watervision op• Data kinds: none → table (an op determined by its arguments alone — it takes no image or data input)
• Call: import fullseye as fs; fs.ledger.wet_surface_appearance(albedo, roughness, water_film_um, view_deg, light_deg, n_water=None) -> 'dict' (to call the implementation directly, import watervision; watervision.wet_surface_appearance(albedo, roughness, water_film_um, view_deg, light_deg, n_water=None) -> 'dict'; from the registry, opsoptics.get("wet_surface_appearance"))
• GPU: none (CPU reference implementation only)
The darkening and the gloss of a surface under a thin water film (Lekner & Dorf 1988; Twomey et al. 1986) -> dict.
A dry diffuse surface of albedo a returns a of the light. Under a water film the light that the surface scatters upward reaches the water-air interface; the part beyond the critical angle (and the Fresnel share below it) is reflected back down, hits the surface again and is partly absorbed again. With r the hemispherical, cosine-weighted internal reflectance of the interface (computed by quadrature, about 0.47 for water) and R_s the Fresnel reflectance of the incoming light at light_deg, the geometric series of the trapped light gives, for a Lambertian surface, a_film = a (1 - R_s) (1 - r) / (1 - a r). This is below a for every a in (0, 1) and the darkening is stronger for darker surfaces (a = 0.5 loses about a third). water_film_um enters only through an assumed coverage c = 1 - exp(-film / 2 um) (a film thicker than a few micrometres wets all the roughness; interference in films thinner than a wavelength is not modelled), wet_albedo = (1 - c) a + c a_film, so a film of 0 returns a exactly. The film also glosses: its smooth surface mirrors the light with the Fresnel reflectance of water (n = 1.33; the dry dielectric uses 1.5) in a lobe half as wide as the dry one (Gaussian, sigma 0.03 (1 + 4 roughness) rad for the dry surface), radiance factor pi F G(eps) / cos(light) with eps the angle between the mirrored light and the viewing direction (|light_deg - view_deg| in the plane of incidence, the viewer opposite the light).
albedo in [0, 1] and roughness in [0, 1] broadcast with water_film_um (>= 0); view_deg and light_deg are scalars in [0, 90). The table has wet_albedo, dry_albedo, ratio (wet / dry, 1 where the albedo is 0), film_albedo (the fully wet value), coverage, internal_reflectance_mean (r), fresnel_light (R_s), specular_dry, specular_wet, specular_fraction_dry / specular_fraction_wet (the share of the specular radiance factor in the total), wet_albedo_rgb (shape + (3,), with the index of water at 0.61 / 0.54 / 0.465 um), n_water_rgb, n_water and darker (all wet albedos below the dry ones where the film is thick). Albedos or roughness outside [0, 1], a negative film and angles outside [0, 90) are refused.
Every optics op validates its input before computing (nothing slips through silently):
• Units are baked into the argument name — _mm / _um / _deg / _mrad. Confusing mm with µm does not crash; it yields a plausible-looking wrong answer, so the name prevents it. Nothing here guesses the unit from the magnitude.
• Strings raise ValueError — float('50') succeeds, so an unparsed configuration value would slip through as a length (measured: thin_lens('50', '200') returned a plausible 66.667 mm). bool is refused too, as the implicit promotion True == 1.
• complex / masked arrays raise ValueError (real-valued slots only; silently dropping the imaginary part or peeling off the mask is refused). NaN/Inf raises ValueError on every input.
• Division by zero and its relatives are refused by name: focal length 0, radius of curvature 0, refractive index <= 0, a fully opaque aperture (all zeros, so the normalisation is 0/0), a PSF whose sum is <= 0, a Stokes vector with S0 = 0, and an object sitting at the front focal point (the image is at infinity).
• Only two ops return a non-finite value, and both state it as a contract: depth_of_field returns far_mm = inf beyond the hyperfocal distance (that is what the hyperfocal distance means), and gaussian_beam returns wavefront_radius_mm = inf at the waist (the radius of curvature of a plane wavefront). Both also return a finite companion (far_is_infinite / curvature_per_mm). Any other silent NaN/Inf is detected internally and raises ValueError — "float64 overflowed" and "the answer is infinite" are different claims, so the first is never returned wearing the face of the second.
• Size caps: generated grids are capped by optics.MAX_GRID (4096); supplied fields/PSFs/apertures by optics.MAX_FIELD_ELEMENTS (2^24); ABCD element chains by optics.MAX_SYSTEM_ELEMENTS (1024); Zernike by MAX_ZERNIKE_TERMS (512) / MAX_ZERNIKE_ORDER (40) / MAX_ZERNIKE_BASIS (2^25). This closes, fail-closed, the paths where a small argument triggers a huge internal allocation (measured: n_max=40 × 4096² needs 108 GB).
• Physically impossible states are refused too: a Stokes vector with degree of polarisation > 1, negative transmittance, negative intensity, and invalid Zernike indices such as n-|m| odd.
• 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_water_inspection_images — py -3.11 examples/poc_water_inspection_images.py
table as input)abcd_matrix · wavefront_stats · sfr_from_edge · paraxial_trace · seidel_coefficients · spot_stats · tolerance_analysis · wavefront_from_opd
watervision)caustic_irradiance · bottle_image · fill_level_from_image · wet_dry_inspection_pair · underwater_inspection_image · caustic_floor_segmentation
*Provenance: watervision.py — OPTICS 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.