pfstmo_fattal02(1)pfstmo_fattal02(1)NAMEpfstmo_fattal02 - Gradient domain high dynamic range compression
SYNOPSISpfstmo_fattal02 [--alpha <val>] [--beta <val>] [--gamma <val>] [--satu‐
ration <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. Lischin‐
ski, 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 look‐
ing images. For that reason a second solver has been implemented using
the discrete cosine transform as the underlying method and is consider‐
ably 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 speci‐
fied 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 con‐
trasts, 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 enhance‐
ment 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 over‐
exposed 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 over‐
all 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 orig‐
inal 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 sur‐
real 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 modifi‐
cation 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 ALSOpfsin(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 implementa‐
tion 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 dis‐
cussion group (http://groups.google.com/group/pfstools). For bugs spe‐
cific to the FFT solver email Tino Kluge <tino.kluge@hrz.tu-chem‐
nitz.de>.
pfstmo_fattal02(1)
