Color Difference Formulas
Color difference has a lot of different formulas that quantify the color difference in various ways.
∆E
The most common is ∆E which can be expressed with numbers calculated using various formulas:
- ∆E 1976
- ∆E 1994
- ∆E 1994 for textiles
- ∆E CMC (1:1)
- ∆E CMC (2:1)
- ∆E 2000 (currently recommended for the print industry)
None of those single-number formulas is perfect - in most cases, the observer's impression doesn't correlate perfectly with the numbers - in some situations covered color range seems to be different depending on the direction of color variations.
Other common deltas:
- ∆C - saturation difference
- ∆h - hue angle difference - don't apply on neutral or near neutral colors
- ∆H - hue difference (linear distance in a*b* plane)
- ∆L - lightness difference
- ∆a - linear difference on the magenta-green axis
- ∆b - linear difference on the yellow-blue axis
- ∆Ch -
Multi-axes (Snowflake) Tolerances
This alternate solution is based on tolerances defined for six directions (3-axes). As no one perfect ∆E formula can be easily adopted solution is based on more - than one number, which brings more flexibility in some cases.
Other important metrics
Some phenomena ( Metamerism or Fluorescence) can be hard to control when lighting conditions are different than standardized. Invisible UV components can dramatically change how the sample is perceived. Due to different pigmentations/colorants/dyes, two samples might match in one Illuminant and be dramatically different under another.
The following variables can help solve those potential problems:
- OBA Index (∆bM1-M2) — reflects the amount of Optical Brightening Agents
Note: if this index is higher than 1-2, an M1 M-condition should be used! - Fluorescent Index —
- Metamerism Index —
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