vol_equalize — 3D `gray` op

• Data kinds: voxel → voxel

• Call: import fullseye as fs; fs.ledger.vol_equalize(vol, nbins=256, mask=None) (to call the implementation directly, import volgray; volgray.vol_equalize(vol, nbins=256, mask=None); from the registry, ops3d.get("vol_equalize"))

Usage

Histogram equalisation of a volume (HALCON `equ_histo_image`).

Builds an *nbins*-bin histogram over the volume's `[min, max]` range,

takes its cumulative distribution as a monotone LUT, and maps every voxel

through it — the output lives in `(0, 1]` and its histogram is

(approximately) flat. With *mask* (thresholded at `> 0.5`, the volops

convention) the **histogram is computed from the masked voxels only while

the LUT is applied to the whole volume** — exactly the HALCON

`reduce_domain + equ_histo_image` domain behaviour, and the right

tool when a dominant background (e.g. air around a CT subject) would

otherwise swallow the whole dynamic range.

A constant volume is returned unchanged — normalising a flat volume

would amplify floating-point dust into full-scale garbage (fail-honest,

not fail-loud; see the module docstring).

Parameters

----------

vol : array_like, shape (D, H, W)

Input volume (coerced to float64; NaN/Inf rejected).

nbins : int

Histogram bins, `>= 2`. More bins = finer LUT (the mapping is

piecewise-constant per bin — an approximation, documented above).

mask : array_like, shape (D, H, W), optional

Histogram domain. Must match *vol*'s shape and select at least one

voxel (an empty domain has no histogram — fail-closed).

Returns

-------

ndarray, shape (D, H, W), float64

The equalised volume in `[0, 1]` (constant input: the input itself).

Raises

------

ValueError

Non-3-D / non-finite input, `nbins < 2`, a mask shape mismatch, or

an empty mask.

References (sample data, literature)

• 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.

Runnable examples (verified samples that actually call this op)

• gray_window_level — py -3.11 examples_3d/gray_window_level.py

Ops the type connects to (they accept `voxel` as input)

voxel_to_mips · voxel_to_mesh · signed_distance_field · to_points · sobel3d · hessian3d · curvature_maps · edt_jfa

Same category (`gray`)

vol_window_level · vol_gamma · vol_stretch

*Provenance: volgray.py — 3D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

vol_equalize — 3D gray op