Advanced lighting and rendering Multipass rendering

Outline  Introduction  What is it?  Advantages and disadvantages  Multipass rendering in Maya  Some examples

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

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

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

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

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…

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

Summary  Introduced multipass rendering  Discussed why it’s useful  Looked at some examples