GIFSQ Tools · Module 2 — Food Chemistry & Physicochemical Testing · Tool 34 of 500
Enter CIE L*a*b* readings from a colour instrument and get chroma, hue angle and the colour quadrant.
Try sample values — fills the form with the worked example below.
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Chroma C*
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Hue angle h°
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Lightness L*
Equation: Chroma C* = √(a*² + b*²). Hue angle h° = atan2(b*, a*) in degrees, adjusted to 0–360°. L* runs 0 (black) to 100 (white); a* is negative toward green and positive toward red; b* is negative toward blue and positive toward yellow.
Method: CIE L*a*b* colour space, CIE 15 / ISO 11664-4 — instrument readings under a stated illuminant and observer (commonly D65 / 10°); chroma and hue are derived from a* and b* as defined by the CIE.
Assumptions: the readings come from a calibrated instrument with the illuminant and observer recorded; a* and b* are on the CIE scale.
Limitations: hue angle has no meaning when chroma is 0 (a grey — the tool reports 0°); L*a*b* values from different illuminants or observers are not directly comparable; the space is not fully uniform, so equal steps do not always look equal.
Rounding: chroma and hue angle to 2 decimal places, L* to 2 decimal places; intermediate values are not rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: CIE L*a*b* colour space, CIE 15 / ISO 11664-4 — instrument readings under a stated illuminant and observer (commonly D65 / 10°); chroma and hue are derived from a* and b* as defined by the CIE.
Assumptions: the readings come from a calibrated instrument with the illuminant and observer recorded; a* and b* are on the CIE scale.
Limitations: hue angle has no meaning when chroma is 0 (a grey — the tool reports 0°); L*a*b* values from different illuminants or observers are not directly comparable; the space is not fully uniform, so equal steps do not always look equal.
Rounding: chroma and hue angle to 2 decimal places, L* to 2 decimal places; intermediate values are not rounded.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: A sample reads L* 50.00, a* 30.00, b* 40.00. Chroma = √(30² + 40²) = √2500 = 50.00; hue = atan2(40, 30) = 53.13°, in the red-yellow quadrant.
Enter values above to see results.
Hue quadrants: 0° red, 90° yellow, 180° green, 270° blue. Record the illuminant (D65) and observer (10°) with every L*a*b* set. Tool 34 of 500 — GIFSQ
