Description of the .cal format
Device calibration information. This is ASCII text, CGATS, Argyll specific format,
to hold a description of device setup information that brings it to
desired calibration state. Calibration files are created by synthcal, dispcal
While fully compatible with the CGATS.5 Data Exchange Format, the
particular required keywords and fields are unique to Argyll, hence
Argyll specific file identifier CAL
is used to avoid confusion with standard ANSI or CGATS files.
The .cal format changes
time to time with new releases, to add new functionality, but
retains backwards compatibility. Note that in the description below,
the word "may" indicates an optional component, while the word
indicates a necessary component.
Generally a .cal file contains only one table, the table containing
The table contains the following:
The file identifier (First 7 characters) shall be CAL.
A # character introduces a
There may be DESCRIPTOR, ORIGINATOR, or CREATED keywords and values (as
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
A "DISPLAY" type device may
have a VIDEO_LUT_CALIBRATION_POSSIBLE
must have a value of "NO" or
"YES", to indicate whether
the display has the ability to be calibrated by loading VideoLUT
There shall be a keyword COLOR_REP
that has a value that indicates what colorspaces of the device
The colorspaces shall be encoded with one or two letters
component. The device spaces shall use the
following letter encoding:
Light Light Black 1k
There may be an a prefix i
preceding the device space letter encoding, indicating that although
the space appears to be an additive space, it is in fact a
Typical values might be: "RGB" for an RGB display, "iRGB"
for an RGB printer, "CMYK"
printer, "RGB" for an RGB
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
The fields shall use the standard CGATS pattern of the full
identified followed by the individual colorant identifier. There
be an initial input index value identified by the letter I.
For an RGB device, the
following fields would be used:
The device value input value between 0.0 and 1.0.
The Red device value input value between 0.0 and 1.0.
The Green device value input value between 0.0
The Blue device value input value between 0.0
The corresponding field names for a CMYK device would be CMYK_I, CMYK_C, CMYK_M, CMYK_Y and CMYK_K, etc.
The definition of the fields shall be terminated by the END_DATA_FORMAT keyword (as per
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
Each set of data shall be on one line, and shall be separated by
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).
There may then be device type specific extra tables that hold target
device behavior information. These will be specific to the tool that
creates that particular type of calibration.
Generally any other keywords and values will be ignored.