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<  Iluminação  ~  Global Illumination: interiors

Colocada: Ter Jun 20, 2006 8:55 pm Responder com Citação
Veterano Registo: 31 Jan 2005 Mensagens: 1402 Local/Origem: inbicta
V-Ray Lighting Techniques with Christopher Nichols

1. Key elements from the Exteriors Lighting scenes
- Light reflects in space and scatters light.
- Diffuse light scatters light differently from specular light.
- The rougher the surface the more specular light scatters.
- There are different methods for scattering diffuse light.
- Radiosity is a very solid method for interiors because of the way that it can bounce light around.
- Photon mapping is also good for bouncing light around very efficiently, but can be problematic for
environment lighting.
- QMC system gives the highest quality but is the slowest overall method.
- Irradiance mapping is only good for the primary bounce, as it is an optimized method of collecting
light samples. Note that it is only useful for the first bounce.
- Environment light can be achieved by several methods. Image based lighting using HDRI is one of the
most common and is also one of the best methods.
- Animation techniques that were discussed on the Exterior GI lighting DVD are still very valid for
lighting static scenes.

2. Interior versus Exterior GI
- Exterior scenes are usually simple lighting scenes as they usually deal with single light sources such as the
sun and the sky.
- Interior scenes have more complex lighting as the geometry itself reflects light, and the geometry
becomes an environmental light source. Interior scenes can have many types of light sources.
- Light needs to bounce off of many more surfaces compared to exterior scenes.
- Special optimization techniques need to be used to make the renderings more efficient.
- With exterior GI lighting, we need to learn to set up scenes so that they light themselves naturally.
- In interior scenes we need to learn to light in the same way that a photographer or cinematographer
would light a scene.

3. Lighting Interiors with Exterior Light
- When lighting interior scenes through an exterior environment, it will require us to use a high intensity
multiplier on the environment to compensate for the darkness of the space.
- We also need to bounce light around more to get better light coverage.
- While HDRIs do not affect the scene’s lighting as dramatically as they do with exterior scenes, they still
provide a subtle difference to help the variation of lighting as opposed to simply using a solid
color for the environment.
- Affecting the color of elements in the scene affects the overall color of the lighting.
- Elements that are receiving more direct light (such as a floor) affect the scene more than objects that
receive less light (such as the ceiling).
- On reflective (specular) surfaces, darker surfaces appear more reflective than lighter surfaces.
- Specular reflections need to be broken up through textures in several spots – through reflective intensity,
and through roughness (or glossiness).

4. Other Interior Light Sources
- When building interior lighting scenes, it is important to build them to scale especially when using light
sources, which all have to be scaled to the scene.
- Light sources have an inverse square decay.
Understanding color space:
- Renderings are calculated and displayed in linear color space, while your monitor needs to be gamma corrected.
- There are several ways to compensate for this.
- The best way is to keep your image saved in linear color space and adjust your Virtual Frame Buffer
(VFB) to display the image with a gamma correction.
- The other way is to “burn” the gamma curve into the image using the color mapping method.
- For a PC, the gamma is usually a 2.2 gamma. If you choose to use the color mapping method inside of V-ray,
use Gamma Correction at a value of 0.4545 (which is 1/2.2).
- V-ray area lights have an inverse square decay and vary in intensity based on their size.
- IES lights are a specialty light type that reads a lighting file by the lighting manufacturer that describes the
light with a 3 dimensional plot of how the light intensity is distributed from the light source.
- Lighting manufacturers generally freely distribute IES files over the internet.
- Look for lighting companies on the internet such as Lithonia and Erco.
- There are many free IES file viewers that can be found on the Internet to help pick light sources by
giving a visual representation. Do an Internet search on IES Viewer to find them. The one I enjoy
using is the one written by Tony V. Morev.
- Using IES lights can greatly increase your lighting library.
- IES lighting can be slower in V-ray due to the complexity of the falloff of the light sources.
- Objects can also be made into light sources in V-ray, but are only viewable in diffuse when using GI.

5. Lots of Secondary Bounces
- In order to efficiently get a lot more bounces in our scene, we need to use alternate methods of
bouncing secondary bounces other then QMC.
- Two methods can be used in V-ray: Photon mapping and Light Caching.
- Photon mapping shoots a fixed amount of samples of light and bounces them around a scene collecting
light colors and intensity.
- Photon mapping is very efficient at bouncing those samples around many times but is not very good at
giving very clean results.
- The trick to using photon mapping is balancing how V-ray averages neighboring samples.
- Photon maps can only be used on a certain types of light sources: V-ray lights, spotlights with an
inverse square decay starting at one unit away, and direct light sources. It cannot be used for light
sources like omnis, skylights, IES light sources, and others.
- Photon map data can be stored with the irradiance map data to reduce the amount of data (and time)
needed for the irradiance map.
- Light cache operates differently as it is view dependent.
- One big advantage about light cache is that it has essentially infinite light bounces.
- Any light source can be used with light cache.
- The disadvantage (over photon mapping) is that it may miss a very small (but bright) light source
far away, such as a laser.
- Keep in mind that photon mapping is still a very useful method of calculating Caustics. In V-ray, Caustics
are calculated separately from photon mapping, but both methods shoot rays similarly.
- Light Cache calculation can also be used to accelerate glossy ray effects.

6. Baki ng Lighting into Textures
- V-ray does have an ability (all be it a limited one) to take advantage of the 3dsmax texture baking capability.
- In order to use it most efficiently, a combination of sample baking with texture baking is needed.
- If one used the straight texture baking, you can risk light leaks and collecting unneeded samples.
- You will also have to bake each object individually to collect all the correct g-buffer data.
- Pre-baking an irradiance map and a light cache or photon map can be very useful.
- Since irradiance maps and light cache samples are view dependent, an easier way to collect samples
for a space is to use the V-ray spherical camera and placing it in key locations using a camera path.
- If some light leaks still happen, remember that the lighting is saved as a texture file so a regular 2D paint
program, such as Adobe Photoshop®, can be used to paint out the light leaks.
- Baking the lighting into textures will only bake out the diffuse light. Specular light still needs to be done
in the regular way.
- Baking lighting into textures with V-ray is not as efficient or as good a quality as doing it with sample
baking, but can be useful for game and other interactive scene creation.

7. Lighting Scenario 1
- When doing a complex scene, several steps can be used to work your way through the lighting process
more efficiently.
- The first step is to use a simple gray shader to get an idea of what the lighting is doing without the
influence of shaders or textures.
- When you first place the major key and fill lights use the light cache for the primary and secondary
bounces to do lighting studies. The results will be poor quality renders, but will give very quick feedback
as to the light conditions and general effect of the global illumination.
- Use small samples and subdivisions on things such as V-ray shadows, glossy effects (as you start to use
those features) only increasing them for the final render.
- Before painting textures, it may be helpful to create shaders with solid colors that approximate the
desired colors for major elements in the scene. This should be done for things like floors and walls
since they will influence the GI the most.
- Dial in the color of the shaders and use those colors as the base for the textures.
- Remember to look at your shaders in both gamma corrected space and linear space within the material editor.
- Paint all texture in linear space.
- The important maps to consider are color, specular, glossiness and bump.
- If using transparency, remember that raytracers can take advantage of color in opacity as well.
- When dealing with more complex lighting, it is always a good idea to turn on major feature lights and fills
one at a time to see how they affect the scene and to dial in their colors and values.
- Lighting with GI is closer to lighting as a photographer or cinematographer.
- It is useful to create light kits that are similar to those used on set. Using IES lights, barn doors, even flags
and bounce cards can be very useful.
- Playing with the exposure and the gamma curve inside the VFB can help guide us to figure out if we
need to brighten or darken the scene, as well as adjust the key to fill ratio.
- The global illumination data can be manipulated in V-ray to affect brightness, contrast and saturation.
This is an easy way to control the “fill” in you scene, even if it is not as physically accurate.


Helder "hP" Pinto

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Colocada: Qua Jun 21, 2006 10:11 am Responder com Citação
Site Admin Registo: 28 Jan 2005 Mensagens: 1539
Acho que já vi isso em algum lado.. hehe... muito bom em partilhares. thanks Very Happy
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Colocada: Sáb Fev 20, 2010 1:35 pm Responder com Citação
Registo: 20 Fev 2010 Mensagens: 3
Custam mais de 5 vezes que as equivalentes nas lojas chinesas e duram o mesmo tempo ou até menos!
A direcção da OSRAM disse que as deles tinham garantia
Estranhamente trocaram-me na realidade as duas guias de remessa n 7581 de 15-04-08 e a guia n 7826 de 18-03-09.
A última foi remetida, fundida à direcção da OSRAM em 23-10-09.
Perante o silêncio da OSRAM, escrevi à direcção uma carta em 14-12-09
É um espanto, até agora nada, nem lâmpada nova veio, nem tão pouco resposta à minha carta de então!
Instaladores e consumidores: OSRAM NUNCA MAIS.
Actualmente se não são fabricadas na china são em sitio muito semelhante; sem a qualidade de outrora.
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