From 40e5a5811c6ffce9b0974e93cdd927cbcf60c157 Mon Sep 17 00:00:00 2001 From: Joe Hunkeler Date: Tue, 11 Aug 2015 16:51:37 -0400 Subject: Repatch (from linux) of OSX IRAF --- pkg/proto/doc/mimstat.hlp | 179 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 179 insertions(+) create mode 100644 pkg/proto/doc/mimstat.hlp (limited to 'pkg/proto/doc/mimstat.hlp') diff --git a/pkg/proto/doc/mimstat.hlp b/pkg/proto/doc/mimstat.hlp new file mode 100644 index 00000000..c6c389ea --- /dev/null +++ b/pkg/proto/doc/mimstat.hlp @@ -0,0 +1,179 @@ +.help mimstatistics Sep01 proto +.ih +NAME +mimstatistics -- compute and print image pixel statistics using iterative +rejection and masks +.ih +USAGE +imstatistics images +.ih +PARAMETERS +.ls images +The input images or image sections for which pixel statistics are to be +computed. Image sections are automatically applied to the input masks +\fIimasks\fR if input masks are not mask sections. +.le +.ls imasks = "" +The list of input masks or input mask sections associated with \fIimages\fR. +Good and bad data values are assumed to be presented by mask values of 0 and +1 respectively. The number of input masks must be 0, 1, or equal to the number +of input images. Input mask sections if present override the input image +sections. +.le +.ls omasks = "" +The list of output masks which are a combination of the input mask if any +and pixels rejected using the good data limits and / or iterative clipping. +Data used to compute the statistics are represented by 0 in the output mask, +rejected data by zero. The number of output masks must be 0 or equal to +the number of input images. +.le +.ls fields = "image,npix,mean,stddev,min,max" +The statistical quantities to be computed and printed. +.le +.ls lower = INDEF +The minimum good data limit. All pixels are above the default value of INDEF. +.le +.ls upper = INDEF +The maximum good data limit. All pixels are above the default value of INDEF. +.le +.ls nclip = 0 +The maximum number of iterative clipping cycles. By default no clipping is +performed. +.le +.ls lsigma = 3.0 +The low side clipping factor in sigma. +.le +.ls usigma = 3.0 +The high side clipping factor in sigma. +.le +.ls binwidth = 0.1 +The width of the histogram bins in sigma used for computing the midpoint +(estimate of the median) and the mode. +.le +.ls format = yes +Label the output columns and print the results in fixed format ? If format +is "no" no column labels are printed and the output is in free format. +.le +.ls cache = no +Cache the image data in memory ? This can increase the efficiency of the +task if nclip > 0 or if either of the midpt or mode statistics is computed. +.le +.ih +DESCRIPTION +The statistical quantities specified by the parameter \fIfields\fR are +computed and printed for each image in the list specified by \fIimages\fR. +The results are printed in tabular form with the fields listed in the order +they are specified in the fields parameter. The available fields are the +following: + +.nf + image - the image name + mask - the mask name + npix - the number of pixels used to do the statistics + mean - the mean of the pixel distribution + midpt - estimate of the median of the pixel distribution + mode - the mode of the pixel distribution + stddev - the standard deviation of the pixel distribution + skew - the skew of the pixel distribution + kurtosis - the kurtosis of the pixel distribution + min - the minimum pixel value + max - the maximum pixel value +.fi + +The mean, standard deviation, skew, kurtosis, min and max are computed in a +single pass through the image using the expressions listed below. +Only the quantities selected by the fields parameter are actually computed. + +.nf + mean = sum (x1,...,xN) / N + y = x - mean + variance = sum (y1 ** 2,...,yN ** 2) / (N-1) + stddev = sqrt (variance) + skew = sum ((y1 / stddev) ** 3,...,(yN / stddev) ** 3) / (N-1) + kurtosis = sum ((y1 / stddev) ** 4,...,(yN / stddev) ** 4) / (N-1) - 3 +.fi + +The midpoint and mode are computed in two passes through the image. In the +first pass the standard deviation of the pixels is calculated and used +with the \fIbinwidth\fR parameter to compute the resolution of the data +histogram. The midpoint is estimated by integrating the histogram and +computing by interpolation the data value at which exactly half the +pixels are below that data value and half are above it. The mode is +computed by locating the maximum of the data histogram and fitting the +peak by parabolic interpolation. + +Pixels are rejected from the initial statistics computation by specifying an +input mask \fIimasks\fR or by setting the good data limits \fIlower\fR +and \fIupper\fR. Iterative rejection can be performed by setting the +clipping parameters \fInclip\fR, \fIlsigma\fR, and \fIusigma\fR. + +The input masks \fIimasks\fR can be specified in a variety of ways as +shown below. + +.nf + "" - empty mask, use all the pixels + EMPTY - empty mask, use all the pixels + !KEYWORD - use mask specified by header keyword KEYWORD + !^KEYWORD - use inverse of mask specified by header keyword KEYWORD + mask - use specified mask + ^mask - use inverse of specified mask +.fi + +In all cases the mask values are assumed to be 0 in good data regions and +non-zero in rejected data regions. The input masks may in pixel list, e.g. +".pl" format, or integer images format, e.g. ".imh", ".fits", etc. + + +.ih +EXAMPLES +1. Find the number of pixels, mean, standard deviation and the minimum +and maximum pixel value of a bias region in an image. + +.nf + cl> mimstat flat*[*,1] "" + # IMAGE NPIX MEAN STDDEV MIN MAX + flat1[*,1] 800 999.5 14.09 941. 1062. + flat2[*,1] 800 999.4 28.87 918. 1413. +.fi + +The string "flat*" uses a wildcard to select all images beginning with the +word flat. The string "[*,1]" is an image section selecting row 1. + +2. Compute the mean, midpoint, mode and standard deviation of a pixel +distribution. + +.nf + cl> mimstat m51 "" fields="image,mean,midpt,mode,stddev" + # IMAGE PIXELS MEAN MIDPT MODE STDDEV + M51 262144 108.3 88.75 49.4 131.3 +.fi + +3. Compute the image statistics in an image section using a mask. + +.nf + cl> mimstat m51[200:400,200:400] imasks=M51.bpm.pl + + cl> mimstat m51[200:400,200:400] imasks=M51.bpm.pl[200:400,200:400] + + cl> mimstat m51[200:400,200:400] imasks=M51.crm.pl[1:201,1:201] +.fi + +Note that the first two examples are equivalent so there is no need to +specify the input mask section in the second case. + +4. Compute the image statistics using interactive rejection and save the +rejected pixel mask. + +.nf + cl> mimstat m51 omasks=m51.rej.pl nclip=3 +.fi + +.ih +BUGS +When using a very large number of pixels the accumulation of the sums +of the pixel values to the various powers may encounter roundoff error. +This is significant when the true standard deviation is small compared +to the mean. +.ih +SEE ALSO +.endhelp -- cgit