Secondary Outputs

To get started, let's open the Maya scene, outputs.ma.
(Where are the tutorial files?)

1 — SECONDARY OUTPUTS

Render the Maya scene, outputs.ma, with RenderMan.
Render-> Render Current Frame
You should get an image like the one below:

The final image

The rendering above is the final image, a combination of many different effects and surface qualities: diffuse coloring, specularity, reflections, etc. Sometimes it is advantageous to render these various qualities into their own image, as secondary passes. RenderMan allows you to render secondary passes at the same time the final image is rendered, allowing the final image to be output with a collection of secondary passes simultaneously. Secondary passes such as specularity, reflections, shadows, occlusion, etc., can be composited together after the fact, when specific elements of an image (like specularity) can be tweaked without having to render the whole image again. In this tutorial we'll go through the workflow of setting up secondary outputs with RenderMan for Maya.

2 — ADDING A SECONDARY OUTPUT

First, we'll add a secondary output for the shadows, which will output the shadows into their own image file. To do this, follow these instructions:

1) Open the RenderMan Globals and select the Passes tab.
2) Locate the Output subtab of the Passes tab.
3) Open the pull-down menu (which looks like a downward arrow) next to the Output field and select:
Create Ouput-> DiffuseDirectShadow

That's it. You have now created a secondary output for a shadow. Whenever the final image is rendered, a secondary output for the shadow will be created at the same time. When this is accomplished, simply render again.

As before you should get the same final image:

The final image

But now you'll also have the shadow output. This image is automatically stored in your current Maya project and is located in the RenderMan folder, under the name of the maya file. In this case the secondary output for the shadow can be found here:
RenderMan/outputs/images/outputs_DiffuseDirectShadow.iff

RenderMan Studio users that are rendering to 'it' can see the secondary outputs via the Catalog view, with the images cascaded below each primary output.

The secondary output for the image looks like this:

The secondary output for the shadow.

3 — ADDING MORE OUTPUTS

Using the same workflow, we can make secondary outputs for specular, reflections, and diffuse values. Do that now.

1) Open the RenderMan Globals and select the Passes tab.
2) Locate the Output subtab of the Passes tab.
3) Open the pull-down menu next to the Output field and select:
            Create Ouput-> SpecularDirect
4) Open the pull-down menu next to the Output field and select:
            Create Ouput-> DiffuseDirect
5) Open the pull-down menu next to the Output field and select:
            Create Ouput-> SpecularIndirect

Now render again. In addition to the final image and the shadow output, you'll also get the addtional secondary outputs in your directory, RenderMan/outputs/images/

The secondary output for the specularity.

The secondary output for the diffuse.

The secondary output for the reflection.

These individual layers are now ready for compositing.

4 — MANAGING SECONDARY OUTPUTS

You'll notice that the pull-down menu next to the Output field has a list of the secondary outputs we just created. This pull-down menu can be used to toggle back and forth between secondary outputs. When a secondary output is selected, the parameters particular to that secondary output appear below it. Using these parameters any secondary output can be configured. The file format, the filter, the quantization, and more can be changed.

From this pull-down menu layers can also be deleted. Since we are done with this exercise, delete all of the secondary outputs that we just created:

1) Locate the Output subtab of the Passes tab in the Render Globals.
2) Open the pull-down menu next to the Output field and select:
Create Output-> Delete Output

Usually secondary outputs should be created during the final render, but in certain situations you'll want to create secondary outputs during other pre-passes, like shadow passes, reference passes, etc. By switching pass types (using the Pass pull-down menu in the Passes tab) you can add secondary passes to any individual pass that you require.

5 — SUMMARY

Secondary Ouputs, useful for compositing techniques, can be created with RenderMan for Maya. RenderMan for Maya is flexible when it comes to how these secondary outputs are created. Because the pixels for the secondary outputs are output at the same time that the pixels for the final image are calculated, RenderMan is very efficient when creating these outputs. In fact, secondary outputs require minimal additional overhead.

Prev | Next