Centroiding

timsTOF raw data is profile-like: the binary file stores one intensity value per scan per m/z index, spread across hundreds of mobility bins. Centroiding collapses that cloud of raw measurements into a compact list of peaks — each with a single m/z, intensity, and ion mobility value.

tdfpy provides two centroiding functions:

get_centroided_spectrum — high-level: reads a full frame from disk, applies optional noise filtering, and returns centroided peaks in one call.
merge_peaks — low-level: centroids pre-assembled NumPy arrays of m/z, intensity, and ion mobility values. Use this when you already have the raw arrays or need fine-grained control.

In practice, most workflows should call .centroid() directly on a Frame, DiaWindow, or PrmTransition object — that method delegates to get_centroided_spectrum internally.

Numba JIT backend

When Numba is installed (it is included in the default tdfpy dependencies), the core clustering loop runs as a JIT-compiled native function (_merge_peaks_numba_kernel). This is typically 5–20× faster than the pure-Python fallback for large frames. The backend is selected automatically:

# Numba used if available (default)
peaks = merge_peaks(mz, intensity, im)

# Force the Python fallback (useful for debugging or environments without Numba)
peaks = merge_peaks(mz, intensity, im, use_numba=False)

The first call after import triggers Numba's JIT compilation — expect a few seconds of overhead. Subsequent calls use the cached compiled kernel.

`get_centroided_spectrum`

Reads frame frame_id from the open TimsData connection, converts m/z indices to m/z values, assembles the raw peak arrays, optionally filters noise, and runs centroiding.

from tdfpy import timsdata_connect, get_centroided_spectrum

with timsdata_connect("experiment.d") as td:
    # Default: 1/K0 ion mobility, 8 ppm m/z tolerance
    peaks = get_centroided_spectrum(td, frame_id=1)
    print(peaks.shape)   # (N, 3) — columns: [m/z, intensity, 1/K0]

    # Tighter tolerances, CCS instead of 1/K0
    peaks = get_centroided_spectrum(
        td,
        frame_id=1,
        ion_mobility_type="ccs",
        mz_tolerance=5.0,
        im_tolerance=0.03,
    )

    # Noise filtering before centroiding (string shorthand)
    peaks = get_centroided_spectrum(td, frame_id=1, noise="mad")

    # Hard intensity threshold
    peaks = get_centroided_spectrum(td, frame_id=1, noise=500.0)

    # Composed pipeline + region exclusion + tuned filter
    from tdfpy import ChargeStateRegion, MadThreshold, VerticalNoiseFilter
    peaks = get_centroided_spectrum(
        td, frame_id=1,
        exclude=ChargeStateRegion(),
        noise=[VerticalNoiseFilter(min_streak_scans=5), MadThreshold(k=3)],
    )

    # Watershed centroider (integer-index space, no float-m/z binning)
    from tdfpy import WatershedCentroider
    peaks = get_centroided_spectrum(
        td, frame_id=1,
        centroid=WatershedCentroider(attach_scan_half_width=10, attach_mz_idx_half_width=3),
    )

The noise= parameter accepts the string shorthand ("mad", "percentile", "histogram", "baseline", "iterative_median"), a numeric absolute threshold, or any NoiseFilter instance / list — see Noise filters for the full hierarchy. The exclude= parameter accepts a ChargeStateRegion. The centroid= parameter swaps the centroiding algorithm — see Pipeline → Centroiders.

tdfpy.get_centroided_spectrum

get_centroided_spectrum(
    td: TimsData,
    frame_id: int,
    *,
    scan_range: tuple[int, int] | None = None,
    exclude: ChargeStateRegion | None = None,
    smooth: Smooth | None = None,
    noise: NoiseSpec = None,
    ion_mobility_type: Literal[
        "ook0", "ccs", "voltage"
    ] = "ook0",
    centroid: Centroider | None = None
) -> np.ndarray

Extract a centroided spectrum for a single frame.

Thin orchestrator over the :mod:tdfpy.pipeline ops. Threads a :class:~tdfpy.pipeline.RawSpectrum through optional scan-range restriction, region exclusion, intensity smoothing, and noise filtering, then hands it to the centroider — which decides whether to operate in integer index space (e.g. :class:~tdfpy.pipeline.WatershedCentroider) or after float conversion (e.g. :class:~tdfpy.pipeline.MergePeaksCentroider).

Default centroider is :class:~tdfpy.pipeline.MergePeaksCentroider. Pass smooth=Smooth(...) for a position-preserving box-sum/mean smoothing pre-step; the :class:~tdfpy.pipeline.WatershedCentroider additionally has its own seed-stabilising smoother via its smooth_*_half_width fields.

Returns an (N, 3) array of [mz, intensity, ion_mobility] centroids.

Source code in src/tdfpy/centroiding.py

def get_centroided_spectrum(
    td: TimsData,
    frame_id: int,
    *,
    scan_range: tuple[int, int] | None = None,
    exclude: ChargeStateRegion | None = None,
    smooth: Smooth | None = None,
    noise: NoiseSpec = None,
    ion_mobility_type: Literal["ook0", "ccs", "voltage"] = "ook0",
    centroid: Centroider | None = None,
) -> np.ndarray:
    """Extract a centroided spectrum for a single frame.

    Thin orchestrator over the :mod:`tdfpy.pipeline` ops. Threads a
    :class:`~tdfpy.pipeline.RawSpectrum` through optional scan-range
    restriction, region exclusion, intensity smoothing, and noise filtering,
    then hands it to the centroider — which decides whether to operate in
    integer index space (e.g. :class:`~tdfpy.pipeline.WatershedCentroider`) or
    after float conversion (e.g. :class:`~tdfpy.pipeline.MergePeaksCentroider`).

    Default centroider is :class:`~tdfpy.pipeline.MergePeaksCentroider`. Pass
    ``smooth=Smooth(...)`` for a position-preserving box-sum/mean smoothing
    pre-step; the :class:`~tdfpy.pipeline.WatershedCentroider` additionally
    has its own seed-stabilising smoother via its ``smooth_*_half_width`` fields.

    Returns an ``(N, 3)`` array of ``[mz, intensity, ion_mobility]`` centroids.
    """
    spectrum = read_spectrum(td, frame_id)
    if scan_range is not None:
        spectrum = subset_scans(
            spectrum, scan_num_begin=scan_range[0], scan_num_end=scan_range[1]
        )
    if exclude is not None:
        spectrum = exclude_region(spectrum, exclude, td=td, frame_id=frame_id)
    if smooth is not None:
        spectrum = smooth.apply(spectrum)
    filters = coerce_filters(noise)
    if filters:
        spectrum = apply_noise(spectrum, filters, td=td, frame_id=frame_id)

    if spectrum.empty:
        logger.warning("Frame %d has 0 peaks, returning empty spectrum", frame_id)
        return np.empty((0, 3), dtype=np.float64)

    centroider = centroid if centroid is not None else MergePeaksCentroider()
    centroids = centroider(
        spectrum, td, frame_id, ion_mobility_type=ion_mobility_type
    )
    logger.info(
        "Centroided frame %d: %d raw → %d centroids",
        frame_id, len(spectrum), len(centroids),
    )
    return centroids

`merge_peaks`

Centroids pre-assembled arrays. The algorithm is a greedy intensity-ordered scan: starting from the highest-intensity raw peak, every neighbouring peak within the m/z and ion mobility tolerances is merged into a single centroid via intensity-weighted averaging. Merged peaks are marked as used and skipped in subsequent iterations.

Parameter	Default	Notes
`mz_tolerance`	`8.0`	Width of the m/z matching window
`mz_tolerance_type`	`"ppm"`	`"ppm"` or `"da"`
`im_tolerance`	`0.1`	Width of the ion mobility window
`im_tolerance_type`	`"relative"`	`"relative"` (fraction of 1/K0) or `"absolute"`
`min_peaks`	`3`	Raw peaks required to form a centroid; set to `0` or `1` to keep all
`max_peaks`	`None`	Cap on output peaks (highest-intensity first)
`use_numba`	`True`	Set to `False` to force the Python fallback

import numpy as np
from tdfpy import merge_peaks

mz  = np.array([500.001, 500.002, 700.005, 700.006, 700.007])
inten = np.array([8000.0,  4000.0,  6000.0,  5000.0,  3000.0])
im  = np.array([0.85,     0.85,    0.92,    0.92,    0.92])

peaks = merge_peaks(mz, inten, im, mz_tolerance=10.0, min_peaks=2)
print(peaks)
# shape (2, 3): two centroided peaks, columns [m/z, intensity, 1/K0]

Noise filtering vs `min_peaks`

The noise= parameter (available on get_centroided_spectrum, .centroid(), and get_raw_peaks) chains noise filters before the centroider runs — intensity thresholds, the vertical-IM streak filter, or any combination. Intensity-based estimators have a fundamental limitation: they can't distinguish low-abundance real signal from electronic noise. Methods like MadThreshold are anchored to the median of the intensity distribution — if your sample has sparse signal, the threshold can rise above legitimate low-abundance peaks.

A more reliable strategy is to increase min_peaks instead:

# Prefer: raise min_peaks to filter noise without discarding low-abundance signal
peaks = merge_peaks(mz, intensity, im, min_peaks=5)

# Noise arises from single scans; real peaks appear across multiple scans.
# min_peaks=5 means a centroid must be supported by at least 5 raw measurements.

Because electronic noise typically manifests as a singleton in a single scan, requiring several supporting raw peaks is a structural filter — it targets the origin of noise rather than its intensity. The VerticalNoiseFilter extends this idea to the IM axis, requiring peaks to appear as vertical streaks across consecutive mobility scans.

Use intensity-based noise= filters only if you have a calibrated threshold or a method validated for your acquisition; always verify against noise=None first.

tdfpy.merge_peaks

merge_peaks(
    mz_array: np.ndarray,
    intensity_array: np.ndarray,
    ion_mobility_array: np.ndarray,
    mz_tolerance: float = 8.0,
    mz_tolerance_type: Literal["ppm", "da"] = "ppm",
    im_tolerance: float = 0.1,
    im_tolerance_type: Literal[
        "relative", "absolute"
    ] = "relative",
    min_peaks: int = 3,
    max_peaks: int | None = None,
    peak_noise_filter: bool = False,
    peak_noise_window: float = 0.1,
    peak_noise_end_fraction: float = 0.1,
    use_numba: bool = True,
) -> np.ndarray

Centroid profile-like peaks using m/z and ion mobility tolerances.

This function implements a greedy clustering algorithm that centroids raw peaks (similar to profile mode data) within specified m/z and ion mobility windows. Peaks are processed in descending order of intensity, and nearby peaks are combined using intensity-weighted averaging to produce centroided peaks.

Parameters:

Name	Type	Description	Default
`mz_array`	`np.ndarray`	Array of m/z values from raw/profile-like data	required
`intensity_array`	`np.ndarray`	Array of intensity values	required
`ion_mobility_array`	`np.ndarray`	Array of ion mobility values (1/K0 or CCS)	required
`mz_tolerance`	`float`	Tolerance for m/z matching during centroiding	`8.0`
`mz_tolerance_type`	`Literal['ppm', 'da']`	Type of m/z tolerance - "ppm" or "da" (daltons)	`'ppm'`
`im_tolerance`	`float`	Tolerance for ion mobility matching during centroiding	`0.1`
`im_tolerance_type`	`Literal['relative', 'absolute']`	Type of ion mobility tolerance - "relative" or "absolute"	`'relative'`
`min_peaks`	`int`	Minimum number of nearby raw peaks required to form a centroid. Set to 0 or 1 to keep all peaks (no filtering).	`3`
`max_peaks`	`int \| None`	Maximum number of centroided peaks to return (keeps highest intensity)	`None`
`peak_noise_filter`	`bool`	If True, after each centroid is formed suppress raw points within ±`peak_noise_window` Da of the anchor m/z and inside the centroid's IM window whose intensity falls below a linear threshold that decays from the anchor point's raw intensity at zero distance to `anchor * peak_noise_end_fraction` at the window edge. This kills TOF satellite/ringing noise around bright peaks without eliminating nearby real peaks that exceed the ramp. Comparison is point-to-point against the raw anchor intensity (not the summed centroid). Defaults to `False`.	`False`
`peak_noise_window`	`float`	Half-width in Da on each side of the anchor m/z over which the peak-noise ramp is applied. Defaults to `0.1` Da.	`0.1`
`peak_noise_end_fraction`	`float`	Fraction of the anchor's raw intensity used as the suppression threshold at `peak_noise_window` distance. Defaults to `0.1` (10%).	`0.1`

Returns:

Type	Description
`np.ndarray`	np.ndarray: Array of shape (N, 3) containing centroided peaks. Columns are: [mz, intensity, ion_mobility]

Example

mz = np.array([100.0, 100.001, 200.0])
intensity = np.array([1000.0, 500.0, 2000.0])
im = np.array([0.8, 0.8, 0.9])
peaks = merge_peaks(mz, intensity, im, mz_tolerance=10, mz_tolerance_type="ppm")