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imom - Compute intensity-weighted moment of an image  




image analysis  


IMOM finds the 'centroid' of a Miriad image, and the 'spread' about that centroid, by evaluating the expressions
    mom1 = SUM{ I(x)*x } / SUM{ I(x) }
    mom2 = sqrt( SUM{ I(x)*(x-mom1)**2 } / SUM{ I(x) } )
along the first two axes of an image.

Notes: * The first moment should always be in the range 1..naxis(n). * mom2 is equivalent to the standard deviation, not the FWHM,

  for a gaussian intensity distribution.
* mom2 shows the spread along the directions parallel to the
  *image axes*. So if your object of interest is elongated along 
  some random angle, the mom2 values returned will be a combination
  of the major and minor-axis sizes, projected onto the x- and y-axes.
* If all pixels in the region are blank, moments of -1.0 are returned
  and a warning is printed.
* In case of a rounding error etc, moments of 0.0 are returned
  and a warning is printed.


Input image name. No default.
The following options can be given (minimum match applies):
    Compute the 'third moment'. Since the formal third moment
    has the rather useless dimensions of pixel**3, what
    is actually returned is the dimensionless quantity
         SUM{ I(x)*(x - mom1)**3 } / SUM{ I(x) } / mom2**3.
    A negative value means the distribution is skewed towards
    values less than the first moment; i.e. the pixels at
    lower pixel number than mom1 are generally brighter than
    those at higher pixel number. A positive value
    means the pixels at higher pixel number than the first
    moment are brighter.
    When you use this program to estimate the peak of a source,
    better accuracy can be had by ignoring low-intensity values.
    Setting this option forms the moments using only pixels that
    are brighter than the (local) mean.
    If a min or max value is specified (see below), the mean is
    computed using only the values within the selected range.
    Forms moments using just the pixels brighter than
    local_mean + local_rms.
    If a min or max value is specified, the mean and rms are computed
    using only the values within the selected range.
The region of interest. See the help on "region" for more information. This gives the region of pixels to calculate the moments within. Only rectangular regions are supported. The default is the entire image. If a cube is given as the input image, the program computes moments for each plane along axis 3 (within the selected range).
The minimum pixel value for inclusion in the moment calculation. The default is the image minimum.
The maximum pixel value for inclusion in the moment calculation The default is the image maximum.
The output log file. The default is the terminal. Output to the terminal is paged.




This document was created by man2html, using the manual pages.
Time: 18:35:38 GMT, July 05, 2011