what does global illumination do? getting the best renders out of it?
Mistara
Posts: 38,675
i understand idl a bit, but never really understood why it isn't the same as a high number of raytrace bounces?
global illumination is even better than idl? are they co-dependent?
hoping to learn gi for the #16 challenge :)
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IDL?
Global Illumination is as close to real world lighting a biased renderer can get.
In extremely simplistic terms:
Standard ray tracing doesn't calculate light reflecting off an object and hitting another object, and reflecting off that object, etc. It traces the photon's path from the camera to the object only.
Full GI calculates the ray's interaction with the vase it hits, and then when the ray reflects off the vase, it calculates where it hits next, the color and reflectivity of the material reflecting the ray, etc. etc. That's why light calculations take so long.
Skylight is a component of Carrara's GI, but it is not full GI. Carrara's Skylight system allows you to mimic 360º atmospheric light with the Realistic Sky, or an HDRI, image map, color or color gradient in the scene's Background slot. Using an HDRI as an example, the light comes from all directions, with the brightest areas of the HDRI generating more light, and darker areas of the HDRI producing less light, the color of the light will be driven by the color in that particular area of the image.
The Skylight looks close to GI due to the fact that it is coming in from all directions, but unlike full Indirect Light, it doesn't reflect off one object to illuminate an object next to it. When using an HDRI or an image map as a light source a common acronym is IBL, which stands for Image Based Light.
In these two samples, I use Indirect light. The lamp is the only light. I used different colored materials to show what effect it has when they are changed.
When we get into the next challenge, I can offer some tips to speed up a GI render that are really cool. Others will undoubtedly have some as well.
is gi for outdoor scenes only?
a light study prolly be more time economical if i learn how to use batch rendering :lol: let it all run when i'm sleeping
No. GI is a kind of a generic term. If you look at Indirect Lighting and Skylight in Carrara, they are both in the Global Illumination (GI) field, below the standard renderer's options.
The Skylight option allows you to use IBL (Image Based Lighting). The Skylight option isn't full GI, because it doesn't reflect light off of objects and onto other objects. It is most effective for outdoor shots or when you use an HDRI.
Indirect Light is considered full GI. It works best for indoor scenes, as light hits an object, such as a wall and reflects light off of it, and onto the vase on the floor next to the wall.
You can use Skylight and Indirect Light together, but beware of doing so in outdoor scenes, as if you have trees, Carrara will calculate the light bounces off of all those leaves!
Tell me about it! I found that out the hard way!!!
Another example of indirect light. There is only one light in the scene (a bulb light). The only difference between the two images is the use of indirect light. To give better indirect illumination I enclosed the scene in a cylinder to provide something for the light to reflect (bounce) off of, and a simple plane primitive used as a reflector as would be done in a photo studio. Ambient light is also set to 0 for both renders.
Indirect light is a lot slower to render, but I usually prefer the results.
I'm so glad you ask questions, Misty. I saw your mention of GI in another forum and wondered what it was. My lack of knowledge far outweighs my knowledge. Why aren't there more non-sleep hours in a day?
This shows the basic scene setup for the above images.
I think this example shows a bit more dramatic difference between the image using GI/IDL and the one that doesn't. Again, the only difference in the two images is that I enabled indirect light in one and not the other. Simply put, IDL just enables light bounced/reflected from the light sources off of other surfaces in the scene to illuminate portions of the scene that aren't directly illuminated by the lights.
"Faked GI" is a method where many additional low intensity lights are added to give the appearance of bounced light in the scene (Faked GI is typically faster because it requires fewer calculations per light source).
I'm beginning to see the light. Now to play with some scenes and lights.
it is abysmally slow to render
unless one figure with a shadowcatch plane and only skylight not indirect light.
Faked GI can still be pretty slow - in the outdoor scenes I've posted on the render thread (lots of trees & plants), it's the difference between a 2.5 hour render and a 4.5 hour render for "Skylight" GI
another good reason to learn how to use batchq. leave these rendering o/n. :)