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 RALCOLOUR_MATCH(9)                                       RALCOLOUR_MATCH(9)
                                 xx March 93



 NAME
      ralcolour_match - this is not a program, this is a set of instructions
      for the VDU to printer colour matching procedure.

 ORIGIN
      Rutherford Appleton Laboratory

 AVAILABILITY
      The source code of this set of programs together with information on
      how to install them is available from the University of Kent.

 DESCRIPTION
      ralcolour_match is a set of programs and files used in the VDU to
      printer colour matching procedure. This procedure is meant for users
      who have Colour PostScript printers (running PostScript level 1 with
      colour extensions) and want to enhance the quality of their hardcopy
      output. This procedure gives a cheap and easy to use solution to the
      problem, but does not attempt to give an absolute and general
      solution.

      This manual page describes the whole procedure and the format of files
      containing data collected by taking measurements.  The description on
      how to use the relevant programs of this procedure is given separately
      and can be obtained by referring to the appropriate manual page.

      The colour matching procedure consists of three stages:
           - gray balance and contrast adjustment,
           - incorporation of the suplementary black printer, and
           - saturation improvement and colour correction.

      The first two stages involve printing relevant images, taking some
      measurements, storing measurement tables into a file, running programs
      that produce colour matching tables and justifying achieved results.
      This version of software implements only the first stage of the whole
      procedure. The other two stages will be supported in the next release.

      ralcolour_match consists of  programs:

      ralmatch
           - command line version of the filtering program

      ralmatchx
           - Motif version of the filtering program

      16shades
           - the monitor calibration program

      midtone
           - the program used to measure values of Red, Green and Yellow
           colours needed to produce monitor's midtone (midtone is the gray
           colour consisting of 50% of black and 50% of white pigment)



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 RALCOLOUR_MATCH(9)                                       RALCOLOUR_MATCH(9)
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      charts.ps
           - PostScript program for printing colour charts

      black.ps
           - PostScript program for printing a black square

      ralcol_match
           - the program to produce monitor and printer tables for ralmatch
           and ralmatchx programs.

 MEASUREMENT MATERIAL
      In order to conduct measurements, the Kodak Reflection Density Guide
      (catalogue No 146 5947, Kodak Publications Q16) is needed.

 STAGE I
      Stage I of the procedure ensures that colours that are gray on the
      monitor are also gray on the printer and that the lightness of the
      screen grays linearly maps to printer lightness values. To complete
      Stage I of the procedure, execute the following steps:

      [1]  Do the monitor calibration - Run the 16shades program. It will
           display 16 gray squares with colours going from black to white in
           equidistant steps. Adjust monitor's brightness and contrast so
           that as many squares as possible appear distinct.

      [2]  Determine the monitor midtone colour - Run the midtone program.
           It will display a gray background and a rectangle with a
           chequered pattern of black and white squares in the middle of the
           screen. Adjust the colour of the background so that the
           difference in the colour between the rectangle and the background
           disappears. Type man midtone for more information on how to run
           the program. It is desirable to have more than one measurement
           result and to have up to 6 people involved, each performing this
           step separately. Results are then stored in the monitor
           measurement file (the name of the file is user defined; the
           format of the file is described later in the text).

      [3]  Determine density of the black print - Send the black.ps
           PostScript file to the printer involved in the colour matching
           exercise. A black square on the white paper will be produced.
           Measure the density of the black patch using the Kodak Reflection
           Density Guide in the following way: look through each of the
           holes from the guide and compare the colour seen through the hole
           with the colour from the Guide surrounding the hole. When the
           closest match of the two colours is achieved, read the number
           below the colour from the Guide. This is the density of the black
           square. Note: if the colour seen through the hole does not match
           any in the Guide, find two squares from the Guide, one lighter
           and the other darker than the colour from the hole and manually
           interpolate their density values. Write the results to the
           printer measurement file (the name of the file is user defined;



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 RALCOLOUR_MATCH(9)                                       RALCOLOUR_MATCH(9)
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           the format of the file is described later in the text).

      [4]  Print colour charts - Send the charts.ps PostScript file to the
           printer involved in the colour matching exercise.  A set of
           printouts will be produced, each consisting of 4, 5 X 5 squares
           filled with a solid colour. Values of the three colour
           coordinates (Cyan, Magenta and Yellow) will be printed below each
           square. Each quarter of a page should contain at least one gray-
           scale colour square. These colour charts are used in the
           subsequent printer measurement.

      [5]  Measure densities and determine the printer response
           characteristic - In order to measure densities, the Kodak Density
           Guide and colour charts are needed. The measurement procedure is
           similar to one described under paragraph 3. ( Determine density
           of the black print ). Comparing the colours from the Guide and
           colours from the charts, identify squares whose colours are
           achromatic (i.e. gray scale). Read three values (for Cyan,
           Magenta and Yellow) below these squares.  Note there should be at
           least one square per quarter page whose colour is gray scale. If
           there is not a single achromatic square on a quarter page, find a
           region on the page where a gray colour should be and manually
           interpolate Cyan, Magenta and Yellow values. The density of these
           colours should also be determined. Find the closest match of the
           colour from the charts and the colour from the Guide and then
           read the number below the colour from the Guide. Note: if the
           colour seen through the hole does not match any in the Guide,
           find two squares from the Guide, one lighter and the other darker
           than the colour from the hole and manually interpolate their
           density values.  Following this procedure a list of colour value
           triplets coupled with the density values will be produced. It is
           desirable to have more than one measurement result and to have up
           to 6 people involved, each performing this step of the whole
           procedure separately. Each person produces a separate set of
           measurement results and all results are then stored in the
           printer measurement file one after the other (the name of the
           file is user defined; the format of the file is described later
           in the text).

      [6]  Produce monitor and printer tables - run the ralcol_match program
           specifying the names of the monitor measurement and printer
           measurement result files where the results of the above
           measurements are stored. When invoking the program, names of the
           files where monitor and printer tables will be stored should be
           specified as well.

      [7]  Verification - use one of example images installed with this
           package (or an image having plenty of gray scale colours and some
           chromatic colours) and run ralmatch or ralmatchx filter program
           specifying the just created monitor and printer table files.
           Compare VDU and printer image (together with an old printer image



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 RALCOLOUR_MATCH(9)                                       RALCOLOUR_MATCH(9)
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           produced without the filter program). The colour matched print
           image should be lighter than both the VDU and the old image, but
           grays from the VDU image should be reproduced as grays on the
           colour matched print but could be chromatic on the old print. In
           the case where grays are not reproduced as grays after colour
           matching or if one is not satisfied with results in general, the
           whole procedure should be repeated.  Note the colour matched
           picture can have unsaturated colours and poorly produced black
           (i.e. the black is not black but dark gray), especially if the
           printer uses black suplement (i.e. uses black ink in addition to
           cyan, magenta and yellow ink in order to print all colour
           variations). This is because stage I of the colour matching
           procedure does not take into account black ink suplement and when
           producing printouts switches off the black colour completely.
           This problem will be cured after stage II of the colour matching
           procedure.

 STAGE II
      The stage II is part of the next release.

 STAGE III
      The stage III is part of the next release.

 FILE FORMATS
      There are two types of input files for ralcol_match : monitor
      measurements results and printer measurement results files. Their
      formats differ slightly and will be described separately.

      The two output files from the ralcol_match program are generated
      automatically and their formats will not be discussed.

 MONITOR MEASUREMENTS RESULTS FILE
      This is a simple file containing the value measured by running the
      midtone program. Each value measured by different person must be
      written as a separate line.

      example

      0.728882
      0.732697

      This is a file containing values measured by running the midtone
      program twice, each time having a different person involved in
      measurements.

 PRINTER MEASUREMENTS RESULTS FILE
      The printer measurements results file consists of several separate
      parts:

      [1]  a single line with two data values: one for the minimum density
           (measured as a density of the white paper) and second value for



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 RALCOLOUR_MATCH(9)                                       RALCOLOUR_MATCH(9)
                                 xx March 93



           the maximum density (measured as a density of a black patch
           produced by setting cyan, magenta, yellow and black colours to
           maximum).

      [2]  set of data values measured by a single person. This set consists
           of several lines, each containing four values: cyan, magenta and
           yellow colour values that produced the patch whose density was
           measured and the measured density value.

      Line containing minimum/maximum density and each set of measurements
      done by a different person are separated from each other by one or
      more line whose the first character must be # (hash). Any other
      combination of characters (or user comment) can be written after the
      first # character. It is also valid to put a heading at the beginning
      of the file, assuming that each line of the heading begins with #
      (hash) character.

      An example of the printer measurements file format is given in the
      CMYtoDensity file in the lib directory.

 LIMITATIONS
      The colour matching prodedure can be performed under following
      conditions:

      [a]  operating system - Unix;

      [b]  language - C;

      [c]  windowing system - X11 version 5 (OSF/Motif Toolkit Version 1.1
           or above
            is required in order to run the ralmatchx program, but if not
           available, the ralmatch program can be run instead);

      [d]  display - a minimum 8-bit colour;

      [e]  printer - PostScript level 1 with colour extensions;

      [f]  PostScript images - image has to be written using the RGB format
           at 8-bits per component. The image has to have lines that are at
           least 50 characters long.  Note: all the limitations imposed on
           the format of the PostScript image will be cured in future
           releases;

      [g]  Current version of the ralmatch program favours cursor movements
           using the BackSpace character. If this option is not available
           with your system, the feature can be disabled from the Makefile.

 SEE ALSO
      ralcol_match, ralmatch, ralmatchx, midtone, 16shades, charts.





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 RALCOLOUR_MATCH(9)                                       RALCOLOUR_MATCH(9)
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 AUTHORS
      R Popovic and R J May ( RAL ID ) are the original authors.




















































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