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The active-contouring brush

Tracing a feature by hand is slow. The active-contouring brush — the flood toggle in a feature's panel, or the F key — fills a whole region in one stroke instead. It reads the brightness of the pixel under your cursor and grows outward into the connected area of similar-brightness pixels, stopping where the brightness changes. That makes it snap to the edges of membranes, filaments, granules, and other well-defined boundaries.

The active-contouring brush filling a feature in one stroke, snapping to its edges.

How to use it

  1. Select the feature you want to annotate, then turn on flood (the checkbox in its panel, or press F).
  2. Set the brush size with CTRL + scroll — this caps how far a single stroke can reach (shown in px and nm).
  3. Draw over the feature with the left mouse button; each stroke fills the connected region of similar brightness under the cursor. Erase as normal with the right mouse button.

What the sensitivity does

A sensitivity slider appears when flood is on (the - / = keys adjust it too). The brush fills pixels whose brightness falls within a band around the one under your cursor: lower sensitivity widens that band, filling more but bleeding past weak edges; higher sensitivity narrows it, filling less and stopping at fainter boundaries.

Tip

Flood works best on a clean image. Blur the tomogram with the filters so a whole membrane or granule reads as one contiguous region and fills in a single click. Filters change only what you and the brush see — the network still trains on the raw tomogram.