Introduction to Library Functions       XSolarisGetVisualGamma(3)

NAME
     XSolarisGetVisualGamma -  obtain  gamma  information  for  a
     visual

SYNTAX
     #include <X11/Xmu/XmuSolaris.h>

     Status
     XSolarisGetVisualGamma(Display *display, int screen_number,
                      Visual *visual, double *gamma)

ARGUMENTS
     display   Specifies the connection to the X server.

     screen_number
               Specifies the number of the screen.

     visual    Specifies the visual.

     gamma     Returns the gamma value for the specified visual.

DESCRIPTION
     The XSolarisGetVisualGamma function returns the gamma  value
     of  a  specified  visual.  This value is the exponent of the
     power function describing the intensity response  of  colors
     displayed using that visual.  This is the intensity response
     of the entire path from the frame buffer pixel store through
     the monitor.  The equation of the intensity response is:

          IntensityOut = (FramebufferColor)**gamma

     (i.e. the color in the frame buffer raised to the  power  of
     gamma).

     FramebufferColor refers to the the RGB values stored in  the
     frame  buffer pixel store and processed by any color mapping
     LUTs that are in the output path.

     Gamma correction is  necessary  because  of  the  way  color
     intensities  are perceived by the human eye.   Without gamma
     correction, the eye interprets changes to the  color  inten-
     sity  incorrectly.   Small  changes  to  low intensity light
     appear to have more effect than  the  equivalent  change  to
     higher  intensity  light.   This  distorts the appearance of
     graphical entities which depend on accurate color,  such  as
     images, anti-aliased lines and transparent polygons.

     Gamma correction results in a linear mapping  between  color
     values and percieved intensity.  Gamma corrected visuals are
     also called linear visuals for this reason.  Linear  visuals
     have a gamma value of 1.0.

SunOS 5.8          Last change: 11 March 1994                   1

Introduction to Library Functions       XSolarisGetVisualGamma(3)

     Note: the term "gamma" used here refers the mapping  applied
     along  the  entire  path(that is, the value percieved by the
     end user), not merely the exponent of the  gamma  correction
     function.

     The gamma value returned defines the color-to-intensity map-
     ping for all three channels: red, green, and blue.

     A status of Success is returned if the function was able  to
     determine  the  gamma  successfully.   If  a request failure
     occured while calling the function, a BadAccess  error  code
     is  returned.   If  there is an internal inconsistency (e.g.
     the gamma value for one of the color channels  is  different
     from  the  others) a BadMatch error code is returned.  When-
     ever an error code is returned, the argument gamma  is  left
     untouched.

     The gamma value returned  represents  the  best  information
     available  on the intensity response of the visual.  Depend-
     ing on the device, it may or may not include the actual mon-
     itor  characteristics (some devices have no way of determin-
     ing the type of monitor so they may assume a default monitor
     gamma).   As  such,  it represents the system's "best guess"
     about the intensity response.  Since this function gets  its
     information  from  the  same  property used by Solaris color
     managment systems, if more accurate information on the moni-
     tor  response is configured or calibrated through these sys-
     tems, this function will return a more  accurate  value  for
     gamma.

     If the intensity  mapping  is  not  a  power  function,  the
     returned  gamma  value may only be approximate.  This should
     usually happen only when the  device  gamma  correction  has
     been incorrectly configured.

     To use  this  function,  an  application  should  link  with
     libXmu.

SEE ALSO
     Solaris X Window System Developer's Guide
     (Visuals and Display Devices chapter)

SunOS 5.8          Last change: 11 March 1994                   2