If you want to use a Precomp node to speed up rendering, you need to have the Precomp node read in the output of the precomp script.
| 1. | Create a Precomp node. For more information on how to do this, see Creating Precomp Nodes. |
| 2. | In the Precomp node controls, click Render. Enter a frame range (for example, 1-100) in the dialog that opens and click OK. |
Nuke renders the output of the precomp script and saves the resulting image in the Precomp render path directory you specified when you created the Precomp node.
If you have activated the proxy mode and have specified a proxy file name in the output node, the rendered image is a proxy image.
| 3. | If the render finishes successfully, read file for output is automatically turned on in the Precomp properties. When this is checked, the Precomp node turns green and reads in the rendered precomp image rather than calculates the output of the precomp script. The word (Read) and the name of the image read in are also displayed on the Precomp node in the Node Graph to indicate this. |
| 4. | In case there is an error opening the rendered output of the precomped nodes, select what to do from the missing frames dropdown menu in the Precomp properties: |
• error - display an error message on any missing frames.
• black - replace any missing frames with black.
• checkerboard - replace any missing frames with a checkerboard image.
• read input - display the result of the input tree rather than the rendered file on any missing frames.
When several Precomp nodes are used like this to replace sections in a large, complex node tree, the render times may become significantly faster.
NOTE: When rendering the output of the precomp script, Nuke automatically selects the Write node to use by first looking for an Output node. If it can't find any Output nodes, it tries to find a Write node, and sets Output node in the Precomp node controls to the name of the Write node. If it can't find any Output or Write nodes, it produces an error.
At any point, the Precomp node properties can be used to override what is set as the Output node in the precomped script. To do so, open the Precomp properties and the advanced controls. In the Output node field, enter the name of the Write node whose output you’d like to use. Make sure you also check enable. This check box allows you to toggle between the output node chosen by default and the output node you specified in the Output node field.
TIP: You can also use Write nodes in a similar manner and have their output read in from the rendered file rather than calculated using the nodes upstream.