Annotations

Draw and manage rectangles, polygons, and points directly on the image.

Tools

Tool	Shortcut	How to use
Pan	P	Scroll to zoom, drag to pan
Select	V	Click to select; Delete to remove
Rectangle	R	Click and drag
Polygon	G	Click vertices; double-click or click near start to close
Point	O	Click to place

Select a tool from the toolbar or press the keyboard shortcut.

Exporting annotations

viewer.rois_df      # pd.DataFrame: id, x, y, width, height
viewer.polygons_df  # pd.DataFrame: id, points, num_vertices
viewer.points_df    # pd.DataFrame: id, x, y

Clearing annotations

viewer.clear_rois()
viewer.clear_polygons()
viewer.clear_points()
viewer.clear_all_annotations()

Styling

viewer.roi_color     = "#ff0000"  # rectangle color (hex)
viewer.polygon_color = "#00ff00"  # polygon color (hex)
viewer.point_color   = "#0000ff"  # point color (hex)
viewer.point_radius  = 5          # point radius in pixels

viewer.rois_visible     = False   # toggle visibility
viewer.polygons_visible = True
viewer.points_visible   = True

Reactive annotations in marimo

In marimo, wrap the viewer and reference widget.value to reactively access annotations in downstream cells:

@app.cell
def _(viewer, mo):
    widget = mo.ui.anywidget(viewer)
    return widget

@app.cell
def _(widget):
    import pandas as pd
    rois = widget.value.get("_rois_data", [])
    rois_df = pd.DataFrame(rois)
    return rois_df

The downstream cell re-runs automatically whenever you draw or delete an annotation.