typed op• Data kinds: counts → counts
• Call: fullseye.apply(img, "tb_tcspc_background_subtract", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
*No figure: this op takes counts as input. A Studio program starting from an image cannot reach that type — see the runnable examples below for how it is used.*
Remove the ambient-light / dark-count floor from an arrival-time histogram.
Outdoors, most of what a dToF sensor counts is sunlight: a roughly uniform
pedestal under the return pulse. It biases the centroid toward the middle of
the window (a floor of `b` per bin pulls the first moment toward
`window/2`) and it inflates the apparent signal, so it is removed before
any depth or lifetime estimate.
The level is estimated by *method* and then subtracted (the sign trap:
the result is `hist - level, clipped at 0, never hist + level`):
• `"median"` (default) — the median of every bin. Robust while the pulse
occupies well under half the window, which is the normal dToF case.
• `"leading"` — the mean of the first *leading_bins* bins, the classical
choice when the pulse is known to arrive late (a far target).
• `"trailing"` — the mean of the last *leading_bins* bins, for
fluorescence decays where the tail is background.
• `"quantile"` — the given *quantile* of all bins, for tuning by hand.
*leading_bins* defaults to `None = min(8, len(hist))`, so the default
call works on a short histogram instead of raising over a constant nobody
chose (a fixed default of 8 made `method="leading"` fail on any histogram
with fewer than 8 bins).
*scale* multiplies the estimated level before subtraction (`scale=1.2` for
a deliberately aggressive removal). Clipping at 0 means the result is a valid
non-negative histogram that the rest of this module will accept.
Ground truth: on a noiseless histogram with a known flat pedestal of 20
counts/bin under a 5000-photon pulse covering 5.1% of the window, the median
estimate recovers 20.000000 and the returned histogram equals the pedestal-
free pulse exactly (measured area error 0.0, pinned in the tests).
Returns a float64 1-D histogram of the same length as *hist*.
Raises `ValueError`: negative, non-finite or non-1-D *hist*, an unknown
*method*, a *leading_bins* outside `[1, len(hist)]`, a *quantile* outside
`[0, 1]`, and a negative *scale*.
Typed bridge of the photon op `tcspc_background_subtract into the 2-D evolution registry: the same implementation, called under the op(v, a, b) convention. a drives quantile (default 0.5) and b drives scale` (default 1).
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• (none yet)
counts as input)identity · tb_spad_deadtime_apply · tb_spad_deadtime_correct · tb_tcspc_coates_correct · tb_tcspc_irf_convolve · tb_dtof_depth · tb_countrate_to_counts · tb_counts_to_countrate
typed)tb_points_to_voxel · tb_estimate_point_normals · tb_iss_keypoints · tb_angle_3points · tb_project_points · tb_render_point_depth · tb_statistical_outlier_removal · tb_radius_outlier_removal
*Provenance: ops.py — 2D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.