Setting an environment variable

Environment variables

This overrides the default 3D visualisation file format for tools such as iccgamut or viewgam. Set to VRML or X3D or X3DOM, which will result in .wrl, .x3d and .x3d.html files respectively. See 3d Viewing Format.

Normally the display technology type determines how long is allowed between when a patch color change appears on the display, and when that change has settled down, and as actually complete within measurement tolerance. A CRT or Plasma display for instance, can have quite a long settling delay due to the decay characteristics of the phosphor used, while an LCD can also have a noticeable settling delay due to the liquid crystal response time and any response time enhancement circuitry. [ Instruments without a display technology type selection such as spectrometers assume a worst case.].
The ARGYLL_DISPLAY_SETTLE_TIME_MULT environment variable allows the rise and fall times of the model to be scaled to extend or reduce the settling time. For instance, ARGYLL_DISPLAY_SETTLE_TIME_MULT=2.0 would double the settling time, while ARGYLL_DISPLAY_SETTLE_TIME_MULT=0.5 would halve it.

By default ArgyllCMS uses the Bradford sharpened cone Chromatic adaption matrix in adapting the measured, absolute colorimetric test data to the PCS (Profile Connection Space) relative colorimetric D50 white point for all profile types. This makes the profile handling consistent with the widely deployed (HP & Microsoft) sRGB and AdobeRGB profiles, as well as being recommended practice in modelling chromatic adaption.  The ICC profile format though, specifies the use of a non-cone space XYZ adaptation (so called "Wrong Von Kries" chromatic adaptation) [ ICC Specification ICC.1:2001-04 (ICCV2.4) Annex A, pp 66, equations A.1, A.2 & A.3 ], so ArgyllCMS profiles have a very slight incompatibility with ICC profiles created strictly according to the ICC specifications, depending on how close to white Output (i.e. print) profiles media white is to the perfect diffuser. (Note that CMM's that strictly follow the ICC specifications have much more gross incompatibilities due to this, when dealing with the HP & Microsoft sRGB and AdobeRGB profiles.) By setting this environment variable, Output (i.e. print) profiles will be created that better conform to the ICC specification, and  therefore have better inter-interoperability with some other CMMs, at the cost of poorer color behavior.
See also the ArgyllCMS 'arts' tag.

The ICC V2 format originally provided no clear mechanism for Display profiles to use a modern chromatic adaptation transform in dealing with the D65 white point of typical displays. Profile makers ended up taking two different approaches :- one was to use a Bradford chromatic transform for the media (display) white to PCS D50 (this approach being used by the widely deployed HP & Microsoft sRGB and AdobeRGB profiles, as well as ArgyllCMS profiles by default), and the other was to apply the Bradford transform to the measurement data and then disable Absolute Intent for display profiles by setting the mediaWhitePoint tag to D50. The latter approach was supplemented later on with the introduction of the ChromaticAdapation ('chad') tag, but this did not restore the Absolute Colorimetric capability to Display profiles. The latter approach has also been adopted more formally in the ICC V4 specifications. To restore the Absolute Intent for such profiles, ArgyllCMS will make use of the 'chad' tag in such profiles when Absolute Colorimetric intent is requested, but by default does not create such profiles. Setting this environment variable causes it to create Display profiles in the fashion dictated by the ICC V4 spec. :- setting the mediaWhitePoint tag to D50 and storing the display media white to D50 matrix in the 'chad' tag. (This approach has slightly poorer accuracy for Absolute Intent than ArgyllCMS's default.)

For Output type devices (i.e. Printers), the assumption is that test patches are measured under D50 illuminant. It can be very useful for proofing to calculate color corrections for other, real world illuminants, and ArgyllCMS makes provision for this with the coloprof -i parameter, or the spec2cie -i parameter. To be broadly useful, this change in illuminant needs to be available to CMM's, which the ArgyllCMS's implementation makes possible by incorporating the illuminant change into the absolute XYZ values and hence the white point tag, so that Absolute Colorimetric rendering intent returns XYZ values under that illuminant using any CMM.

The ICC specification have provision for hiding this difference in illuminant by chromatically transforming the absolute values to be functionally equivalent to having been measured using a D50 illuminant, and recording this transform in the ChromaticAdapation ('chad') tag. This appears to motivated by the assumption that the difference in illuminant is a quirk or limitation of the instrument that is to be worked around, as well as the limitation of the ICC Absolute to Relative chromatic transformation being based on the inferior non-cone space XYZ adaptation (so called "Wrong Von Kries" chromatic adaptation), while the ChromaticAdapation tag allows for the use of a superior cone-space based transformation. (see ARGYLL_CREATE_WRONG_VON_KRIES_OUTPUT_CLASS_REL_WP above for more details.)

To allow for strict conformance to the ICC specification when using non-standard illuminants, setting the ARGYLL_CREATE_OUTPUT_PROFILE_WITH_CHAD environment variable causes a non-D50 illuminant white point change to be hidden in the ChromaticAdapation Tag, and to still allow this to be useful in a proofing situation, ArgyllCMS will incorporate the effect of the ChromaticAdapation Tag when Absolute Colorimetric Intent is chosen. Note that other CMM's may not do so. For full conformance with ICC specifications, the ARGYLL_CREATE_WRONG_VON_KRIES_OUTPUT_CLASS_REL_WP variable would also be set, but neither of these options is recommended, since ArgyllCMS's default behavior will give superior results.

By default the ChromeCast test patch source uses a special receiver application that gets the test patch data directly. By setting this environment variable to true, the default Google ChromeCast receiver will be used, making use of a local web server to provide the images. This is slower than the special reciever, but can be used as a fallback.

By default ArgyllCMS >= V 1.9.4  will use its native ucmm to store display ICC profiles on Linux based systems, but if the ARGYLL_USE_COLORD environment variable is set, it will attempt to use the Gnome colord storage instead.

Normally ArgyllCMS will try and identify any device on a fast serial port (i.e. USB or BlueTooth based port). This may disturb devices it doesn't know about, so the ARGYLL_EXCLUDE_SERIAL_SCAN variable can be set to a semi-colon or comma separated list of serial ports that should not be fast scanned. Example:

"COM2;/dev/tty5" etc.

If the ARGYLL_XRGA  environment variable is set to:

    XRGA, then all Getag-MacBeth/X-Rite reflective measurements will be converted to XRGA.
    XRDI, then all Getag-MacBeth/X-Rite reflective measurements will be converted to XRDI.
    GMDI, then all Getag-MacBeth/X-Rite reflective measurements will be converted to GMDI.

If not set (or set to some other string), then the native calibration will be used. Note that the values must be upper case.

Whenever a color device profile value is inverted (i.e. in creating ICC B2A tables, or creating a device link using gamut mapping mode), colors that are out of gamut after gamut mapping, will be clipped to the gamut surface. If the device behavior is poor (i.e. non-monotonic), the gamut surface representation used for clipping may have "shadow" areas that result in non-smooth jumps in clipped output. Setting the ARGYLL_UNTWIST_GAMUT_SURFACE environment variable to a non empty value will invoke an additional step in the gamut surface creation routine, that attempts to minimize such shadowed surface areas. This can improve the smoothness of clipped colors for poorly behaved devices, but may make the output for some devices worse.