Intro to Materials and Lighting with Andrew Klein

BACK TO TEACHING HOMEPAGE BACK TO COURSE HOMEPAGE

GA 3311: Materials and Lighting In this class students will be introduced to materials, textures and lighting strategies to add detail and realism to objects without adding complexity to the model. Students will simulate real world surfaces containing reflection radiosity and other effects.

JUMP TO A SPECIFIC WEEK:

week 1, week 2, week 3, week 4, week 5, week 6, week 7, week 8, week 9, week 10, week 11

Week 6: The Render Settings Window (aka Render Globals):

********LIGHTING AND RENDERING WIKI, CLICK HERE*********

Common Render Attributes:

File Name-This function sets the name of your image file after the render. in the file to the left, it will be awesome_car
Frame/Animation Ext-This sets the output extension for each of your frames. Use name.ext to save our awesome_car.jpg; a single frame. Use name.#.ext if you are rendering out a sequence of images. Use name.ext.# if you want your images to be readable as an animated texture.
Image Format-This sets the type of image: jpg, gif, tiff, iff, targa, etc...
Start Frame-the starting frame of animation you wish to render.
End Frame - the final frame you wish to render
By Frame -usually set to 1, is the interval of frames to render by. Set to <1 for ultra fast speeds, set to >1 for stop motion like effects or lower quality of framerate.
Frame Padding-sets leading zeros on your frames. If was rendering out frames 1-900, my frame padding would be 3, so that I would count 001, 002, 003...010, instead of: 1, 10, 11...19, 2, 20, etc....
Renderable Objects-All or Active are the two choices, usually leave at render all.
Camera-Chooses which camera to render from.
Resolution-pixel width by height for the render.
Aspect Ratio-Sets the ratio of width/height. 4:3 is the default value (listed as 1.333), 16:9 or 16:10 are two common widescreen values.

Maya's native Renderers:

Maya Harware Renderer-
Generally the fastest rendering option in maya, the hardware renderer creates bitmap images by utilizing the graphics card. While fast, the images tend to lack depth and realism as certain effects like shadows, reflections, refractions, as well as come particle types cannot be rendered without baking into the texture first.

Maya Software Renderer-
The default renderer for Maya, the software renderer creates bitmap images by utilizing the processor(s). Can caculate textures, reflections, refractions, blur, all particle types and lights. However it is slow compared to more advanced renderers, and slows considerbly with the addition of extra lights. Cannot compute GI, FG, or Caustics.

Maya's Plug-in Renderers:

Maya Vector Renderer-
While the Vector Renderer was designed for .swf (flash) output, it is also an effective renderer for toonshaders, as well as for producing crisp wireframes for modeling turtables. You can specify edge size, fill color, levels, and other features common to adobe illustrator paths, or posterize filters in photoshop. Matt Higison's Wireframe Tut., click here.

Mental Ray for Maya Renderer-
A default product shipped with maya since version 5, mental ray is generally a faster software type renderer than the actual maya sofware renderer, as well as physically more acurate. Can compute all effects that Maya Software is capable of, but also can render Global Illumination (GI), Final Gather color bleeds (FG), and Caustic effects/highlights. While not as adept with lights as Renderman for Maya, can handle more lighting effects in general without the same ammount of slowdown as Maya Software will experience.

We should note that these are not the only renderers available as well. Other 3d packages share Mental Ray and Renderman and can also use their own native renderers or different 3rd parties such as Brazil or VRay.

Reflections: Raytracing your scene-
To be able to produce reflections in your scene, or to render with raytraced shadows, we must enable raytracing in our render settings window. From the Wikipedia: "It works by tracing, in reverse, a path that could have been taken by a ray of light which would intersect the imaginary camera lens. As the scene is traversed by following in reverse the path of a very large number of such rays, visual information on the appearance of the scene is built up as viewed from the point of view of the camera. The ray's reflection, refraction, or absorption are calculated when it intersects objects and media in the scene. ...In nature, a light source emits a ray of light which travels, eventually, to a surface that interrupts its progress. One can think of this "ray" as a stream of photons traveling along the same path. In a perfect vacuum this ray will be a straight line. In reality, any combination of three things might happen with this light ray: absorption, reflection, and refraction. A surface may reflect all or part of the light ray, in one or more directions. It might also absorb part of the light ray, resulting in a loss of intensity of the reflected and/or refracted light. If the surface has any transparent or translucent properties, it refracts a portion of the light beam into itself in a different direction while absorbing some (or all) of the spectrum (and possibly altering the color). Between absorption, reflection, and refraction, all of the incoming light must be accounted for, and no more. A surface cannot, for instance, reflect 66% of an incoming light ray, and refract 50%, since the two would add up to be 116%. From here, the reflected and/or refracted rays may strike other surfaces, where their absorptive, refractive, and reflective properties are again calculated based on the incoming rays. Some of these rays travel in such a way that they hit our eye, causing us to see the scene and so contribute to the final rendered image."

Global Illumination and Final Gather

Global Illumination-
As we previously mentioned, Light can exhbit the ability to reflect off a surface. The more luminous the surface (the whiter the surface), the more light will be reflected. Since light is reflected off of all materials (see Dif.-Gloss-Spec.-Refl. above), we should assume that when multiple objects of a luminence greater than pure black (ie, everything except for black holes) are present in our scene, that light will reflect back into the shadow areas on nearby objects from that surface. This principle is used in Hollywood on sets by having stagehands hold up brightly colored reflectors when filming in directional light to make shadows on actors face's seem softer (see image below).

As we set up global illumination, we need to observe the how the light bounce will effect the shadow areas. In the demo below, The light rays emitted from our source (spot light) will bounce off of the ground plane and onto the shadow side of ball, thus lightening the shadow.

To render global illumination:

First, make sure at least one light source in your scene emits photons
Select the Rendering menu set.
Open the Render Global Settings window.
Click the Select Window > Rendering Editors > Render Globals or click the Render Global Settings window icon.
Select the mental ray for Maya render.
Click the mental ray tab.
From the Quality Presets drop-down list, select PreviewGlobalIllum.
Raytracing and global illumination (in the Caustics and Global illumination section of the tab) are automatically enabled.
Render with the default settings.
If the default settings are not sufficient to achieve the look you want (or to reduce render speed), tweak the global illumination settings until you achieve the look you want.

Final Gather-
Final gather is method of simulating global illumination. When used in combination with global illumination, Final Gather lets you create the most realistic, physically accurate lighting conditions for a scene (using Global Illumination alone can sometimes give splotchy results).

When Final Gather is enabled, every object effectively becomes a source of ray-emitting light, mimicking the natural world in which objects influence the color of their surroundings. When one light ray strikes an object, a series of secondary rays are diverted at random angles around it to calculate the light energy contribution from the surrounding objects. The light energy is then evaluated during the ray tracing process to add the effect of the bounced light.
Unlike Global Illumination, Final gather does not use photon maps to calculation of light at a given point in scene. Instead, mental ray for Maya samples the surrounding area above every point in the scene. The illumination at those points is then computed as direct illumination. (If Global illumination is also being used at the same time, Final Gather calculates the total incoming illumination in the scene [called irradiance].)
Final Gather rays are emitted in many directions from a sample point and stop according to the settings in the Final Gather section of the Render Globals Setting window. Because Final Gather rays do not bounce, secondary surfaces are not taken into consideration. (However, when rays hit geometry, material shaders may cast secondary reflection, refraction, or transparency rays, as long as those secondary rays are specular or glossy, not diffuse.)
Final gathering eliminates the low-frequency variation in the global illumination that often results if too few photons are used. (Performance is optimized because mental ray for Maya reuses and interpolates nearby final gathers.)

Final Gather and Global Illumination- Tag Team back again, check and direct and let's begin:
You can combine Final Gather and Global Illumination techniques to:
-achieve realistic lighting and shadows more cost effectively
-reduce flicker in animations
-effectively illuminate interiors (global Illumination on its own can sometimes render splotchy results)
-You can reduce the number of Global Illum Photons, the Global Illum Energy levels, and the number of Final Gather Rays resulting in less rendering time, but more realistic lighting.

To render with Final Gather-

First, turn off Maya default lights (see Turn default lighting on or off) and, if you have any light sources in the scene, turn off their Illuminates by Default attribute.
Select the Rendering menu set.
Open the Render Global Settings window.
Click the Select Window > Rendering Editors > Render Globals or click the Render Global Settings window icon.
Select the mental ray for Maya render.
Click the mental ray tab.
From the Quality Preset drop-down list, select PreviewFinalGather.
Final Gather (in the Final Gather section of the tab) is automatically enabled.
Change any of the following optional settings, which can have an effect:

- The camera background color.
-The object's material's colored Incandescence or Ambient color attributes.
-Irradiance contributions from shaders.
-Irradiance color mapping contributions from shaders.
-The number and location of lights in the scene.
Render with the default settings.
If the default settings are not sufficient to achieve the look you want (or to reduce render speed), tweak the Final Gather settings until you achieve the look you want.

Caustics

Caustics are light patterns that are created when light from a light source illuminates a diffuse surface via one or more specular reflections or transmissions. Examples are:

The light patterns created on the bottom of a swimming pool as light is refracted by the water surface and reflected by the diffuse pool bottom.
Light being focused by a glass of water onto a diffuse table cloth.
The light emanating from the headlights of a car: the light is emitted by the filament of a light bulb, reflected by a parabolic mirror reflector (thereby being focused in the forward direction), and reflected by the diffuse road surface.

Homework: Build your own cornell box and produce two renders. In one, use mental ray for maya to render out the effects of global illumination and final gather to produce softened shadows and color bleeds. In the second render, use maya's vector renderer to produce wireframes. These are due week 7. Additionally: Please go back to your fruitbowl project and render out the scene again with GI and FG activated. Turn in one of those renders in week 7 as well.

Examples of Student Work:

Image by Tamar Yacoubian	Image by Takumi Kobayashi	Image by Jonathan Price
Image by Dacotah Turner

JUMP TO A SPECIFIC WEEK:

week 1, week 2, week 3, week 4, week 5, week 6, week 7, week 8, week 9, week 10, week 11

	Maya Harware Renderer- Generally the fastest rendering option in maya, the hardware renderer creates bitmap images by utilizing the graphics card. While fast, the images tend to lack depth and realism as certain effects like shadows, reflections, refractions, as well as come particle types cannot be rendered without baking into the texture first.
	Maya Software Renderer- The default renderer for Maya, the software renderer creates bitmap images by utilizing the processor(s). Can caculate textures, reflections, refractions, blur, all particle types and lights. However it is slow compared to more advanced renderers, and slows considerbly with the addition of extra lights. Cannot compute GI, FG, or Caustics.