artifact op• データ種: sinogram → sinogram
• 呼び出し: import tomography; tomography.beam_hardening_apply(sinogram, high_energy_fraction=0.5, attenuation_ratio=0.4) (または opstomography.get("beam_hardening_apply"))
単色サイノグラムを多色にする —— カッピングの発生源。
> 以下の詳細説明は原文のままです —— 要約と見出しは訳出済み。
A real X-ray tube emits a spectrum, and low-energy photons are absorbed more,
so the beam that survives a thick path is *harder* (higher mean energy) and
therefore attenuated less per unit length than the beam that survives a thin
one. The line integral stops being linear in path length, and the
reconstruction of a uniform object comes back with a depressed centre: the
cupping artefact.
The two-spectrum model used here is the smallest one that is physics and not a
curve::
I/I0 = (1-w) exp(-p) + w exp(-k p)
p_meas = -ln(I/I0)
with *w* the fraction of the beam at the high energy and *k < 1* its relative
attenuation. It is exact at `p = 0`, concave everywhere, and monotone — so
it is invertible, which is what :func:beam_hardening_correct inverts.
Measured on a uniform disc (radius 60 px in 256 px, density 1/60 so the peak
line integral is 2.0) at `w = 0.5, k = 0.4`: the FBP reconstruction's
centre-to-rim ratio drops to 0.9312, against 0.9981 before hardening,
and :func:beam_hardening_correct returns it to 0.9981 — the clean value
in all four digits. (The clean ratio is 0.9981 rather than exactly 1 because
of the detector sampling discussed in :func:filtered_backprojection. The
cupping is the 6.7-point drop, not the 0.2-point one.)
:param sinogram: `(n_angles, n_detectors)` monochromatic line integrals,
which must be `>= 0`.
:param high_energy_fraction: *w*, in `[0, 1)`. 0 is a monochromatic beam and
the operator is then the identity.
:param attenuation_ratio: *k*, in `(0, 1)`. 1 is again monochromatic.
:returns: `(n_angles, n_detectors)` float64 hardened sinogram.
:raises ValueError: on a negative sinogram (a negative line integral is not a
measurement this model can harden — the logarithm of the transmitted
intensity has already gone wrong upstream), or parameters outside range.
• サンプルデータ カタログ(DL URL / ライセンス) — 2-D は skimage.data(BSD/public)+ 合成、3-D は実データ源(Stanford/PDS 等)の DL URL。
• 演算子の来歴・参考文献 — この op 族の元になった研究/手法の出典。
• アルゴリズムの正典(著者・年)と用途は上記ファミリ使い方ガイドに記載。
• ct_reconstruction — py -3.11 examples/ct_reconstruction.py
sinogram を入力に取れる)backproject_sinogram · filtered_backprojection · sart_reconstruct · beam_hardening_correct · ring_artifact_apply · ring_artifact_remove · metal_trace_interpolate · sinogram_center_of_rotation
artifact)beam_hardening_correct · ring_artifact_apply · ring_artifact_remove · metal_trace_interpolate
*Provenance: tomography.py — TOMOGRAPHY operator registry. この per-op ノートは tools/opdocs.py md が自動生成(手編集しない)。*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.