What Is the Viewer Node in Blender Compositor?

The Viewer node in Blender's Compositor is an essential preview tool designed to give artists real-time visual feedback on intermediate stages of a node tree. Unlike the final output node, the Viewer node allows you to inspect the effect of specific adjustments, masks, passes, or color grades at any point in your compositing pipeline directly in the Backdrop or the Image Editor.

The Primary Purpose of the Viewer Node

In a non-destructive, node-based workflow, understanding how individual operations affect an image is crucial. The primary function of the Viewer node is to let you bypass the final output and visualize the data flowing through any specific connection. It acts as an internal display terminal for image data, allowing you to troubleshoot issues, fine-tune mask edges, inspect render passes like Cryptomatte or Z-depth, and verify color adjustments.

Viewer Node vs. Composite Node

While they look similar, the Viewer node and the Composite node serve distinct functions:

  • Composite Node: Dictates the final rendered output that is saved to your disk or sent to the final render window. Every functional compositing setup requires at least one active Composite node.
  • Viewer Node: Strictly an internal display tool. It does not affect the final render or file export. You can add, delete, or mute Viewer nodes without altering the rendered image.

How to Use the Viewer Node

  1. Manual Connection: Add a Viewer node by pressing Shift + A > Output > Viewer, then connect any image output socket directly into the Viewer’s image input socket.
  2. Node Wrangler Shortcut: With the built-in Node Wrangler add-on enabled, simply hold Ctrl + Shift and left-click on any node to automatically create or reconnect a Viewer node to that specific node.
  3. Viewing the Output:
    • Backdrop: Enable the Backdrop toggle in the Compositor header to display the preview directly behind your node tree. You can move the backdrop with Alt + Middle Mouse Button and zoom using V and Alt + V.
    • Image Editor: Open an Image Editor window and select Viewer Node from the image dropdown menu to see the preview in a dedicated panel.

Split Viewer Node

Blender also includes a Split Viewer node, which is a specialized variant. It takes two separate image inputs and splits the preview horizontally or vertically across the screen. This allows you to perform direct before-and-after comparisons of your composite without needing to switch connections back and forth.