Heatmaps

A heatmap is a scalar raster, not a colour image or a binary segmentation mask. Attach one to a detection with media-space bounds, raster width and height, row-major values, and the model's optional threshold. The renderer colours small maps when their frame is presented and prepares larger maps ahead of playback when a worker is available. A large map may appear after its frame if preparation has not finished yet. It does not infer, track, or decide which detections should exist.

This playground uses Patrick's frozen FoundAD inference and temporally confirmed bolt and stick detections. Unconfirmed hot spots are not sent to the renderer. The fixture's heatmap values are 16-bit integer scores with valueScale: 1 / 65535; a caller with a raw anomaly_map[y][x] can instead flatten it directly as floats with the default scale of 1.

const heatmap = {
  bounds: {
    x: imageWidth / 2,
    y: imageHeight / 2,
    width: imageWidth,
    height: imageHeight,
  },
  width: anomaly_map[0].length,
  height: anomaly_map.length,
  values: anomaly_map.flat(),
  threshold: anomaly_threshold,
};

// Put this semantic heatmap on a Detection in a DetectionFrame.
session.setPresentation({
  renderers: [annotationRenderers.heatmap()],
});
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thresholdScale, minimumAlpha, opacity, maximumScore, and colorStops are presentation choices. The default cutoff is the score's own threshold and colours use the same fixed 0-to-1 score scale across frames, while the cutoff controls transparency. Set maximumScore if the model uses a different range; lower the cutoff only when you want to show weaker evidence. In the pebbles demo, the cutoff is 75% of the model threshold and only tracker-confirmed detections are displayed. A lower-resolution anomaly_map can cover full-image bounds without making a full-resolution texture.

When focus is enabled, the undimmed region follows the visible heatmap samples rather than the detection's rectangular bounds. Changing the cutoff or opacity updates both the heatmap and its focus cutout.

Each map is limited to 16,777,216 raster pixels, and the visible maps across all heatmap renderers share that same per-frame pixel budget. Maps beyond the budget are skipped with a console warning. The prepared raster cache is bounded and does not retain heatmaps for the whole video. For large maps, leave worker render preparation enabled; a main-thread-only setup may pause while it prepares a raster.