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ccdsmooth - smoothing of an image map (2D or 3D)


ccdsmooth in=image out=image [parameter=value]


ccdsmooth will smooth an image cube through a simple direct convolution (no FFT). The smoothing beam must be circular/spherical, or smoothing must be done independantly per coordinate by calling ccdsmooth multiple times using the dir= keyword (see below).

For more artistic versions of a smoothing operation, such as added noise and diffraction spikes for bright stars, see ccddiffract(1NEMO) .


The following parameters are recognized in any order if the keyword is also given:
input file, in Image(5) format [no default]
output file, will be in Image(5) format [no default]
Beam size (FWHM, note FWHM = 2*sqrt(2*ln(2) ) = 2.355 * sigma) of a gaussian smoothing kernel. Note this is size of the used smoothing kernel, NOT the resulting beam in the output map. If this parameter is used, the parameter smooth is ignored [default: not used].
Direction of smoothing. This gives the flexibility of smoothing in x, y and/or z separately. Note that when smoothing in more than one coordinate the beam is forced to be the same in each dimension [default: xy].
Smoothing array, should be at least 1 number, prefarably normalized to unity for sake for conservation of units (mass per unit square length). The program does not normalize the beam to unity. Example is e.g. the Hanning smoothing: "0.25,0.5,0.25". [default: 0.25,0.5,0.25]. This parameter is only used if gauss parameter is not used.
Number of times the above smoothing kernel is applied over the data. [default: 1].
Input pixel value which to skip in smoothing. [Default: not used]
Value at which to cutoff the gaussian beam. [Default: 0.01]

See Also

ccdfill(1NEMO) , ccddiffract(1NEMO) , snapccd(1NEMO) , snapsmooth(1NEMO) , snapgrid(1NEMO) , image(5NEMO)


With 68881 on SUN 3/50 (~16Mhz) and 200*200 map - old program (pre-V2.1)
Nbeam=17    54s
Nbeam=33    98s
Nbeam=47    140s
HanningThe following are the weights needed in smooth= for subsequent hanning
1: 0.25,0.5,0.25
2: 0.0625,0.25,0.375,0.25,0.0625 
3: 0.015625,0.09375,0.234375,0.3125,0.234375,0.09375,0.015625 
4: 0.00390625,0.03125,0.109375,0.21875,0.273438,0.21875,0.109375,0.03125,0.00390625

and these results in a reduction of the RMS by 0.61, 0.52, 0.47 and 0.44 resp. Note this is not the official Hanning definition (0.5-0.5 cos(2.pi.N/(M-1))).
1: 0.25,0.5,0.25
2: 0.08333333,0.25,0.33333333,0.25,0.08333333
3: 0.03661165,0.125,0.21338835,0.25,0.21338835,0.125,0.03661165,
4: 0.0190983,0.0690983,0.1309017,0.1809017,0.2,0.1809017,0.1309017,0.0690983,0.0190983
5: 0.01116455,0.04166667,0.08333333,0.125,0.15550212,0.16666667,0.15550212,0.125,0.08333333,0.04166667,0.01116455
which reduce the RMS by 0.61, 0.49, 0.43, 0.38 and 0.34 resp.


Smoothing a map which has already been smoothed will result in an incorrect header - this would be a simple sum of squares, if the beams are aligned with the axis.


Peter Teuben


src/image/trans         ccdsmooth.c

Update History

29-jun-87    V1.0: Created as module from CCD program    PJT
30-Jun-87    V1.1: improved ’struct’ filestructure          PJT
 9-jul-87    V1.2: keyword ’dir’ and keyword order changed    PJT
 1-jun-88    V2.0: new filestruct, although code is same    PJT
 5-feb-89    V2.2: general 3D smoothing                    PJT
11-sep-91    some additional comments                    PJT
12-mar-98    V3.1: added cut=, fixed fwhm=0.0             PJT

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