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)