Logikoma with simple outlines from "surface color" AOV (image credit: Paolo Berto Durante)
Outlining are typically used to define silhouettes and to outline features when doing toon/anime rendering or illustrations.
Outlines are often combined to CEL/toon shading, a type of non-photorealistic shading designed to make 3D computer graphics appear to be more "flat", for example in Maya the "Ramp Shader" offer this kind of look. However there are no artistic restrictions and outlines can also be combined with PBR-style rendering to develop more hybrid, photo-surreal and artistic looks
3Delight for Maya can perform outlining on any number of any desired Image Layers, including:
- shading component AOVs
- auxiliary AOVs
- "multi-matte" mask AOVs
- custom AOVs (any shading variable can be used for outline detection when output as a shading output)
Advantages of using the 3Delight outlining system:
- Powerful imagelayer-based decoupling of the detection phase and the drawing phase
- Easy to setup
- Ultra high quality outlines, due to state of the art sub-pixel anti-aliasing and filtering
- Fully working both in interactive IPR and final frame rendering
- Outlines are drawn immediately (no need to wait for the end of the frame)
- Strong outline animation stability
- Supported in both Path Tracing (default, higher quality) and REYES (faster, lower quality)
An example scene can be found at this location inside your 3Delight installation: $DELIGHT/example/maya/outlines.
The Outlining subgroup
Draw Outlines in this Layer
This attribute enables drawing of outlines for the selected layer. This can be seen as an indicator of which layer receives the outline. It is set to off by default with the exception of the "outline" AOV which receives outlines by default.
Generate Outlines Using this Layer
This attribute enables outline generation using the specified layer. Good image layers for detection purposes are the ones with sharp color discontinuities which facilitate the detection algorithm. When multiple image layers are used for generation (detection), they will be combined and drawn together according to depth informations.
Usually (a combination of) the following auxiliary image layers, available in the AOV Selector, are used to generate outlines:
- surface color (auxiliary): this is the un-shaded and un-illuminated (textured) color of any object. It offers good stability, detection will act between colors and on any texturing color which will be present in the image layer, this means you can use ad-hoc textures to trigger detection of any detail you might want
- geometry ID (auxiliary): the unique color-coded geometry ID (supports also instances). It offers goods stability, and will detect an outilne between different object/instances
- shader ID (auxiliary): the unique color-coded shader/material ID. It offers goods stability, and will detect an outilne between different materials
- depth (auxiliary): this image layer is less stable, being view-dependent. An outline will be detected between regions at different depth
- camera space normal (auxiliary): this image layer is less stable, being view-dependent. An outline will be detected between regions where surface normal face away
- any geometry/material 3delightMaskSet (masks): being black and white masks offer perfect contrast for detection
- any additional custom AOV you might need
There is a wide range of artistic possibilities as any number of AOVs (including masks, auxiliary and custom ones) can be used to detect outlines, regardless of how stable they are it is up to you and your artistic purposes to define the look.
When this toggle is enabled, a part of the UI becomes sensitive to set the parameters of the outlines.
Outline parameters become sensitive for layers generating the outline.
Color
Specifies the color of the generated outline. It is set to white by default.
Outline Width
Specifies the width of the generated outline. It is set to ‘0.2’ by default. Values between ‘0’ and ‘1’ are allowed, producing very fine outlines. In this case it is recommended to raise the Pixel Samples attribute (in the Quality group or rendering attributes) in order to avoid aliasing of the outlines. Next to this attribute, there is an option menu to determine how this width should be interpreted. The available options are:
Option | Description |
|---|---|
| Pixels | The filter width is a number of pixels. |
| % of Frame Width | The filter width is taken as a percentage of the image resolution in X. |
Threshold
Specifies the sensitivity of the outlining. The higher the threshold the more sensitive is the edge detection. For example, when detecting variations on ‘z’ (depth), a value of ‘0.1’ means that if there is a gap of ‘0.1’ between two surfaces (in the z direction) then an outline will be generated. This attribute is set to ‘0.1’ by default.
Depth Based Fadeout
Specifies the edge thickness fadeout with depth. It is off by default.
Min Z
Max Z
These two attributes specify the depth range on which the fadeout will be performed. By default, "Min Z" is set to ‘0.0’ and ‘Max Z’ is set to ‘1000.0’.
Min Filter Width
The depth based fadeout will keep outlines with a minimum width specified by this attribute. Its default value is ‘1.0’.
Note that you can override the color and the width scale (thickness) of outlines on a shader-basis, by tweaking the relative attributes in any Maya ShadingGroup nodes: both accept texture mapping with any Maya shading node/network, and will use the UVs coordinates inherited by the geometry to which the surface shader is applied.