Description of the .cal format

Device calibration information. This is ASCII text, CGATS, Argyll specific format, used to hold a description of device setup information that brings it to a desired calibration state. Currently only display output curves are defined. Created by dispcal.

While fully compatible with the CGATS.5 Data Exchange Format, the particular required keywords and fields are unique to Argyll, hence an Argyll specific file identifier CAL is used to avoid confusion with standard ANSI or CGATS files.

The .cal format changes from time to time with new releases, to add new functionality, but generally retains backwards compatibility. Note that in the description below, the word "may" indicates an optional component, while the word "shall" indicates a necessary component.

Generally a .cal file contains only one table, the table containing the setup information.


The table contains the following:

The file identifier (First 7 characters) shall be CAL.

A # character introduces a comment.

There may be DESCRIPTOR, ORIGINATOR, or CREATED keywords and values (as per CGATS).

There shall be a DEVICE_CLASS keyword that has a value of "OUTPUT", "DISPLAY" or "INPUT".
This indicates what type of device the calibration information is suitable for.

The NUMBER_OF_FIELDS keyword shall have a value that indicates the number of fields in each data set, e.g. 4 (as per CGATS).

The start of the declaration of the fields shall be marked by the BEGIN_DATA_FORMAT keyword (as per CGATS).

For a DISPLAY device, the following fields shall be used:

    RGB_I       index of the RAMDAC entry.
    RGB_R      RAMDAC Red value for that entry.
    RGB_G      RAMDAC Green value for that entry.
    RGB_B      RAMDAC Blue value for that entry.

The definition of the fields shall be terminated by the END_DATA_FORMAT keyword (as per CGATS).

The NUMBER_OF_SETS keyword shall have a value that indicates the number of sets of data, e.g. 256 (as per CGATS).

The start of the values of the data sets shall be marked by the BEGIN_DATA keyword (as per CGATS).

Each set of data shall be on one line, and shall be separated by white space. All values shall be normalized to lie between 0.0 and 1.0.

The end of the values of the data sets shall be marked by the END_DATA keyword (as per CGATS).

Generally any other keywords and values will be ignored.