polarization op• Data kinds: polsweep → image2d
• Call: import specularity; specularity.polarization_separate(images, angles_deg=(0.0, 45.0, 90.0, 135.0), max_violation_frac=0.0) (or opsspecular.get("polarization_separate"))
Split a polariser sweep into its unpolarised and linearly polarised radiance. → (diffuse, specular), both (H, W).
Fitting `I(t) = 0.5 (S0 + S1 cos 2t + S2 sin 2t)` per pixel gives
`I_min and I_max` in closed form, and the classical separation
(Wolff & Boult 1991; Nayar, Fang & Boult 1997) reads
`diffuse = 2 * I_min` (the unpolarised radiance)
`specular = I_max - I_min` (the linearly polarised radiance)
with `diffuse + specular = I_min + I_max` = the total scene radiance, so
nothing is lost or invented. Round-tripping
:func:polarization_render through this operator returns the inputs with a
maximum absolute error of 3.9e-16 for the four angles of a
division-of-focal-plane sensor and 4.4e-16 for a bare three-angle sweep
(measured in `tests/test_specularity.py`).
Read the names as shorthand. What is recovered exactly is the
unpolarised and polarised parts. Calling them diffuse and specular assumes
diffuse reflection is unpolarised and specular reflection is fully linearly
polarised — true near Brewster's angle for a dielectric, **false at normal
incidence**, where the specular reflection is unpolarised and this operator
returns all of it as "diffuse", and unreliable for metals. The polarisation
route is complementary to the colour route
(:func:specular_diffuse_split), not a replacement: it needs no illuminant
colour and works on textured, multi-material surfaces, but it needs a
favourable geometry.
*max_violation_frac* is the fraction of pixels allowed to fit a negative
minimum radiance before the call fails. The default 0 is fail-closed: a
negative fitted minimum means the modulation exceeded the mean, which no
analyser can produce, and it usually means the frames and *angles_deg* are
out of order. Raise it to clamp sensor-noise-level violations to zero as a
deliberate, recorded choice.
Raises `ValueError: *images* is not an (N, H, W)` stack of at
least 3 frames, or exceeds :data:MAX_LIGHTS / :data:MAX_STACK_ELEMENTS;
*angles_deg* does not match the frame count or leaves the fit
rank-deficient (two angles equal modulo 180); more than
*max_violation_frac* of the pixels fit a negative minimum.
• specular_photometric family guide
• 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.
• The canonical algorithm (author, year) and its uses are named in the family usage guide above.
• poc_polarization_specular — py -3.11 examples/poc_polarization_specular.py
• specular_photometric — py -3.11 examples/specular_photometric.py
image2d as input)polarization)polarization_render · polarization_dolp_map · polarization_stokes
*Provenance: specularity.py — SPECULAR 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.