[argyllcms] Re: Using spotread and xicclu to create a CIECAM02 Jab colour wheel

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 24 Mar 2015 08:29:55 +1100

Hedley Finger wrote:

Hi,

> My task is simple: to record measurements for each colour paint, and
> convert them to colour angle and saturation percentage to plot a colour
> wheel with sample spots as shown at the Handprint site. Graeme Gill kindly
> pointed me to spotread and xicclu as the commands to use. But I'm totally
> bewildered by all the options because I have very little knowledge of
> colour science.
> 
> Some questions to be answered:

>    - Should I calibrate the instrument using the white chip or using the
>    Arches paper on which the samples will be painted, it being the one I use
>    for all my paintings?

The SpectroLino should be calibrated in the usual way. Since you aren't
interested in the L* (or J*) value, I wouldn't worry about normalizing
to the media.

>    - What options should I set for spotread to get the correct output to
>    the log file? (Graeme has advised me how to edit the log file to retain
>    just the data needed.)

It's pretty much as I laid it out. Just because there are a lot of
options, doesn't mean that you have to use them - the general
rule is to assume the defaults will do what you want, unless
proven otherwise.

So literally:

  spotread log.txt

will default to reflective measurement using the Spectrolino,
and follow the prompts to calibrate, then measure your colors.

log.txt will be a text file.

Delete the delete top line and on each line below delete
the index number and the next three numbers (the XYZ value), leaving
just the 3 last numbers on each line.

Locate the lab2lab.icm file (it will be in the 'ref' folder)
and use:

  xicclu -pJ lab2lab.icm < log.txt

to compute JCh values.

You can of course capture the output using re-direction:

  xicclu -pJ lab2lab.icm < log.txt > out.txt

Note that if you are inexperience in using a command line environment,
you will have to come to grips with locating and specifying the file
paths, as well as making sure that the ArgyllCMS executables are
in your $PATH.

A complication on Linux that is noted in the ArgyllCMS installation
instructions is the possible need to alter the serial port permissions
to allow you to access them.

Graeme Gill.


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