Motion brushes and masks let you target selected regions of a still image for animation. For better control, mark the smallest useful area, apply restrained directional movement, and review each result for unwanted motion before expanding the effect.
What Motion Brushes and Masks Control
Motion brushes and masks provide regional motion control in image-to-video workflows. Instead of asking the system to animate the entire image uniformly, you paint or mask the part that should move and then specify how it should move. The cited Runway workflow includes horizontal, vertical, proximity, and ambient controls, while the cited Kling workflow uses motion vectors such as direction and intensity.
These controls can help isolate movement in details such as hair, shoelaces, or water while asking for a face, product body, background, mountains, or sky to remain comparatively stable. That stability is an intended outcome, not a guarantee: generation behavior can vary, so the result still needs inspection.
A Practical Selective-Motion Workflow
Start by deciding exactly which object or detail should move. Select the smallest relevant region, but cover the intended object completely enough to avoid an incomplete effect. The AI Wiki tutorial recommends using a smaller brush for precision and erasing any accidental coverage. This matters because an overly broad painted area may animate an entire person when only one body part was intended to move.
Next, assign a restrained direction or intensity. In a portrait, that could mean targeting hair while asking for the face and background to remain still. For a product image, it could mean selecting shoelaces while leaving the product body stable. In a landscape, it could mean masking water while asking for the mountains and sky to remain still. These are source-reported workflow examples, not assured results.
Generate a preview and compare it with the intended motion plan. Check whether the selected region moves in the requested direction and whether unselected areas remain comparatively stable. If the wrong elements move, reduce or correct the mask. If the direction is wrong or excessive, revise the motion setting and try another restrained generation before increasing complexity.
Troubleshooting and Common Questions
When too much of the image moves, inspect the mask boundary first. Remove coverage from nearby objects and use a smaller brush around detailed edges. Accurate masks can take practice, and broad coverage can cause motion to spread beyond the intended feature.
When movement goes the wrong way, reduce the directional instruction or intensity and test again. Treat each generation as a check rather than assuming that painted and unpainted regions will behave perfectly. A useful review asks three questions: Did the intended region move? Did it move in the intended direction? Did the rest of the image remain comparatively stable?
Tool availability is another possible source of confusion. The classic Runway Motion Brush implementation belonged to Gen-2, which the AI Wiki source says became unavailable on May 11, 2025. Later models may use different controls. Because the supplied sources are third-party pages, confirm current interface names and model support in official documentation or the product interface.
Conclusion
A practical selective-motion workflow is iterative: define a precise region, apply restrained movement, inspect selected and unselected areas, and refine the mask or direction. Before attempting a complex animation, open the current interface or official documentation for your chosen AI video tool, confirm that regional motion controls are supported, and run a small test on one narrowly masked region.
Disclosures and limitations
- This article was prepared with AI assistance from the supplied AI Wiki and Vuela.ai research sources. Both are third-party sources, so current interfaces, model support, availability, pricing, and credit requirements should be verified through official product information.
- No affiliate relationship was supplied for this article. Any future product links or recommendations should disclose applicable affiliate relationships and must not imply independently verified testing.
Sources
- Runway Motion Brush Tutorial – Control AI Video Movement | AI Wiki — Artificial Intelligence Wiki
- Kling Motion Brush review (2026): paint where motion happens — vuela.ai
- Amazon.com : motion mask — amazon.com
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