Rendering is the act of converting the scene information into a bitmap image by evaluating all the geometry and lighting information in a given file. Generally users will expect the resulting rendered image to be a fully ray traced and shaded image with full shadows, reflection and the like, much like a photograph depicts an entire scene when taking a picture with a camera. In MODO these images are the result of what are called "Render Outputs", the visible representations of the full scene evaluations. Each Render Output is a separate layer in the Shader Tree and will produce its own image layer as part of the render calculations. Every time a Render command is invoked, all of the render output layers are simultaneously calculated and represented in the Render Display viewport. The different layers can be viewed by choosing one of the specific 'Output' options within the display window.
Occasionally users will only want a subset of the full evaluations, such as the diffuse color layers without any shadows. MODO offers many different 'Render Output' types useful in a variety of situations ranging from purely diagnostic, to specific compositing utility in an external application. A default scene automatically includes a 'Final Color' and 'Alpha' output which should be fine for most situations. Additional layers can be added from within the shader tree viewport itself, by LMB-clicking the 'Add Layer' option of the full viewport window and selecting "Special >> Render Output" from the pop-up menu. This adds an additional layer to the top of the tree. Users may then RMB-click in the 'Effect' column of the Render Output for a pop-up context menu that allows one to select from the alternate output types. Please reference the primary Render Outputs page of the documentation listed under the Shader Tree Layers section for for information regarding the editable attributes of the individual outputs. Examples of the various output types available are as follows--
Ambient Occlusion
The 'Ambient Occlusion' output generates an occlusion image where occluded areas; crevices and other inaccessible areas of a scene shade darker, while open areas render lighter colors, approximating an overall global illumination type of shading. Grainy renders can be smoothed out by increasing the 'Occlusion Rays' value, controlling the density of the occluded areas is done through the 'Occlusion Range'. Reference the 'Ambient Occlusion' section on the secondary Render Output page for more information.
IC Positions
The settings within the 'Render Item > Properties > Global Illumination' tab allow you to specify values that the Irradiance Cache uses to shade a rendered scene. The 'IC Positions' output will display the pixel positions used in generating the shading based on the Irradiance Cache values. Green points are positions sampled during the initial pass, Red points signify additional sample generated by the Interpolation Values setting. Useful in analyzing various IC settings.
IC Values
The settings within the Render Item > Properties > Global Illumination Tab allow you to specify values that the Irradiance Cache uses to shade a rendered scene. The 'IC Values' output will display the diffuse values calculated during the initial irradiance cache render pass. The image will appear splotchy as each irradiance sample is not blended with nearby samples; giving one a much better understanding of the area affected by individual IC positions. Useful in analyzing various IC settings.
Illumination (Direct)
The 'Illumination (Direct)' output generates a channel exclusive to the illumination in a scene from all direct light items such as distant lights, area lights, point lights and spot lights, independent of all other illumination types and surfacing attributes.
Illumination (Indirect)
The 'Illumination (Indirect)' output generates an image exclusive to the illumination in a scene from all indirect sources such as image based lighting and luminous polygons, independent of all other illumination types and surfacing attributes.
Illumination (Total)
The 'Illumination (Total)' output generates an image of the full illumination evaluation in a scene, including shadows cast by direct sources, but independent of all other surfacing attributes.
Illumination (Unshadowed)
The 'Illumination (Unshadowed)' output generates a channel of the full illumination in a scene excluding shadows cast by direct light sources, independent of all other surfacing attributes.
Reflection Occlusion
The 'Reflection Occlusion' output renders an image that is strictly black and white, determining if a reflection ray off of an object has hit any other geometry in the scene. White if it has and black if it has not. The areas that appear as white here would be shaded with the background environment in a Final Color render.
Shadow Density
The 'Shadow Density' rendering output renders a channel generated from the density of all direct light shadows in MODO exclusive of color shading or texture. The darkest areas of shadow render as white white ramping toward black for the areas that would be fully illuminated. When rendering in layers, it is very useful to have shadows rendered separately giving one control of color and transparency. You could easily invert this channel in an image editing application and layer it over the unshadowed render set to 'multiply', giving control over how dark the shadows are based on the layers transparency.
Render output are incredibly useful when users wish to compose the generated layers individually in an external application, such as Photoshop, After Effects, Nuke or Fusion. This can aid in tweaking color, among other settings as a post process without requiring additional render time. The question most often asked is "Which Render Outputs combine to equal the Final Color output?" The answer is "Diffuse Shading (Total) + Transparent Shading + Reflection Shading + Specular Shading + Subsurface Shading + Luminous Shading = Final Color", where each successive layer is added to the layer below in the composition (also called Linear Dodge). Rendering each layer at a gamma of 1.0 and then combining them and adding the gamma back to the fully composed layers will produce the best results.
Users may also render out simultaneous alpha channels for each item in a scene by creating item masks for each and placing a render output set to Effect > Alpha (or simply adding them to existing Shader Tree masks). Then each time a render command is invoked, all active (visible) render outputs will be generated simultaneously.
