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Basic Information on imhist
Task: imhist
Purpose: Plot a histogram of the data
Categories: map analysis
Imhist makes histograms of image data. The output can be written to
the terminal, a log file, or a plot.
A gaussian curve with the same mean, rms and integral is drawn in
the histogram (this can be turned off using the 'nogauss' option).
The plotheader can be suppressed by using options=noheader. An
alternative title can be put on the plot by options=title. A useful
combination is 'options=noh,t,title', to get only the string 'title',
instead of the full header.
Key: in
This is the standard name for an input dataset -- usually
an image, though sometimes either an image or visibility dataset
or some foreign dataset format. Some tasks support multiple
input datasets at a time (with wildcard supported) whereas
others can handle only a single one at a time. There is
generally no default input name.
Key: region
the userguide.
This selects a subregion of an image. Multiple subregions can be
selected, which are "ored" together. The following subcommands are
recognized (each of which can be abbreviated to uniqueness).
images(z1,z2)
Select image planes z1 to z2 inclusive. z2 defaults to z1.
quarter(z1,z2)
Select the inner quarter of the image planes z1 to z2 inclusive.
If both z1 and z2 are missing, then all planes are selected. If
only z2 is omitted, z2 defaults to z1.
boxes(xmin,ymin,xmax,ymax)(z1,z2)
Select the pixels within a box with corners xmin,ymin,xmax,ymax.
z1 and z2 are the same as in the "image" subcommand. If z1 and z2
are omitted, all planes are selected.
polygon(x0,y0,x1,y1,x2,y2,...)(z1,z2)
Select the pixels within the polygon defined by the list of vertices.
z1 and z2 are the same as in the "image" subcommand. If z1 and z2 are
missing, all planes are selected. If only z2 is omitted, it defaults
to z1.
mask(file)
Select pixels according to the mask given in the file.
The units of the numbers given in the above commands are, in
general, absolute pixels. But this can be changed (and rechanged)
by using one of the following subcommands.
abspixel
Coordinates are interpreted as absolute pixel values, the default.
relpixel
Coordinates are relative to the reference pixel of the map.
relcenter
Coordinates are relative to the central pixel of the map,
(defined as (naxis1/2+1,naxis2/2+1)).
arcsec
Coordinates are in arcseconds, relative to the reference pixel.
kms
Coordinates in the third dimension are in km/s.
For the moment imhist only recognizes rectangular boxes.
Key: options
These options allow to control the plot. They may be abbreviated to
uniqueness. Several options may be combined, in random order.
Possible options are (# means: give a number):
'nbin,#' Select the number of bins of the histogram, default 25
'binsize,#' Select a fixed size for the bins
'cumulative' Make the histogram cumulative
'logarithmic' Make the y-scale of the histogram logarithmic
'nogauss' Do not plot the smooth gaussian curve
'cutoutliers,#' Loop through dataset twice, first to determine rms.
On second loop, set cut to average plus/minus this
value times the rms
'noheader' Do not write the header information, just the numbers,
producing an ASCII file for a plotting program
'nolist' Do not write the statistics to the screen/logfile
'xmin,#' Left edge of histogram plot, default determined from
selected data
'xmax,#' Right edge of histogram plot, default determined from
selected data
'ymax,#' The plot will be cut off at this y-value, default
is 1.25 times maximum histogram value
'title,#1,#2,#3' Put the string #1 at x-position #2 and y-position #3,
with positions measured in units of the coordinates
on the axes. If 'title' is the last option, the title
is put in the upper left hand corner.
'style,#' This selects the plot style.
#=connect means connect the datapoints
#=step means make one-bin wide connected horizontal
line segments
#=histo means bins are drawn as a horizontal line
surrounded by two vertical lines
Key: cutoff
All datavalues below the cutoff are not used for the calculation of
the histogram.
If two values, all datavalues above second value are also not used.
If second or third values is the string ',abs', a cutoff in the
absolute value of the datavalues is used.
Default is no cutoff.
Key: device
This keyword is used to specify the plotting device. It uses
the normal PGPLOT format of
file/type
or
device/type
Usually there exists a default file name or device name.
The part after the slash gives the plotter type. Examples of the
type are:
xs X-windows output. This window is resizeable and
persistent. Prepending a number allows you to use multiple
windows, e.g. 1/xs, 2/xs etc.
xd X-windows output. A transient window that disappears
when your task exists.
ps Postscript (landscape mode).
vps Postscript (portrait mode).
cps Color postscript (landscape mode).
gif gif files. Only supported with g77, not gfortran.
vcps Color postscript (portrait mode).
tek Tektronix 4010 or equivalent.
xterm Xterm window (better for simple plots over slow X links).
A `?' as device name generates a complete list of the recognized
types (which will most likely vary from system to system).
Files created for hardcopy devices must be spooled to the printer
separately. The command needed for this is site and device specific.
Key: log
If specified, output is written to the file given by log= instead
of to the terminal.