Planckian Track Duv Approximation

Approximate signed local CIE1960 uv normal displacement at explicitly supplied reference temperature, positive toward increasing v; not global nearest-locus CCT search or standards-grade Duv far from the reference tangent.

Description

A local Planckian displacement projects measured chromaticity onto a normal at a chosen reference temperature.

A local Planckian displacement projects measured chromaticity onto a normal at a chosen reference temperature. It is an approximation to Duv near that reference.^[1]

Enter physical xy with 0<x,y<1 and x+y≤1 plus temperature 1667–25000 K. Approximate reference xy, convert to CIE 1960 uv and derive a tangent from reference±1 K, clamped to supported endpoints. Orient its normal toward increasing v; return signed projection and reference uv.

When to use Planckian Track Duv Approximation

Use Planckian Track Duv Approximation when you need to evaluate the supplied records under the calculation and evidence rules below. No global nearest-locus CCT search or standards-grade distant Duv is performed.

Prepare colors in the stated color space and scale. Use encoded RGB fractions, linear RGB, Lab, xy, byte values or ink percentages exactly as requested; supply caller tolerances and reference conditions.

How to use Planckian Track Duv Approximation and understand its results

Prepare colors in the stated color space and scale. Use encoded RGB fractions, linear RGB, Lab, xy, byte values or ink percentages exactly as requested; supply caller tolerances and reference conditions.
Enter measuredXy, callerReferenceKelvin using the field table and calculation rules, then run the tool.
Read signedLocalPlanckianDuv, referenceCie1960Uv. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
measuredXy	Measured xy	list of number	Required
callerReferenceKelvin	Caller reference kelvin	number	Required

signedLocalDuv=(measuredUv−referenceUv)·orientedUnitNormal

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
signedLocalPlanckianDuv	Signed local planckian duv	number
referenceCie1960Uv	Reference cie1960 uv	list of number

json

{
  "input": {
    "measuredXy": [
      0.3134941075102412,
      0.32366253911989207
    ],
    "callerReferenceKelvin": 6500
  },
  "output": {
    "signedLocalPlanckianDuv": 0,
    "referenceCie1960Uv": [
      0.20041297662543764,
      0.31037029723937803
    ]
  }
}

Limitations and assumptions

No global nearest-locus CCT search or standards-grade distant Duv is performed.

Numeric inputs, where present, must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Numeric lists are limited to 10,000 entries; string lists to 128 strings of at most 128 characters each. The rules above may impose smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Blackbody Kelvin to xy Chromaticity Approx: A bounded polynomial estimates Planckian-locus xy from blackbody temperature. A measured lamp need not follow that locus. For a complementary task, use White Point D65 Calibration Check: A nominal D65 white check can compare physical xy coordinates in CIE 1960 uv. Chromaticity proximity is one calibration measurement.

References

Planckian Track Duv Approximation — tool.io

Similar or alternative tools

Blackbody Kelvin to xy Chromaticity Approx
A bounded polynomial estimates Planckian-locus xy from blackbody temperature. A measured lamp need not follow that locus.
White Point D65 Calibration Check
A nominal D65 white check can compare physical xy coordinates in CIE 1960 uv. Chromaticity proximity is one calibration measurement.