          ͻ
                                                                   
                        Color Vision Demonstrations                
                                                                   
                                 Hans Irtel                        
                           University Regensburg                   
                                    1991                           
                                                                   
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                         Installation Level 1                               
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Running CVD requires:

                o An IBM PC or compatible
		o MS-DOS 3.2 or later
		o Mouse with driver installed
		o VGA color graphics adapter
		o VGA analog color monitor

No special setup is necessary for this level of installation.


Command line to run the program:

     CVD [options]

These options are available:

     -b                   Show a monitor test image for adjusting the 
                          brightness and contrast settings.

     -d                   Use German Text

     -e                   Use English Text (default)

     -q                   Suppress the color selection field.
       
     -g <gammatable>      This option enables CVD to use a special gamma table
                          file. The format of these files is described in
                          the PXL Reference Manual (H. Irtel (1991): PXL:  A
                          Library for Programming Psychological Experiments. 
                          Unpublished manuscript.). The default is to use an
                          approximate gamma table with L=E^(2.5).


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                          Setting up the Monitor                            
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The color demonstrations of CVD require rather careful monitor settings and
surround conditions.


I. Surround Conditions

Optimal surround conditions for color demonstrations require photopic
adaptation conditions and no light from other sources directly falling on
the screen. Thus illuminate the room but position the light source behind
the monitor.


II. Monitor Adjustments

Each monitor allows controlling its luminance response by a brightness and a
contrast setting. Adjusting these is a two step procedure:

1. Areas with zero intensity have to be completely black. There must be no
   visible background signal. Set the brightness control to zero and increase
   it until there is some visible background intensity. Now reduce it again
   until the background stimulus is gone. This puts the monitor's zero point
   as high as possible without creating desaturation by a background signal.

2. White areas of maximum intensity must be as bright as possible without
   having color fringes or loosing clarity. Increase the contrast control as
   far as possible without getting images with color fringes.

To help in monitor adjustment the program CVD may be started with the option
-b in the command line. In this case a dark and a bright rectangle are
shown. Use the dark rectangle for step 1 and the bright rectangle for step
2. Both rectangles contain three vertical stripes. The inner stripe is
slightly brighter than the outer ones. The differences should be visible
both in the dark and in the bright area. So adjust the monitor such that

        a) the dark area is hardly noticable different from the background
	   and the inner stripe is slightly brighter than the outer stripes,
	   and 

        b) the bright field is as bright as possible but the inner and outer
           stripes still are discriminable.

Use the brightness control for a) and the contrast control for b).


III. Geometry

To get the correct geometry the monitor's horizontal and vertical size has
to be adjusted such that the single fields of the chromaticity diagram are
right squares.


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                           Installation Level 2                             
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The program CVD is based on PXL, the author's library for programming
psychological experiments. This library provides a second level of
installation and system tuning for any program that is written with it.  The
previously described first level is sufficient for using CVD in classroom
demonstrations. Using CVD as a research tool may require a more precise
calibration.

This is available via a special startup file and a set of parameters which
control PXL's inner working. The startup file is called STARTUP.PXL and may
reside in the current directory or in a directory which is indicated by an
environment variable. This variable's name is PXLTABLES.  It has to contain
the full path name of the directory where the startup file may be found.
Environment variables are set on the DOS command line by the SET command. An
example is 

        SET PXLTABLES=C:\CVD

which sets the file path to the directory CVD on drive C. 

Here is an example of a startup file which sets physical screen size, the
red, green, and blue screen phosphor chromaticities and the maximum
luminance values for the three color channels:

startup
	screenwidth = 2260
	screenheight = 1820
	redprimaryx = 0.640
	redprimaryy = 0.330
	redprimaryL = 28.9
	greenprimaryx = 0.290
	greenprimaryy = 0.600
	greenprimaryL = 103.4
	blueprimaryx = 0.150
	blueprimaryy = 0.060
	blueprimaryL = 11.61
end

Note that there are certain syntactical restrictions within the startup file.
It has to begin with the keyword "startup" and end with "end". Parameters
are named, the meaning of the names in the example is apparent. screen width
and height are specified in 1 thenth of a millimeter. The luminance values
of the primaries specify the maximum luminance in candela per square meter
for the respective channel. Phosphor chromaticities are given in CIE 1931
xy-chromaticity coordinates. 

The most precise level of calibration available is a gamma table with actual
measurements of the luminance response functions.  Please contact the author
if you need more information on calibration. 



Author: Hans Irtel
	Universitt Regensburg
	Institut fr Psychologie
	Universittsstr. 31
	8400 Regensburg

E-Mail: irtel@vax1.rz.uni-regensburg.dbp.de


