iccMAX sRGB D65 profiles

The iccMAX specification makes it possible to use a Profile Connection Space other than D50, and hence to avoid the need to apply chromatic adaptation when the data encoding source has an illuminant different from the D50 PCS.

A number of iccMAX profiles for sRGB are available on this page.

iccMAX D65 colorimetric
The iccMAX sRGB_D65_colorimetric profile is built according to the sRGB definition in the sRGB page in the ICC 3-component colour encoding registry, using 32-bit float precision for the transform matrix and curve parameters.

XML mark-up for the profile is also available here.

The profile can be used to obtain D65 XYZ values directly from sRGB data, using the RefIccMax tool ApplyNamedCMM. It can also be used as a reference profile for the sRGB colour space by iccMAX implementations that support the 'ColourEncodingSpace' class of profile.

When used to connect to other another iccMAX profile, if the second profile has a D65 PCS the D65 XYZ data will be exchanged directly. If the connecting profile does not have a D65 PCS, the the PCS data is converted to the standard D50 PCS using the transform in the customToStandardPccTag ('c2sp'). In this profile the 'c2sp' transform is a chromatic adaptation matrix generated using the linearized Bradford transform described in Annex E.3 of ISO 15076-1. In the inverse direction D50 PCS data is converted to the D65 XYZ of this profile using the standardToCustomPccTag ('s2cp') inverse chromatic adaptation matrix.

When connecting to a v2 or v4 profile, the 'c2sp' or 's2cp' tag is always used.

NOTE: The PCS XYZ media white point and illuminant white point values in this profile are [0.9504, 1.0000, 1.0889], as defined in CIE.15 Table 3 and as computed from the 8-bit sRGB encoding maximum of [255, 255, 255] using the transform in this profile. The spectralViewingConditions ('svcn') tag includes values from CIE.15 Tables 1 and 4 for the D65 illuminant and colorimetric observer respectively for the range 380-780nm at 5nm intervals. The illuminant XYZ and surround XYZ values computed from these data, and encoded in the 'svcn' tag, differ slightly from the PCSXYZ values for D65 encoded as media white and illuminant.

Gamut boundary
The iccMAX sRGB D65 colorimetric profile includes an iccMAX gamutBoundaryDescType which defines the gamut of the profile in terms of a list of points on the gamut surface (vertices) and indices into the vertex list defining the set of triangular faces which connect to form the gamut surface. The vertices are D65 XYZ values, computed using the same transform as the profile.

Material Adjustment Transform
The 'c2sp' tag in the iccMAX sRGB D65 colorimetric profile is a chromatic adaptation transform (CAT) which aims to predict the appearance of the colour defined under a D65 illuminant when viewed under the D50 illuminant of the standard ICC PCS. An alternative to chromatic adaptation is a 'Material adjustment transform', which aims to predict the colorimetry of the original if the illumination had been D50 instead of D65. The iccMAX sRGB_D65_MAT.icc profile transforms sRGB to D65 colorimetry in the same way as the iccMAX sRGB D65 colorimetric profile, but when used to convert to the D50 PCS the MAT transform is used instead of the CAT.

Xml mark-up for the iccMAX sRGB D65 MAT profile is available here.

Further details of the MAT transform are described in Derhak (2015).

Colour space encoding
The iccMAX specification includes the Colour Space Encoding class of profiles ('cenc'), which permits a profile to contain a reference to a colour encoding name rather than a transform between a colour encoding and a Profile Connection Space. In the sRGB_ISO22028.icc profile, the referenceName tag is set to ISO22028-1, indicating that the encoding is defined according to ISO 22028-1, and given in full in the colorEncodingParams tag structure 'cept'. The xml mark-up for this profile is here.

A batch file which performs some tests on the above profiles is available, together with supporting data files here. The D50_XYZ.icc and sRGB2014.icc profiles used in these tests can be downloaded from the Profiles page.

Colour vision deficiency
Example iccMAX DeviceLink profiles which transform from sRGB values to XYZ to a modifed XYZ representing the information loss experienced by a dichromat, and back to sRGB, are available here. These profiles are described in Green (2016).

References
M. W. Derhak and R. S. Berns, (2015), Introducing Wpt (Waypoint): A color equivalency representation for defining a material adjustment transform. Color Res. Appl., 40: 535-549

A brief overview of Wpt Normalization and links to MatLab/Octave code and an Excel spreadsheet can be found here.

P. Green and N. Nussbaum, (2016) Colour vision deficiency transforms using ICC profiles, Proceedings of Color Imaging XXI: Displaying, Processing, Hardcopy, and Applications, SPIE 2016.