Ambient Light on Scene and GI together?
digitani
Posts: 10
Does anyone have an opinion on using the ambient light property of the scene and GI together? Do they play nicely?
It is looking to me like they might play nicely together if you want GI, but also want to force a lower limit to how dark any shadows can get, but at the same time, I feel like the render gets a little more grainy when I put them together. Not sure if I'm imagining or not.
Anybody have an opinion from their experience?
Thanks guys!
-digitani
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Comments
The graininess may have more to do with the AA settings. If you're talking more about blotchiness in the shadows, then that's the Photons. You may have luck getting rid of the ashy look by increasing the amount of photons, your photon map accuracy and the quality.
Most things I've read, and my personal experience suggest that it's best to turn it off when using GI. Using ambient light with GI can run the risk of making the lighting look flat. You may have some better luck with GI and no ambient light by enabling gamma correction in the Render Room. PhilW Has a thread about how to get your most realistic renders ever by using gamma correction set at 2.2 for Windows (1.8 for Macs). There's also some good information about using a linear workflow. I think the title of the thread is a bit hyperbolic, as gamma correction can't really help in all cases, nor should it, and also if the lighting is bad to begin with....
http://www.daz3d.com/forums/discussion/25644/
The original intent of ambient light was to speed up renders by faking a GI effect with ambient light. In my opinion, you're better off simulating GI by well placed lights, as ambient light is a uniform light strength and color. There are times when it can be useful, but in many cases. less is more, so start at low settings and go from there.
Ah, I have never learned about the photon settings. I'll play with that as well as the gamma correction.
Thanks so much for such a great answer!
The photon settings and quality settings, radius, etc. are really scene dependent, so I can't really tell you the best level to start at. Personally, for those times I do use GI, I start with the defaults and go from there. I have found the darker the scene or the more areas where there are deep shadows is when the ashiness rears its ugly head.
That's interesting about the gamma correction, EP. I'm gonna sit down and read that thread right through later (38 pages is too long for "over breakfast!"). Although I'm sure "Gamma correction 2.2" is a phrase that I've seen bandied about, I hadn't been aware of a different value for Macs (since I'm a Mac user).
I only watched the lighting chapter of Phil's tutorial yesterday - he had a big section on ambient lighting, but I don't think he mentioned GC.
gamma correction has nothing to do with the problem you are asking. its best to leave it at its default setting. on a side note carrara saves renders in srgb and a gamma of 2.1 standard for a pc monitor. i tried a render with gamma correction at 1.8 standard for macs, cararra still saves srgb and a gamma of 2.1. i expected a render of rgb and gamma 1.8. im wondering if it even works
The gamma correction issue isn't related to the OPs graininess question, but rather the ambient light question. Everything I've read says that you should avoid ambient light when using GI. I can't really speak to what Carrara does with it's internal files and such and what the gamma is or isn't doing. I'm just pointing out some information about a possible way to help his lighting. If you look at the thread, you'll see that my position is that it is scene dependent.
From the way I understand it, is that the Ambient slider in the scene settings is a replacement for the more time-consuming Indirect Light, in the Global Illumination settings in the render room. It is a cheat that lowers the intensity of the shadows, like you've observed, but is the same across everything, whereas IL is calculated according to anything that is capable to reflect light in the scene. With IL, anything that can reflect (commonly referred to as 'bounce') light, which is any object, depending upon its shaders, then becomes a light source - again, according to its shader settings. With IL on, a glow channel setting above 100 actually becomes a light emitter.
This is where you can really bog down your render times, but can achieve amazing realism.
Here is where the raytrace levels make the big difference, as that number will determine how many times each ray will reflect (bounce) before it stops calculating. The default in the render room is 8, and reflection in a shader defaults at 2 or 4, I believe. The shader I'm looking at is on 2. This number may need to be increased if it is so reflective that we should be able to see shadows in it. That, right there, is the big example of what that does - how far into reflections the ray tracer needs to calculate them, and their appropriate angles, softness, etc., which can put a lot of strain on your computer. That's, after all, an awful lot of computing!
Most of today's multiple core cpu computers can handle this rather well, but it still takes time. All of this time is spent with your cpu cores running wide open, so make sure that you have plenty of airflow - keep the intakes clean.
evilproducer taught me to set the irrandiance map to "One for all frames (static scenes)"
I'll have to investigate this more, as I normally use an All Cheat method of lighting, where I don't use GI or IL, but light everything to taste, by hand. But I'm still very interested in learning this stuff, since Carrara offers it so nicely. I'm not sure if this means that one irrandiance map can work if the camera holds relatively the same angle, without pivoting along the z axis, around the subject, or what. But it makes the entire calculation fling by very quickly compared to the default value of "Calculate at every frame". I'm not sure what Interpolation does, but I've been advised by more than one, that I should deselect it too, which is selected by default.
Scene Ambient Slider:
It is suggested by all of the lighting gurus I've ever spoken to, to turn this completely off. It is then suggested to use "Bounce lights" to fake IL, when IL is not used.
Artificial Ambient Lighting using Light Linking:
The great advantage of using light linking as a cheat as opposed to IL, is that you then have full control over the colors from various directions, you can individualize colors to specific objects, and you have a much higher level of freedom for all aspects of the shadow properties.
This method takes more time per scene to get it all set up right, but then takes very little time to adjust for individual needs, even animated changes. Let's say that your client (whom it is doubtful that they will know anything about lighting a digital scene - so their request will have to be translated by you, who does understand) agrees to proceed, but only if you can get it to look less bluish and more orangy. Well you might immediately know the solution, knowing how the lights are set up. But if you're using a single light source and full GI with IL, you may have to really sit down and thing hard about how to approach such a change, as it's all been calculated for you. Just as a short, less wordy example.
The animated gif I posted here uses GI plus full IL. Well, that post has a good description of the settings, so I'll not bore you here with that ;)
Hey Dart. Very informative post. There is one inaccuracy that I know of. The glow will act as an emitter below 100% on a numeric slider, but the effect may not be visible as brighter lights could wash it out. You can test it by making a darkened room and sticking an object with glow in there and play with the brightness levels.
My suggestion would be if you wanted a glowing object as a light emitter for some kind of photo-studio scene or something, would be to use the 1-10000 slider for a brighter light.
The fire primitive will also act as a light emitter with Indirect Light as well. It creates some weird effects though.
Excellent! So there you have that too! Thanks ep!