NAME

       pfsabsolute - Convert luminance in images to absolute measure

SYNOPSIS

       pfsabsolute <dest Y> [<src Y>] [--verbose] [--help]

DESCRIPTION

       pfsabsolute  applies  all necessary operations to convert an image from relative luminance
       (tag LUMINANCE is RELATIVE) or  display-dependent  luma  (tag  LUMINANCE  is  DISPLAY)  to
       absolute  luminance  values. When the luminance in an image is absolute (tag LUMINANCE set
       to ABSOLUTE), the Y channel represents physical luminance in  cd/m^2.  Absolute  luminance
       levels  are  useful  for  some  tone  mapping  algorithms  and  also  for  image  or video
       compression.

       The argument <dest Y> denotes the level of  luminance  that  relative  luminance  <src  Y>
       should  be  rescaled to. The luminance is in fact multiplied by the ratio <dst Y>/<src Y>.
       <src Y> is normally relative luminance checked with pfsview in the spot where the absolute
       luminance  <dest  Y>  is measured, known or guessed. If <src Y> is omitted, the value 1 is
       assumed, so <dest Y> is just a scaling factor.

       In case if display-depended luma (tag LUMINANCE is DISPLAY), the inverse gamma  correction
       is  applied  (assuming  sRGB  color  space).  In such case <dest Y> is usually the maximum
       luminance of a display (e.g. 80 cd/m^2).

       This command always sets LUMINANCE tag to ABSOLUTE.

EXAMPLES

       pfsin memorial.hdr | pfsabsolute 20 0.04 | pfsview

              Multiply luminance in memorial image, so that relative luminance  0.04  becomes  20
              cd/m^2.  Normally,  the  value  0.04  is check using pfsview in the spot, where the
              absolute luminance (which equals in this case 20 cd/m^2) is known.

       pfsin lena.png | pfsabsolute 80 | pfsview

              Convert lena image  from  sRGB  color  space  to  absolute  XYZ,  assuming  maximum
              luminance of the monitor 80 cd/m^2.

SEE ALSO

       pfsgamma(1) pfsinppm(1)

BUGS

       Please report bugs and comments to Rafal Mantiuk <mantiuk@mpi-sb.mpg.de>.

                                                                                   pfsabsolute(1)