Making connections with iccMAX
A guide to understanding how profile connection works using iccMAX profiles
iccMAX profile connection Connecting with iccMAX
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PCS Conversion and/or Adjustment
Transform type selection with iccMAX profiles establishes both the transform tag as well as the associated PCS configuration (associated with colour space encoding, illuminant, observer, and spectral ranges as they apply) that will be used for the profile connection within the CMM. Once PCS configurations are established for both the source and destination profiles, the PCS operations are generally the same as PCS operation with V2/V4 profiles (though with more options and details involved). The CMM applies the transform of the profile going into the PCS (source profile) performs PCS adjustments (as needed), and then applies the transform of the profile going out of the PCS (destination profile). And, PCS adjustment in the middle by the CMM generally involves the same operations as for V2/V4 profiles:- Pass-through (No change) - This happens when the PCS configuration of the source profile transform directly matches the PCS configuration of the destination profile transform (and no further CMM controls are applied).
- Colour configuration conversion - This happens when the source and destination profiles do not have the same PCS configuration. There are two aspects of PCS configuration conversion that apply with iccMAX based PCS connection: Colour space conversion and observing condition conversion.
- Colour space conversion - PCS connection with iccMAX profiles can performed with spectrally-based colour spaces (in terms of reflectance, transmittance, emission, or fluorescence) in addition to colorimetric XYZ and CIELAB colour spaces. (Note: Annex A in the iccMAX specification defines all valid inter PCS connections and the operations involved in their conversion). For example: When a spectral PCS is connected to a colorimetric PCS then observer and illuminant information from the profile connection conditions is applied to convert to colorimetry (which requires application of both an illuminant and colour matching functions of an observer). The profile connection conditions that define the illuminant and observer that are to be used may be obtained either from the profile (in the spectral viewing conditions tag, which is required) or provided as a CMM control option external to the profile.
- Observing condition conversion - Conversions are applied by a CMM when the illuminant and/or colorimetric observer do not match between the source PCS and the destination PCS.
The conversion transforms between custom observing conditions and standard observing conditions (for the 1931 standard 2-degree observer under a D50 illuminant) are encoded as required tags in an iccMAX profile whenever it has a colorimetric PCS with custom observing conditions or a spectral PCS. These tags are required for the CMM to be able to make one of the following three observing condition conversions:
- Custom-to-standard conversion applied for the source profile
- Standard-to-custom conversion applied for the destination profile
- Custom-to-standard conversion applied for the source profiled followed by the standard-to-custom conversion applied for the destination profile
(Note: In some cases, a CMM may be provided with control options by the application that provide overrides of the PCC tags used for observing condition conversion).
- An additional colour space conversion may be performed when a V2 profile and an iccMAX profile are connected using the same adjustment that is performed for the perceptual intent between V2 and V4 profiles.
- Colour space conversion - PCS connection with iccMAX profiles can performed with spectrally-based colour spaces (in terms of reflectance, transmittance, emission, or fluorescence) in addition to colorimetric XYZ and CIELAB colour spaces. (Note: Annex A in the iccMAX specification defines all valid inter PCS connections and the operations involved in their conversion). For example: When a spectral PCS is connected to a colorimetric PCS then observer and illuminant information from the profile connection conditions is applied to convert to colorimetry (which requires application of both an illuminant and colour matching functions of an observer). The profile connection conditions that define the illuminant and observer that are to be used may be obtained either from the profile (in the spectral viewing conditions tag, which is required) or provided as a CMM control option external to the profile.
- Rendering intent adjustment - iccMAX profiles can encode transform tags for either absolute or relative intent. When one is not present then absolute/relative adjustments are performed to achieve the missing rendering intent transformation. PCS adjustment in XYZ is performed for colorimetric PCS connection and spectral PCS adjustment relative to the spectralWhitePointTag is performed for spectral PCS connection in similar fashion to absolute/relative processing performed by V2/V4 CMMs.
- CMM controlled adjustment - An iccMAX capable CMM might have a control option (requested by the calling application) that causes the CMM to perform additional PCS adjustments. In addition to Black Point Compensation for colorimetric PCS connection, a CMM might be instructed to perform luminance matching. This uses the luminances of the illuminants in the connecting profiles to linearly scale the XYZ colorimetry, thus providing a match of the luminances.