Pipeline Render Passes

Tips & Tricks      Pipeline Techniques      Level: Intermediate     Date: 11th June 2008 

Pipeline Techniques : Render Passes The term Render Pass has often been used interchangeably with Render Layers When rendering in layers each layer is assigned what objects are to be in it. That is to say, the main character or the static objects or background objects. More often, inside Maya it is used to override renderers. Example: render one layer having objects to be rendered using Mental Ray and another layer to render paint effects using the Maya Software Render. There can be many such combinations. In a production pipeline, the more important part of the “layers” was to have different features (object properties) of the render elements, so that these may be composited in the way one desires at the time of compositing. This allows for a great deal of flexibility at the time of compositing.

The most common features of a rendered object or scene is 1) 2) 3) 4)

The look of the object (color, texture, etc) Shadow of the objects Environment / Background Effects

 

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Tips & Tricks      Pipeline Techniques      Level: Intermediate     Date: 11th June 2008 

Sharks

Blood

Cage

 

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Tips & Tricks      Pipeline Techniques      Level: Intermediate     Date: 11th June 2008 

Fog & Light Rays All these layers need different type of renders, as the layer for Blood, being hardware particles had to get rendered using Maya Hardware. There could also be a case where there are Paint Effects which specifically need to use the Maya Software Render. All the above images can then be composited to get the final image:

Based on the above, The look of the object includes the diffuse, specular, reflection and others. Sometimes these features when merged inside the software as the rendered image, do not necessarily give the look desired by the artists. Hence, they are often rendered separately.

 

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Tips & Tricks      Pipeline Techniques      Level: Intermediate     Date: 11th June 2008 

1) Diffuse Pass (Beauty pass or color pass) :

The is the main pass as the main object look (color and texture) is in it 2) Specular Pass : This pass has all highlights. 3) Depth Map Pass:

the distance of objects from the camera  

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Tips & Tricks      Pipeline Techniques      Level: Intermediate     Date: 11th June 2008 

4) 5) 6) 7)

Effects Pass: The glows, rays etc… Reflection Pass: Reflection from surrounding environments and objects. Shadow Pass: Ambient Occlusion Pass:

Increase contrast of the objects as well as their relation to other objects 8) Normal Pass:

Explained in accompanied tutorial The above is not a complete list, but indicative of the commonly used layers. It is not compulsory that the scene “HAS TO” be broken up into the above set layers. As such there could be an “object pass” that has diffuse, specular and reflection. Sometimes the simple geometry mask or even the alpha of the main object can be useful. For example, if we need a glint (shine/shimmer) on the contour of the object, we can use it’s alpha (slightly increased and/or offsetted) and then have that to glow/shine.

 

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Tips & Tricks      Pipeline Techniques      Level: Intermediate     Date: 11th June 2008 

Reasons for using Render Passes: Flexibility: Flexibility to do changes with very little rendering. More often the required changes can be done at the compositing stage. For example: with a specular pass, we are not worried having to re render the entire scene because the Highlights are too strong. We can simply change the opacity of the specular layer or if we need to “soften” the specularity we could blur that layer, when compositing. Or in worst case, scenario simple rerender the specular pass. Memory Management: Very often when rendering we hit the peak of Memory and a “Memory exception” get thrown. As not necessarily all object, with all their properties, are rendered together when using render layer (passes), the memory is managed much better. Also the option to “switch of” the render pass, makes it easier to render the same scene on different systems, based on what configuration the individual system is. This is very valuable to smaller companies with limited resources. Saving Render Time: Very often, trying to achieve a “more finer” image quality, literally multiplies render time. For Example: Blurred reflections will need more render time. With a reflection pass, we can blur the reflection when compositing. Note: we are not at all saying that the look is identical to the rendered reflection, however, not always does the scene need that intense accuracy. Relighting: One of the main reasons to render passes. Often the rendered sequence has to be composited with real life footage, and it is quite difficult for the Computer Graphics Image to match the lighting of the real world. Therefore, there is often a need to “relight”, using the lights of the compositing system and the layers within. One of the ways is using the “normal pass” which is explained in the tutorial “Pipleline techniques : Bend Normals”. There are many other techniques as well. Position Live objects(footage) within CG elements: Another common usage is when we need to have live footage (real life character) to be “between” certain CG. Using the Depth Map pass this can be achieved. Compositing Effects: There are tons of ways render passes help when compositing special effects. Commonly used particles, fogs, glows, etc or simple alpha or Occlusion pass when composited allows to enhance the look, and at time create a new effect altogether.   

Prem Moraes

 

Digitally signed by Prem Moraes DN: cn=Prem Moraes, o=Autodesk India Ltd., ou=M&E, email=prem.moraes@autodesk. com, c=IN Date: 2008.08.19 17:14:20 +05'30'

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