Pearl Luster Grade Rater

Measure unique specular highlight FWHM from observed calibrated profile and background, not total specular share or a universal pearl-luster grade; missing/multiple half-height crossings are not invented.

Description

Pearl luster relates to the strength and sharpness of reflected highlights.

Pearl luster relates to the strength and sharpness of reflected highlights. A measured highlight profile offers a quantitative width proxy under declared imaging conditions.^{[1, 2]}

When to use Pearl Luster Grade Rater

Use this tool to measure unique specular highlight FWHM from observed calibrated profile and background, not total specular share or a universal pearl-luster grade; missing/multiple half-height crossings are not invented.

Prepare the gemstone measurements, spectra or comparison data and any supplied calibration parameters. Check units, reference conditions and record alignment.

How to use Pearl Luster Grade Rater and understand its results

Prepare the gemstone measurements, spectra or comparison data and any supplied calibration parameters. Check units, reference conditions and record alignment.
Enter profileOffsetsMm, measuredSpecularProfile, backgroundSignal using the field table and calculation rules, then run the tool.
Read observedSpecularFwhmMm, backgroundCorrectedPeakSignal. 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
profileOffsetsMm	Profile offsets mm	list of number	Required
measuredSpecularProfile	Measured specular profile	list of number	Required
backgroundSignal	Background signal	number	Required

Pair nonnegative profile signals with increasing mm offsets and subtract nonnegative background. Require a unique positive interior peak and exactly one half-height crossing on each side, interpolated linearly. Return full width at half maximum and corrected peak signal.

Paired lists must be nonempty and have equal lengths. Each sequence checked for increasing order must contain at least two strictly increasing values.

FWHM=right half-maximum crossing−left half-maximum crossing

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

Output field	Meaning	Value type
observedSpecularFwhmMm	Observed specular fwhm mm	number
backgroundCorrectedPeakSignal	Background corrected peak signal	number

json

{
  "input": {
    "profileOffsetsMm": [
      -2,
      -1,
      0,
      1,
      2
    ],
    "measuredSpecularProfile": [
      0,
      1,
      2,
      1,
      0
    ],
    "backgroundSignal": 0
  },
  "output": {
    "observedSpecularFwhmMm": 2,
    "backgroundCorrectedPeakSignal": 2
  }
}

Limitations and assumptions

Missing, multiple or plateau crossings are rejected. Imaging conditions remain supplied; the result is not a universal pearl-luster grade.

Numeric inputs and returned numeric values must be finite; an unrepresentable returned value produces an error. Numeric lists are limited to 100,000 entries; the rules above may require smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors.

Alternative or Complementary methods

Use Lustre Reflectivity Ratio: Audit measured specular/total reflected signal with independently supplied background and angular exposure, retaining signed overcorrection; not absolute reflectance, Fresnel theory or validated lustre grading. For a complementary task, use Scintillation Pattern Index: Integrate measured temporal brightness variation under piecewise-linear frames, retaining actual exposure; scalar scintillation proxy is not complete observer-dependent sparkle or commercial grade.

Further background: Pearl quality factors.

References

Pearl Luster Grade Rater — tool.io
Pearl quality factors — Gemological Institute of America

Similar or alternative tools

Lustre Reflectivity Ratio
Audit measured specular/total reflected signal with independently supplied background and angular exposure, retaining signed overcorrection; not absolute reflectance, Fresnel theory or validated lustre grading.
Scintillation Pattern Index
Integrate measured temporal brightness variation under piecewise-linear frames, retaining actual exposure; scalar scintillation proxy is not complete observer-dependent sparkle or commercial grade.