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ccdspec - print spectrum at a grid point in an image cube
ccdspec
[parameter=value]
ccdspec prints the spectrum (see also snapprint(1NEMO)
for more flexible options) to stdout, with a commented line that adds some
statistics on the standard deviation of the series and that of the differentials.
It also computes sigma_diff/sigma/sqrt(2)
, which should be 1 if the spectrum
is normal and uncorrelated noise. In general smoothing and/or a signal
will lower this value.
The following parameters are recognized
in any order if the keyword is also given:
- in=
- Input filename. No default.
- x=
- Pixel in X to print (0=1st pixel). By default it uses the center of the
map.
- y=
- Pixel in Y to print.
- z=
- Pixel range in Z to select. By default all
pixels are selected.
- scale=fac1,fac2
- Output scaling factors for the spectral
axis (fac1) and cube value (fac2). Note the mean/sigma output will also
be scaled by fac2. [Default: 1,1]
Here is an example creating a
spectrum with uncorrelated noise. The stats mentioned in the commented last
line ar the pixel position and length of spectral axis, and mean/sigma
for the signal, and mean/sigma he differential spectrum. The last number
is the ratio of the two sigma and sqrt(2)
, which for normal gaussian noise
should be 1.
% ccdgen "" - noise 0,1 size=1,1,8000 seed=123 | ccdspec - | tail -3
7998 -1.06975
7999 0.944338
# 0 0 8000 mean/sig 0.00102038 1.00182 9.94952e-05 1.41469 0.998513
although tabhist(1NEMO)
with median=f gives the same stats
% ccdgen "" - noise 0,1 size=1,1,8000 seed=123 | ccdspec - | tabhist - 2 median=f
Mean and dispersion : 0.00102037 1.00182 0.0112014
Diff mean and disp : 9.94952e-05 1.41469 0.998513
and if an extra hanning smoothing is done, the correlation is less than
one (sqrt(1/3)):
% ccdgen "" - noise 0,1 size=1,1,8000 seed=123 | ccdsmooth - - dir=z | ccdspec
- | tail -3
7998 -0.151399
7999 0.204732
# 0 0 8000 mean/sig 0.000986234 0.616406 4.92386e-05 0.49548 0.568387
ccdgen(1NEMO)
, ccdprint(1NEMO)
, tabhist(1NEMO)
, tabtrend(1NEMO)
src/image/io
Peter Teuben
11-Feb-2021 V0.3 Created Q&D PJT
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