Feedback
Feedback combines an earlier image with the image arriving now. A moving object can leave a trail, repeated copies can recede into a tunnel, or a picture can gradually build up over time.
Use feedback when the visual should remember what happened before. For a first experiment, use moving footage with bright shapes against a dark background so the trail is easy to see.
Try a simple trail
Section titled “Try a simple trail”Open the Fading Trails example as an editable project. Its guide explains how to open the example and replace its demonstration source.
- Play the project and inspect the Fading Trails layer. The other layer, Motion sample — replace with camera or video, supplies the demonstration image.
- In the Rack, change Retention per second. Higher retention keeps earlier images visible for longer; lower retention lets them disappear sooner.
- Change Source injection to control how strongly the new image contributes to the trail.
- Use Clear history when you want to discard the accumulated image and start again. Return a held clear control to its off state to let history build up.
Replace the demonstration source with your footage and repeat the experiment. The effect and its controls stay connected. See Sources and Project Inputs for source replacement.
What makes a feedback effect
Section titled “What makes a feedback effect”Most feedback effects combine three things:
| Part | What it changes |
|---|---|
| Retained image | Gives the next image something to remember |
| Fade or transformation | Makes that memory decay, move, turn, blur or change color |
| New source | Adds the current picture to the accumulated result |
The project may expose these as Rack controls. Their names depend on the effect: Fading Trails uses Retention per second, while Zoom Tunnel exposes History fade and movement controls.
Move the retained image
Section titled “Move the retained image”A small transformation repeated on each new frame makes earlier images travel across the composition.
In Zoom Tunnel, inspect the Zoom Tunnel layer and its Move previous frame node. Change History zoom X and History zoom Y in the Rack to see how scaling the retained image builds the tunnel. History fade controls how the older copies fade while Source injection brings in the current source.
Compare this with Spiral, which adds rotation, or Directional Smear, which moves the history in a direction.
Limit where feedback appears
Section titled “Limit where feedback appears”A mask lets an effect act on a chosen region rather than the whole image.
In Masked Feedback, inspect the Masked Feedback layer. Its Shape and Apply Mask nodes limit the result. Change Mask width and Mask height in the Rack and watch which parts remain visible. Read Masks + Compositing for another editable example of using a mask.
Previous Pass and Previous Frame
Section titled “Previous Pass and Previous Frame”These names describe different images you can use in a graph:
- Previous Pass is the current image entering a card from the stack below it. It does not remember earlier frames.
- Previous Frame is retained imagery from the preceding step. It supplies the memory used by a feedback effect.
If an effect changes the current picture but never leaves a trail, check whether it is using a retained image. Layers and the stack explains how the current image flows through a composition.
Use the effect with your existing composition
Section titled “Use the effect with your existing composition”When adding Fading Trails to your project, select the Fading Trails layer and connect its source to your existing content. Leave Motion sample — replace with camera or video out unless you want that demonstration footage too.
Follow Add reusable layers for the layer selection and connection steps. The controls needed by the selected effect travel with it.
When the result is not what you expected
Section titled “When the result is not what you expected”- No visible trail: try a moving source, increase retention, and check that Clear history is not held on.
- The image becomes too busy: reduce how much new imagery enters, shorten retention, or clear the accumulated image before trying again.
- Old shapes remain after replacing the source: clear history to start from the new source.
- You want to hold the image deliberately: explore Freeze/Hold/Clear to compare retaining, freezing and resetting an image.
For reusing a result in another part of the composition, continue with Shared Textures.