1pfsabsolute(1)              General Commands Manual             pfsabsolute(1)
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NAME

6       pfsabsolute - Convert luminance in images to absolute measure
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SYNOPSIS

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

12       pfsabsolute  applies  all necessary operations to convert an image from
13       relative luminance (tag LUMINANCE  is  RELATIVE)  or  display-dependent
14       luma  (tag LUMINANCE is DISPLAY) to absolute luminance values. When the
15       luminance in an image is absolute (tag LUMINANCE set to ABSOLUTE),  the
16       Y  channel  represents physical luminance in cd/m^2. Absolute luminance
17       levels are useful for some tone mapping algorithms and also  for  image
18       or video compression.
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20       The  argument  <dest  Y>  denotes  the level of luminance that relative
21       luminance <src Y> should be rescaled to. The luminance is in fact  mul‐
22       tiplied  by  the  ratio  <dst  Y>/<src Y>. <src Y> is normally relative
23       luminance checked with pfsview in the spot where the absolute luminance
24       <dest  Y>  is  measured,  known  or guessed. If <src Y> is omitted, the
25       value 1 is assumed, so <dest Y> is just a scaling factor.
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27       In case if  display-depended  luma  (tag  LUMINANCE  is  DISPLAY),  the
28       inverse  gamma  correction  is  applied (assuming sRGB color space). In
29       such case <dest Y> is usually the maximum luminance of a display  (e.g.
30       80 cd/m^2).
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32       This command always sets LUMINANCE tag to ABSOLUTE.
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EXAMPLES

36       pfsin memorial.hdr | pfsabsolute 20 0.04 | pfsview
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38              Multiply luminance in memorial image, so that relative luminance
39              0.04 becomes 20 cd/m^2. Normally, the value 0.04 is check  using
40              pfsview  in the spot, where the absolute luminance (which equals
41              in this case 20 cd/m^2) is known.
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44       pfsin lena.png | pfsabsolute 80 | pfsview
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46              Convert lena image from sRGB color space to absolute XYZ, assum‐
47              ing maximum luminance of the monitor 80 cd/m^2.
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SEE ALSO

51       pfsgamma(1) pfsinppm(1)
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BUGS

54       Please   report  bugs  and  comments  to  Rafal  Mantiuk  <mantiuk@mpi-
55       sb.mpg.de>.
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59                                                                pfsabsolute(1)