Data in this section is drawn from CIE Datasets1 with permission of the CIE.
ICC.1 colour management assumes a fixed colorimetric PCS, with a D50 illuminant and CIE 1931 Standard Colorimetric Observer. In ICC.2 the profile creator can choose to apply different illuminants and observers when computing XYZ tristimulus values. For interoperability it is highly desirable that when profiles use such alternative data, the same values are used and that the values correspond directly to those defined by CIE.
Data is provided at 1nm or 5nm intervals, over the range 360-780 for observers and 300-780nm for illuminants (which ensures that any fluorescent excitation is included). Where the range or interval of the observer, illuminant or measurement data do not match, the procedures described in CIE Publication 152, should be followed.
The entries in the CIE Data Page column link to the information on the observer or illuminant on the CIE site, including data description, metadata and citation details. Metadata is available in machine-readable .json files.
| Illuminant or observer | CIE designation | Interval (nm) | CIE data page |
|---|---|---|---|
| Illuminant | CIE standard illuminant D50 | 1 | CIE standard illuminant D50 - 1 nm |
| Illuminant | CIE standard illuminant D65 | 1 | CIE standard illuminant D65 - 1 nm |
| Illuminant | CIE standard illuminant A | 1 | CIE standard illuminant A - 1 nm |
| Observer | CIE 1931 colour matching functions, 2 degree observer | 1 | CIE 1931 observer - 1nm |
| Observer | CIE 1964 colour matching functions, 10 degree observer | 1 | CIE 1964 observer - 1nm |
CIE defines the calculation of colorimetric values at 1 and 5nm intervals2. Many of the measurement instruments in common use in colour management output spectral data at 10nm intervals. Rather than calculate interpolated values for every measurement, it is recommended to use tabulated weighting functions which combine both observer and illuminant.
ISO 136553 includes weighting tables for 10nm data, based on a table published in ASTM E.3084. This combines the D50 illuminant and the CIE 1931 standard colorimetric observer. These tables should be used for ICC.1 and for all cases where compatibility with legacy data is needed.
In ICC.2 the Profile Connection Space can be colorimetric or spectral, and profile connection conditions provide a mechanism to connect data with different observers or illuminants. In an ICC.2 workflow it is also possible to connect colorimetric and spectral data via estimated reflectances.
There are different methods of calculating weighting tables, and work by Li and others, (2016)5 showed that a least-squares method produced the best agreement with tristimulus values calculated with 1nm data.
To support spectral connection in ICC.2, we provide a selection of weighting tables calculated using a least-squares method by Tanzima Habib, a researcher at NTNU, Norway, using the LWL method described by Li and others (2016)5.
| Illuminant | Observer | Range | Interval (nm) | Weighting function |
|---|---|---|---|---|
| D50 | 1931 | 380-780 | 10 | Wts-D50-1931-380-10-780nm.csv |
| D65 | 1931 | 380-780 | 10 | Wts-D65-1931-380-10-780nm.csv |
| A | 1931 | 380-780 | 10 | Wts-A-1931-380-10-780nm.csv |
| LEDB1 | 1931 | 380-780 | 10 | Wts-LED-B1-1931-380-10-780nm.csv |
| F11 | 1931 | 380-780 | 10 | Wts-F11-1931-380-10-780nm.csv |
| D50 | 1964 | 380-780 | 10 | Wts-D50-1964-380-10-780nm.csv |
| D65 | 1964 | 380-780 | 10 | Wts-D65-1964-380-10-780nm.csv |
| A | 1964 | 380-780 | 10 | Wts-A-1964-380-10-780nm.csv |
| LEDB1 | 1964 | 380-780 | 10 | Wts-LED-B1-1964-380-10-780nm.csv |
| F11 | 1964 | 380-780 | 10 | Wts-F11-1964-380-10-780nm.csv |
A CIE Technical Committee6 is currently reviewing methods of calculating XYZ tristimulus values. Feedback on the use of these weighting tables is welcome and should be sent to the ICC Technical Secretary.
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