time we will examine the look of the scene after adding the influence of the ceiling lights with what we already had. Once again there are three renders, first is Octane that we will use as a reference for this exercise. The second is Carrara native Full Indirect Light and the final is Faked GI.
In this case the difference in rendering time is significant. Octane has a much more difficult time resolving the noise down to an acceptable level. It took an hour and a half on my dual Titan Black system. Part of the issue is that really small light sources are unlikely to be struck by the randomly fired rays when only a few rays are being used. So to resolve these scenes a lot more rays and time are required. There are several really nice effects such as the caustic light bounce visible on the left part of the ceiling above the floor lamp. I assume it is a reflection from one of the ceiling lights on the shiny metal of the lamp. This sort of interaction is why I love unbiased rendering.
By contrast, the Carrara Full GI version took a little longer than the no ceiling lights version as well roughly half an hour, but it also diverges greatly from the Octane reference. Color transfer as well and overall light propagation are vastly different. There are a lot of settings I could engage to improve this full GI render, but the render time cost climbs considerably and quickly.
One of the issues is that I am so far unable to model the light source so that the light spreads evenly outward the same way in Carrara as it appears to do in Octane. In both of the Carrara versions, there is visible banding along the ceiling where the various shadows cast by the ceiling lights are interacting with their individual holders. It is forgivable I think, but still worth noting
In the Faked GI version, I am able to manually tweak the lighting so that the result matches up much more closely with the Octane reference than the Carrara Full GI version does. All of this in under 10 minutes. The render time has not been affected too greatly by the addition of the ten ceiling lights.
I took EvilProducer's advice and set the brightness of the 3D Fill object to just 0.7, allowing me to increase the brightness of the color I have in the color chip. I also have gotten a bit better with adjusting fall off ranges and the like so the 3D Fill should look even better in this installment than in the first round.
As always, feedback is greatly appreciated. Thanks all for your time
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(is this a game?) :) :)
Very funny. I'm still chuckling. Not a game as such, I just wanted to leave myself some space to upload examples. Over the next day or so these tiles will be filled in. See ya in a bit.
I guess I had better put on my reading glasses.....
There's only one other person here that can challenge Dart for most verbose! ;-P
Is it wrong to post an entire novel in a response? I though we all loved reading novels.
Hopefully the visual examples will do the heavy lifting, since the treatise has already been written in another thread. Statements need backing up with real examples. Fun fun!
I've got to tell you Rashad, I've been playing with using a replicator and some bulb lights to make a more 'mesh light'-like lighting rig and it looks pretty great in renders. Also, there's nothing that says we couldn't use this method with Global Illumination too to make even more excellent renders. I'm very very happy I caught your discussion in the renders thread about this, and looking forward to learning more about the method :)
Is it wrong to post an entire novel in a response? I though we all loved reading novels.
Hopefully the visual examples will do the heavy lifting, since the treatise has already been written in another thread. Statements need backing up with real examples. Fun fun!
No worries. I'm just kidding. When Dart, Garstor and I, met up a couple summers ago, Garstor and I gave Dart so much s h ! t about talking like he typed. It's all meant as good natured ribbing.
No worries. I'm just kidding. When Dart, Garstor and I, met up a couple summers ago, Garstor and I gave Dart so much s h ! t about talking like he typed. It's all meant as good natured ribbing.
No need to explain, I know we are having fun with each other. The real fun begins once the uploads start.
I must say, Carrara really is a very capable program. I love it more and more.
You would need to be extremely careful with that method Jon. Remember that Indirect Light calculates all those light sources for the reflected lights. The more lights, the more calculations.
Where that would work nicely would be a partial GI, such as Skylight, where the light is generated by an HDRI, or a Realistic Sky. The light would come in from all angles, like atmospheric light, so it gives a GI look to to an outdoor scene. The problem is that the light does not reflect off of one object onto another object like Indirect Light. But let's say you have a park scene, and part of the scene is under a park shelter. This is where that light rig you referenced would really shine (pun intended). It would give a nice GI diffused light look under the shelter, where normally it could be too dark.
You would need to be extremely careful with that method Jon. Remember that Indirect Light calculates all those light sources for the reflected lights. The more lights, the more calculations.
Where that would work nicely would be a partial GI, such as Skylight, where the light is generated by an HDRI, or a Realistic Sky. The light would come in from all angles, like atmospheric light, so it gives a GI look to to an outdoor scene. The problem is that the light does not reflect off of one object onto another object like Indirect Light. But let's say you have a park scene, and part of the scene is under a park shelter. This is where that light rig you referenced would really shine (pun intended). It would give a nice GI diffused light look under the shelter, where normally it could be too dark.
Agreed. Carrara's native GI is more than capable of deriving an acceptable solution. The lucky benefit of having the Octane Plug-in is that I can directly compare the way the various engines render the scene so the points of divergence from accuracy can be more easily noted.
No worries. I'm just kidding. When Dart, Garstor and I, met up a couple summers ago, Garstor and I gave Dart so much s h ! t about talking like he typed. It's all meant as good natured ribbing.
Dart talks exactly like he types? I'm picturing that in my head and wondering how you guys ever got a word in edgewise :) I bet he was a blast to hang out with, if he's even half as positive in person as he is on the forums.
He's great. We had a great time hanging out. Sadly it was far to short.
Edited to add a link to avoid hijacking this thread any further:
http://www.daz3d.com/forums/discussion/29797/
Apologies Rashad.
I've included a file in the Original Post for download so we can get the discussion underway. I look forward to hearing feedback.
WHAT??? EVIL IS A YOUNG GUY?? NO WAY !!!!!!! :) :) :) :)
I'll be honest, I had you all wrong dude. And you have blonde curly hair????
Okay, dude, seriously, you're not evil at all. You need to change your name. How about "NiceGuyProducer"? :) :) :)
Well done, Rashad :-)
WHAT??? EVIL IS A YOUNG GUY?? NO WAY !!!!!!! :) :) :) :)
I'll be honest, I had you all wrong dude. And you have blonde curly hair????
Okay, dude, seriously, you're not evil at all. You need to change your name. How about "NiceGuyProducer"? :) :) :)
I'll be 47 thi year, so I was 45ish then.
Wow, dude, I'm jealous. I guess the fresh air and rural living in Wisconsin must be really good for you. I never would have guessed 45.
I realize that you've just started posting your tutorial, and I don't want to take away from the great work you're doing, but I do want to put my 2 cents into a misconception that I think many folks have.
Not Octane, or any other renderer, is necessarily Physically Correct. And the only physically correct reference you should use if you are truly interested in "realism" is a good photograph.
I find a lot of folks tend to judge "realism" of a render using nothing more than a "looks good to me" evaluation. But unless you can use a really physically accurate image (ie, a photograph) then you are judging a fake using another fake.
And I'm sure everyone is aware of this, but just because an unbiased renderer, such as Octane, might be "physically based", that doesn't mean it's "physically correct".
And the reason is this:
A physically correct render requires more than just a good renderer. It requires excellent implementation of materials and surfaces, as well as lighting (color, intensity, diffusion, etc.). And those things are INCREDIBLY complex.
And with all due respect to the Carrara scene being used as an example, the lighting and surfaces and crisply-perfect models provided by DAZ in that scene are pretty horrendous, and scream "CG", no matter what the renderer.
So while the lighting concepts I believe you are going to describe are good ones, I just want to caution folks that if they want others to really appreciate your work, you need to look past the rendering methods and lighting methods for the entire toolset which goes into a really physically accurate render.
And in the years I've been in this forum, I can't recall ONCE anyone comparing their renders with a photograph.
Just my 2 cents... :) :)
And BTW, I've seen MANY incredible renders coming out of unbiased renderers like Octane. But at the same time I've seen many many horrendously bad ones too, with people claiming they look "realistic".
Again, the renderer is not the magic button for realism. It is whether your skylight is modelled correctly. And whether your man-made lights are modelled with the correct angular intensities and nonlinearities, and the correct color spectrums, and the correct diffusion of their bulbs, and on and on. And whether all of your surfaces are modelled realistically, including colors and bumps and skin SSS and reflection. And the list goes on and on.
Yes, a good, physically based renderer is a big help. But it only solves less than 50% of the realism problem. :) :)
Wow, dude, I'm jealous. I guess the fresh air and rural living in Wisconsin must be really good for you. I never would have guessed 45.
It's the cheese. ;-)
I agree about the bad renders from un-biased renders. I remember when Reality came out for Studio, and there were so many.... :down:
Rashad, I notice that in your examples, the picture with the replicated lights looks much warmer. Are you using a color, or the default white? Also, what is the intensity, range, and falloff?
And speaking of skylight, I hesitate to recommend this since it will probably induced a glassy-eyed snoring in most folks :) :)
But if you can ignore the equations and stuff it's a good technical paper that gives you a little idea of how developers implement stuff like Carrara's Realistic Sky, and what they have to consider in order to simulate all of the skylight parameters. And it gives a good basis for understanding the stuff you need to understand to fake sun and sky light, and all the complex stuff involved in something that might seem pretty straightforward.
It's a very old paper, from back in the 90's when this stuff was first being developed and I was reading technical stuff like this trying to understand how it all works. But it's got some good stuff in there, FWIW
http://www.cs.utah.edu/~shirley/papers/sunsky/sunsky.pdf
Car problems today, so called in, which means for a little while I'll be able to comment....
Anyway, Joe's comment on the skylight (thanks for the link), got me to thinking about a comment Rashad made in his post about sun brightness and color.
If you use the Realistic Sky, and the sunlight together, you lose control over color and shadow intensity, but what you gain is the ability of the sun to change color depending on the angle. Also, it seems that according to my observations (could be wrong) that the atmospheric haze and such reacts more "realistically" than it would if just a plain distant light is used.
BTW, a Realistic Sky can be a render time friendly way to add depth to a scene- even a large, cavernous interior scene, by using a bit of atmospheric forced perspective using the haze and fog controls.
It's the cheese. ;-)
I agree about the bad renders from un-biased renders. I remember when Reality came out for Studio, and there were so many.... :down:
Rashad, I notice that in your examples, the picture with the replicated lights looks much warmer. Are you using a color, or the default white? Also, what is the intensity, range, and falloff?
Yes, the lights are color tinted to a degree. I tested it and it turns out the files open just fine in Carrara 7.2. You can download it yourself and see all of the settings.
Magaremoto,
Thanks! That means a great deal coming from you.
Yes, the lights are color tinted to a degree. I tested it and it turns out the files open just fine in Carrara 7.2. You can download it yourself and see all of the settings.
Magaremoto,
Thanks! That means a great deal coming from you.
Interesting choices for the color chips. I'm trying a quick render with my own idea to see how it works.
Just to offer a suggestion for the render room: I don't know if it effects the time it takes to render, but you don't need to enable the Compatibility Shadows mode. If I recall correctly, that was put in there to enable people to correctly render scenes created in older versions of Carrara, such as version 5 or earlier. I believe it had to do with a change in how soft shadows were implemented.
Thanks. I did not select that myself, I loaded this scene from the included presets and made a few modifications. The one thing I did set was Gamma 2.2. The results are far better when this setting is enabled.
I'm on a Mac, so I'm using 1.8 Gamma. I don't usually use it, but I figured, what the hell. Try and keep thing similar.
What I've done for the lights and the tint, is that if it looks to bright with my selected color, and the number of replications, is to lower the light intensity. Even though it doesn't display, you can enter decimal values. I have used a light dome where I typed in the brightness value of .35 or something similar. After hitting enter, the value shows as 0, but many renders confirmed light was being generated, as ambient was off and no other lights were in the scene.
Maybe I'll try that out next....