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Name

ccdhist - histogram plotter and gaussian fit for image data

Synopsis

ccdhist in=infile [parameter=value]

Description

ccdhist plots a histogram and computes the first 4 moments of points obtained from the data values of an image(5NEMO) cube. It calculates the mean, dispersion, skewness and kurtosis. It then plots the data in the form of a histogram, optionally with a ’best’ gaussian fit and residuals. It can also plot a cumulative histogram of the data.

The median is also optionally computed, for which an alternate sorting routine can be selected (if available).

Using the nsigma keyword, outliers can be removed and statistics re-computed (a.k.a. sigma-clipping).

This program was derived from tabhist(1NEMO) , which works on ASCII tables, and derived much of it’s user interface from that program.

Parameters

The following parameters are recognized in any order if the keyword is also given:
in=infile
input file, in tabular format [no default].
xmin=x_min
Minimum value along X-axis to include [default: autoscaling on minimum of datapoints].
xmax=x_max
Maximum value along X-axis to include [default: autoscaling on maximum of datapoints].
bins=n_bins
If one number is given, it is the number of (equal size) bins between min and max. If more than one number is given, they are the bin edges (thus one more than the number of bins need to be supplied). [default: 16].
maxcount=count
Maximum count value per bin plotted along the Y-axis [default: autoscaling].
ylog=t|f
Take log of Y-axis? This option is really redundant, since tabmath(1NEMO) can handle any transformation [default: f].
xlab=x-label
Label along the X-axis [default: value].
ylab=y-label
Label along the Y-axis [default: N or log(N)].
headline=text
Random verbiage, will be plotted along right top of plot for identification [default: none]. The left top will contain the filename infile.
tab=t|f
Table output? If false, a plot using your current yapp(5NEMO) device will be given. If true, a simple ascii version of a histogram is shown. The default choice of bins=16 keeps all the information on a simple 80*24 screen. [Default: f]
gauss=t|f
If true, plot output will contain a gaussian fit. The "best" gaussian fit is the one that has the same mean, dispersion and integrated area as the data. [Default: t].
residual=t|f
If true, the residual (data - fit) will be plotted as a dashed line. [Default: t].
cumul=t|f
Plot a cumulative histogram instead. If set, the keywords gauss, residual, and ylog are automatically re-set to false. [Default: f].
integrate=t|f
Integrate the cumulative histogram, instead of number count. This option makes no sense when cumulative is not selected. [Default: f].
median=t|f
Compute median too? This can be timeconsuming for large numbers of points. [Default: t].
median=
If used, use this as blankval. Default: none.
dual=t|f
Dual pass over the data, subtracting the mean. This can be important if the data have a large average value with a small spread around the mean. Notice that in this mode the mean is subtracted but never added to the min/max/mean/median etc. Default: f
nsigma=
Delete points more than nsigma times the sigma from the mean. Also known as sigma-clipping. After each point sigma and mean are recomputed. [Default: none]
sort=sort_mode

Bugs

Points that fall exactly on the boundary of a bin, are added to the right side. Another way of saying is that a cell includes the left side, but is open ended on the right side, i.e. [---). Note this behavior is exactly opposite that of SM’s behavior, which was used to compare results.

See Also

tabhist(1NEMO) , ccdstat(1NEMO)

Author

Peter Teuben

Files


~/src/image/misc    sources

Update History


8-feb-2011    V1.0: cloned off tabhist    PJT


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