Blob Tracker: Every Parameter Explained

The Blob Tracker detects motion in your video and draws overlays on moving areas in real time. Each parameter changes either the detection behavior or the overlay style. This guide covers every one of them with concrete values to try.

Detection

Threshold (10–100)

Motion detection sensitivity. The tracker compares each frame to the previous one, pixel by pixel. If the difference exceeds the threshold, the pixel is flagged as moving.

• Threshold 15: picks up the smallest micro-movements. Background noise, a hand trembling, shadows shifting, everything triggers blobs. Useful for very static clips with subtle motion.
• Threshold 25 (default): clean balance. Filters ambient noise, keeps body and face movements.
• Threshold 50–70: only reacts to fast, sharp movements. A dancer gets tracked, someone walking slowly does not.
• Threshold 90+: only maximum-contrast zones register. Scene transitions, light flashes, impacts.

Min Blob Size (20–500 px)

Minimum pixel count a blob needs to be displayed. Filters detection noise.

• 20–40 px: micro-blobs everywhere. The tracker reacts to fingers, lips, reflections. Dense and twitchy.
• 80 px (default): ignores noise, keeps hand shapes, heads, torsos.
• 200–500 px: only large motion blocks show up. A full body moving, a group dancing. Clean and readable.

Overlay

Effect Style

Eight rendering styles for the blob overlays:

• Basic: plain circle. Direct readout of blob size and position.
• Frame: rectangular frame. Surveillance, military tracking look.
• L-Frame: L-shaped corners at each blob corner. Lighter than Frame, UI/HUD look.
• X-Frame: X cross on the blob center. Targeting reticle.
• Scope: circle with built-in crosshair. Sniper/radar feel.
• Dash: dashed outline. Photoshop selection, cutout, analytical mood.
• Grid: grid overlaid on the blob. Data visualization, thermal sensor.
• Glow: soft diffuse halo. The most organic of the eight, works for music and live visuals.

Blob Color

Colour of all overlays, in hex. White (#ffffff) works everywhere. Green (#00ff00) gives military look. Cyan (#00ffff) pushes toward sci-fi. Pick colours that contrast with your footage.

Stroke Width (0.5–3 px)

Outline thickness. At 0.5, overlays are thin and technical. At 3, they're thick and readable from a distance, better for projections and stage screens.

Bounding Size (0.5–3x)

Multiplies bounding box size without affecting detection. At 0.5, overlays hug the motion tightly. At 2–3x, they overflow and overlap, creating denser graphic compositions.

Fill Opacity (0–40%)

Fills blob interiors with the chosen colour. At 0%, only the outline shows. At 20%, blobs become translucent coloured zones. At 40%, the overlay dominates the image, useful for masking the footage and keeping only shapes.

Behavior

Trail Length (0–20 frames)

Number of previous frames shown as ghost trails behind each blob. Opacity fades with age.

• 0: no trail. Each blob appears and disappears within the current frame. Reactive and dry.
• 3 (default): slight persistence. Motion leaves a short trace that gives directional context.
• 10–15: long ghost trails. Blobs trace visible trajectories, like light painting.
• 20: max trails. The screen fills with ghosts, past motion stays visible for a long time.

Show Label

Displays the pixel count inside each blob (in thousands). Data/analytics look. Turn it off for a more graphic result.

Connections + Connection Range (1–6x)

Draws lines between nearby blobs. Range controls maximum connection distance. Low range (1–2): only blobs that nearly touch get linked. High range (5–6): the tracker draws a network of lines across the whole image. Good for multi-person scenes.

Starting Presets

• Clean surveillance: Style Frame, colour #00ff00, stroke 1, trail 0, labels ON, threshold 30, min size 100
• Organic live visual: Style Glow, colour #ff00ff, stroke 2, trail 12, fill 15%, connections ON range 4, threshold 20
• Minimal data art: Style Dash, colour #ffffff, stroke 0.5, trail 0, labels ON, connections ON range 2, fill 0%, threshold 35, min size 150
• Light painting: Style Basic, colour #00ffff, stroke 1.5, trail 20, fill 10%, connections OFF, threshold 15, min size 30

Open the Blob Tracker, load a video with motion, and start by adjusting threshold and style. Changes show instantly in the preview.

Outils utilisés

• Blob Tracker

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