Provided by: pfstmo_2.1.0-3build4_amd64 bug

NAME

       pfstmo_fattal02 - Gradient domain high dynamic range compression

SYNOPSIS

       pfstmo_fattal02  [--alpha  <val>]  [--beta  <val>]  [--gamma  <val>]  [--saturation <val>]
       [--noise  <val>]  [--detail-level  <val>]  [--black-point  <val>]  [--white-point   <val>]
       [--multigrid] [--verbose] [--help]

DESCRIPTION

       This command implements a tone mapping operator as described in:

       Gradient  Domain High Dynamic Range Compression R. Fattal, D. Lischinski, and M. Werman In
       ACM Transactions on Graphics, 31(3), p. 249, 2002.

       With respect to the original paper,  this  program  provides  additional  parameter  which
       limits  the  amplification  of  noise.  The  noise  is  often starkly amplified because of
       division by zero in one of the equations in the paper. Extension contributed by Przemyslaw
       Bazarnik.

       At  the core of the programme is a Poisson PDE which as suggested in the original paper is
       solved using a Full Multigrid Algorithm. However, this is an iterative solver which  seems
       to  lose  accuracy  when applied to higher resolution images resulting in halo effects and
       surreal looking images. For that reason a second solver has  been  implemented  using  the
       discrete  cosine  transform  as  the  underlying  method and is considerably more accurate
       mainly because it is a direct solver. This solver is the preferred method and is  used  by
       default. The old multigrid solver can be selected with the --multigrid (-m) option.

OPTIONS

       --alpha <val>, -a <val>

              Set  alpha  parameter.  This parameter is depreciated as setting a <val> other than
              1.0 has only the effect of a global gamma adjustment of the luminance channel which
              can  be  directly  specified  using  the  --gamma  option.  See  the  paper for the
              definition of alpha. It can be shown, although not mentioned  in  the  paper,  that
              setting   alpha   other   than   1.0  has  the  same  effect  as  setting  gamma  =
              alpha^(k*(1-beta)), where beta is the value as specified by --beta  and  k  is  the
              number  of levels of the Gaussian Pyramid (see paper for details), which depends on
              the   image   pixel   size   (smallest   k   so    that    2^(k+detail_level)    >=
              min(width,height)/MSIZE, MSIZE see source code, e.g. 8 or 32).

       --beta <val>, -b <val>

              Set   beta  parameter.  <val>  sets  the  strength  of  gradient  (local  contrast)
              modification.  Suggested range is 0.8 to  0.96,  default  is  0.9  (see  paper  for
              details).  Value of 1 does not change contrasts, values above 1 reverse the effect:
              local contrast is stretched and details are attenuated.  Values below 0.5  lead  to
              very strong amplification of small contrast, so consider using --noise parameter to
              prevent noise.

       --gamma <val>, -g <val>

              Set luminance gamma  adjustment.  This  can  be  described  as  a  global  contrast
              enhancement  and  is  applied  after  the  local  enhancement  as  specified by the
              parameter --beta is performed. Gamma adjustment  or  correction  is  defined  by  a
              power-law, in this case
               L_out(x,y)  =  L_in(x,y)^gamma, where L_in(x,y)=exp(I(x,y)) is the luminance value
              after the local contrast enhancement (I is the solution of the  Poisson  PDE).  The
              suggested range for <val> is 0.6 to 1.0, default is 0.8.

       --saturation <val>, -s <val>

              Amount of color saturation. Suggested range is 0.4 to 0.8. Default value: 0.8.

       --noise <val>, -n <val>

              Reduces the gradient amplification value for gradients close to 0 and reduces noise
              as a result. <val> defines gradient value (luminance difference of adjacent pixels)
              which  is  treated  as noise. Suggested range is 0.0 to the value of alpha. Default
              value calculated based on alpha: 0.001*alpha.

       --detail-level <val>, -d <val>

              Specifies up to which  detail  level  the  local  contrast  enhancement  should  be
              performed.  It  basically  means that local contrast levels within small squares of
              pixel size 2^<val> are not changed.  In  the  implementation  this  corresponds  to
              removing the <val> finest levels of the Gaussian Pyramid as described in the paper,
              i.e. the paper only considers <val>=0. Suggested values are 1, 2 or 3; 3  for  high
              resolution  images.  The default is 3 for --fftsolver, and 0 if the original multi-
              level solver is used (to be consistent with the paper).

       --white-point <val>, -w <val>

              Specifies the percentage  of  pixels  which  are  allowed  to  be  overexposed  and
              therefore  blown  out.  This  can be useful for example when there is a very bright
              object in the image like the sun and details of it do not need to be resolved.   As
              a  result  the  overall  image will look brighter the greater <val> is.  Default is
              0.5.

       --black-point <val>, -k <val>

              Same as --white-point but for under-exposed pixels. Default is 0.1.

       --multigrid, -m

              Enable the use of the multigrid solver as suggested  by  the  original  paper.  For
              accuracy the default fft solver is generally recommended especially when using high
              resolution images. The user will benefit by obtaining photo-realistic  rather  than
              surreal  looking  images. The fft solver is also faster despite the fact it is only
              O(n*log n) with n=width*height, as compared to O(n) for the multigrid solver.   The
              speed  improvement  is  thanks to the very efficient fftw3 library which is used to
              calculate the discrete cosine transform.

       --verbose

              Print additional information during program execution.

       --help

              Print list of command line options.

EXAMPLES

       pfsin memorial.hdr | pfstmo_fattal02 -v -t | pfsout memorial.png

              Tone map image (using fft solver) and save it in png format.

       pfsin memorial.hdr | pfstmo_fattal02 -v -t -b 0.85 -g 0.7 -w 2.0 \
              | pfsout memorial.png

              Tone map image (using fft solver) with stronger contrast modification than default,
              i.e. beta=0.85, gamma=0.7 and white point 2.0%.

       pfsin memorial.hdr | pfstmo_fattal02 -v | pfsout memorial.png

              Tone map image (old style) and save it in png format.

SEE ALSO

       pfsin(1) pfsout(1) pfsview(1)

KNOWN ISSUES

       For  stronger  local  contrast  enhancements (beta<0.9) the fft solver (--fftsolver) might
       produce slightly dark image corners.  This can be mitigated using bigger  values  for  the
       --noise parameter.

       With  a  value of --detail-level greater than 0, the internal implementation could be made
       much more efficient as only a reduced sized PDE would need to be solved, greatly improving
       speed.

BUGS

       Please  report  bugs  and  comments  on  implementation  to  the pfstools discussion group
       (http://groups.google.com/group/pfstools). For bugs specific to the FFT solver email  Tino
       Kluge <tino.kluge@hrz.tu-chemnitz.de>.

                                                                               pfstmo_fattal02(1)