PhysLight Explorer: カメラ分光感度

インタラクティブPhysLight：blackbody・LED・HMI・レーザーのスペクトルを実測カメラR/G/B曲線に重ね、センサー比較とメタメリズムを確認。合わせて使う CIE 1931, Display Check, とレッスン. Spectral curves from the open PhysLight project — thanks to Wētā (Wētā Digital / Wētā FX), Apache-2.0.

PhysLight Explorer

Lightsaber data

Drop a spectrum on a real camera's measured R/G/B sensitivities. Same light, different sensors — that's metamerism.

Daylight WB

Raw response

Camera A

Camera B (compare)

Light source

Planck SPD · drag Kelvin

Colour temperature

5600 K

3200

5600

6500

10k

Canon EOS R5

WB linear RGB

1.00

0.83

0.68

1.000, 0.832, 0.684

Sony ILCE-7SM3

WB linear RGB

1.00

0.86

0.71

1.000, 0.855, 0.709

Human (CIE 1931)

What a standard observer would report as the colour of this SPD — cameras rarely match this exactly.

Nested squares like PhysLight's chart: outer = base response, inset = compare. Same patch / same light — colour shifts are metamerism (or camera vs CIE).

Outer · Cam A · EOS R5Inset · Cam B · ILCE-7SM3

Export matrix & 3D LUT

.nk

.cube

Least-squares 3×3 from Camera A RGB → target on the 24 ColorChecker patches under the current illuminant. Per-patch Δ shows where a linear map fails; the optional .cube adds an IDW residual so on-chart colours land closer than matrix alone. Educational — not a lab camera profile.

Cam A → CIE XYZ

Cam A → Cam B

0.5914  0.0371  0.1577
0.2339  0.8134  -0.2338
0.0475  -0.3003  1.3613

Mean rel residual: 1.6% · worst: 5.6% · EOS R5 → CIE XYZ (rel. Y) · 5600 K blackbody

Per-patch residual (after 3×3)

Worst first

Chart order

Heatmap = relative error % on each ColorChecker patch (darker / redder = larger linear-fit miss).

#	Patch	Rel %	\|Δ\| mean	ΔR	ΔG	ΔB
16	Red	5.6	0.0137	-0.0145	-0.0124	-0.0141
19	Cyan	4.0	0.0159	-0.0124	-0.0155	-0.0198
14	Blue	3.1	0.0092	+0.0076	+0.0085	+0.0116
7	Bluish green	2.8	0.0135	-0.0111	-0.0129	-0.0165
11	Purple	2.6	0.0039	+0.0016	+0.0040	+0.0061
3	Light skin	2.3	0.0105	-0.0081	-0.0104	-0.0131
10	Moderate red	2.2	0.0073	-0.0051	-0.0071	-0.0098
9	Purplish blue	2.0	0.0076	+0.0058	+0.0070	+0.0099
13	Orange yellow	1.7	0.0092	+0.0093	+0.0087	+0.0095
4	Blue sky	1.6	0.0054	+0.0049	+0.0051	+0.0063
5	Foliage	1.4	0.0020	+0.0005	+0.0022	+0.0033
18	Magenta	1.2	0.0043	-0.0070	-0.0035	-0.0025
24	Neutral 3.5	1.0	0.0010	+0.0009	+0.0009	+0.0013
25	Black	1.0	0.0004	+0.0003	+0.0003	+0.0005
8	Orange	0.9	0.0039	+0.0055	+0.0032	+0.0031
23	Neutral 5	0.9	0.0020	+0.0019	+0.0018	+0.0024
22	Neutral 6.5	0.9	0.0035	+0.0033	+0.0031	+0.0039
15	Green	0.9	0.0022	-0.0018	+0.0016	+0.0034
21	Neutral 8	0.8	0.0050	+0.0049	+0.0048	+0.0053
2	Dark skin	0.7	0.0010	-0.0011	-0.0010	-0.0008
12	Yellow green	0.5	0.0025	-0.0015	+0.0018	+0.0043
20	White	0.5	0.0051	+0.0055	+0.0052	+0.0047
6	Blue flower	0.2	0.0010	-0.0010	+0.0003	+0.0018
17	Yellow	0.2	0.0014	-0.0016	-0.0016	-0.0009

Preview Nuke script

# PhysLight Explorer → Nuke ColorMatrix
# Educational fit from measured camera spectral sensitivities × ColorChecker reflectances.
# Not a production camera profile. Validate before use.
# Fit under 5600 K blackbody; daylight-WB camera RGB → CIE XYZ (rel. Y); ColorChecker Classic (Ohta 1997) 24 patches
ColorMatrix {
 matrix {
		{ 0.59141067 0.03706286 0.15765617 }
		{ 0.23390597 0.81338272 -0.23382498 }
		{ 0.04753048 -0.30033174 1.36129747 }
 }
 name PhysLight_Canon_EOS_R5_to_XYZ
 label "EOS R5 → CIE XYZ (rel. Y) · 5600 K blackbody"
}

3D LUT (.cube)

17³

Adobe/IRIDAS lattice (R varies fastest). Domain covers the fit samples (0 → max src). Residual mode is tighter on the chart; matrix-only is an exact linear bake of the 3×3.

Matrix + residual

Matrix only

17³

33³

Preview .cube header (PhysLight_Canon_EOS_R5_to_XYZ_mat+res_17.cube)

# PhysLight Explorer → 3D LUT (.cube)
# Educational fit from measured camera spectral sensitivities × ColorChecker.
# Not a production camera profile. Validate before use.
# Order: red varies fastest (Adobe/IRIDAS).
# Fit under 5600 K blackbody; daylight-WB camera RGB → CIE XYZ (rel. Y); ColorChecker Classic (Ohta 1997) 24 patches
# Lattice = 3x3 matrix + IDW residual (fades to matrix off-chart).
# LUT_3D_SIZE 17
TITLE "PhysLight_Canon_EOS_R5_to_XYZ_mat+res_17"
DOMAIN_MIN 0.00000000 0.00000000 0.00000000
DOMAIN_MAX 1.43082121 1.43082121 1.43082121
LUT_3D_SIZE 17
0.00032601 0.00074218 0.00122484
…
# 4913 lattice lines omitted

Thanks to Wētā(Wētā Digital / Wētā FX) for measuring these camera spectral curves with the PhysLight “lightsaber” and releasing them open source. Source: github.com/wetadigital/physlight (data/camera), Apache License 2.0. ColorChecker spectra: Ohta (1997) / ISO 17321-1. Curves are repackaged for this tool; see bundled LICENSE/ATTRIBUTION in the repo. Explorer UI © CompStart — educational use, not colour-critical production. AS IS, no warranty.