Advanced lighting and rendering

1. Advanced lighting and rendering Multipass rendering

2. Outline • Introduction • What is it? • Advantages and disadvantages • Multipass rendering in Maya • Some examples

3. Introduction • Previously we have looked at many different types of lighting and rendering • These can produce highly realistic results • There are occasions when we need special effects or more subtle control over what we produce • This lecture looks at one technique for this: multipass rendering

4. Multipass rendering • When we render a scene, there are many components that combine to produce the final rendered image • Multiple light sources • Multiple objects (each of which may reflect light back into the scene) • Each surface has multiple components (diffuse, specular, reflective, etc.) • There will often be occasions when you need to alter one or more of these components after the render • This will normally require re-rendering the entire scene • We can avoid this is with multipass rendering

5. Multipass rendering • Basically this involves rendering one or more components of the pixel values that make up your finished image to separate images • These images can then be combined to make a single image using compositing techniques (e.g. in Photoshop for a still or After Effects for a video) • By changing the way in which these components are combined we can alter their effect on the final image without re-rendering the entire scene • For complex scenes this can save a lot of time

6. Simple example • Consider a scene with classic 3-point lighting (key, fill and rim) • We can render the effect of each of these lights to separate images • We can then combine these to give the desire value to each light

7. More advanced MP rendering • So far we have just changed light parameters to create our multipass renders • There is more we can do to add even greater control by adjusting surface parameters and render options • Consider an example…

9. Types of passes • Typically there are a number of passes that will be used: • Beauty pass • Diffuse pass • Highlight (or specular) pass • Reflection pass • Shadow pass • You may use some or multiple versions of each pass in the finished result

10. Summary • Introduced multipass rendering • Discussed why it’s useful • Looked at some examples