Problem

Users often need to merge multiple annotation masks into a single mask. This is especially common when using ML-assisted auto-annotations or interactive tools such as the magic wand, which frequently produce overlapping or fragmented masks. Label Studio currently lacks a native front-end capability to merge multiple masks.

Added feature

• Feature branch: https://github.com/hua-cv-team/label-studio-merge-tool/tree/merge-tool-implementation

The tool allows users to select multiple mask annotations in the labeling interface and merge them into a single mask entirely from the front end. This functionality is currently used in our organization’s annotation workflow and has proven useful when refining ML-generated or magic wand–created masks and combining partially drawn masks. The merge functionality works for all drawn masks and any mask annotations that contain RLE information.

User Stories

• As an annotator, I want to merge multiple mask annotations into one so that I
  can quickly refine ML-generated or magic wand–created masks.

• As a project manager, I want annotators to merge masks directly in the UI so
  that segmentation workflows are faster and more consistent.

• As an ML engineer, I want merged, cleaner masks so that the quality of training
  data is improved.

Usage

To merge two or more masks:

1. In the annotations side panel, select (highlight) two or more mask annotations you want to combine.
2. Click the Merge button located above the annotations panel, next to the Hide/Unhide button.
3. The selected masks will be merged into a single mask annotation.

prd issue: #9233