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Basic Information on imom

Task: imom
Purpose: Compute intensity-weighted moment of an image
Categories: 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.
        * 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.

Key: in
        Input image name. No default.

Key: options
        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.

Key: region
        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).

Key: min
        The minimum pixel value for inclusion in the moment calculation.
        The default is the image minimum.

Key: max
        The maximum pixel value for inclusion in the moment calculation
        The default is the image maximum.

Key: log
        The output log file. The default is the terminal. Output to
        the terminal is paged.
Revision: 1.6, 2012/02/29 23:54:44 UTC

Generated by miriad@atnf.csiro.au on 21 Jun 2016