...
- Allow for additive compositing, preserving the physical nature of the image and avoiding artifacts through multiplication or division in post processing.
- Output a specific bounce of light (2nd, 3rd, etc.) or even a range of bounces (4th to 8th bounce of light). You can use this to isolate effects or even noisy bounces for subtraction.
- Output a specific object to an LPE. While you can use Cryptomatte to isolate objects with an ID, you can also output the object or collection of objects and their contribution separately.
- Isolate a particular noisy light path for subtraction in comp or an LPE without these light paths to composite.
- Create a non-physical effect like differently colored caustics from their source, change the color cast of an object, or scale lighting.
- Output per-light AOVs for manipulation later.
| Note |
|---|
Note that trace sets can also be used to accomplish some of these effects but since trace sets are global in the render, LPE will obey these trace sets (meaning data that would have been collected otherwise is restricted by the trace set). Light Path Expressions handle light transport, as such they collect illumination by default and not shadows (shadows are simply a lack of light) A specialized Shadow LPE is provided for compositing tasks as part of our Holdout workflow. Since these follow the physics of light, your LPE will use addition (plus) and subtraction (minus) as adjustments in compositing. This avoids artifacts introduced by multiplication and division that should happen at the sample level, not on final pixels. |
...
Above we use the most common ways to collect light paths, you either want all, direct, or indirect. This handles most scenarios you come across. But there may be reason to do something with a specific bounce or set of bounces. This can be anything from non-physical scaling of the light (brighter or darker) or isolating a specific bounce where noise is introduced and subtracting it from the final result. This last example is best when you can isolate the object(s) causing the noise. This will be covered under LPE Groups. Below is an example of rendering only the first (direct light), secon, and third light bounce. These LPE are all very similar to the Beauty LPE but we exchange the * for all bounces with a specific bounce contained in a curly bracket {} For example, {1} collects the first bounce or the direct light frm the ceiling rect light to the object and then immediately to the camera. The second bounce is {2} which says the light must interact with something one more time before being stored, this is the first indirect bounce after light meets a surface. This goes on until the path length is terminated by the parameters in the Render Settings, Max Specular/Diffuse depth and/or Max Path Length for the integrator and possibly russian roulette (all the energy was already absorbed leaving you with no more information to store).
| Code Block |
|---|
lpe:C<[RT][DS]>{1}[LO]
lpe:C<[RT][DS]>{2}[LO]
lpe:C<[RT][DS]>{3}[LO] |
| Carousel Image Slider | ||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
...