Colour Calibration using Linux and GIMP
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The goal is to aid the viewer to see the image on the viewer's monitor
in a way that mimics the intensities and colours that the image-maker
intended.  Although this is somewhat inaccurate, the following
instructions should make a difference.

The Monitor:

1) Do not use flourescent lighting. Work in daylight or darkness.

2) Settings on Monitor:

     Temperature = 6500K
     Contrast = 100%
     Brightness ~ 50%
     
3) Calibrate the Gamma:
    Use the calibration image files at
    http://www.physics.umanitioba.ca/~english/vis2009  
             Gamma_black_new.png
             malingreyscale.jpg 

   Ensure gamma = 2.2 visually, in the following way.

   a) View Gamma_black_new.png.

   b) Using the command line iteratively type
          xgamma -gamma f.f
      where f.f equals numbers like 1.5 or 1.2, etc.

   c) Repeat b) until the chart on the left of Gamma_black_new.png
      appears to have the same value of grey horizontally at the 
      level of 2.2, rather than appearing as distinct columns.  
      It helps to sit away from the chart and defocus your eyes. 

   d) Simultaneously check that the chart on the right.  At the 
      2.2 level, Column A should become just visible from its surroundings
      as it goes from black (at top) to grey (on bottom) AND Column B should
      be distinguishable from the surrounding columns.

   e) Check the balance of white and greys and hues in  malingreyscale.jpg.
      The greys should be neutral (e.g. not bluish) and the whites should
      be pure  (e.g. not bluish).

Comparisons between the electronic and printed images:
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Do not use flourescent lighting. Work in daylight. That is, let
daylight fall on the prints, but block excess light from hitting the
monitor.

The above monitor versions should compare favourably with 
printouts.  The accuracy is about 20% for the colour.