Description

immoments task: Compute moments from an image

The spectral moment distributions at each pixel are determined. The main control of the calculation is given by the parameter moments:

  • moments = -1 - mean value of the spectrum
  • moments =  0 - integrated value of the spectrum
  • moments =  1 - intensity weighted coordinate; traditionally used to get "velocity fields"
  • moments =  2 - intensity weighted dispersion of the coordinate; traditionally used to get "velocity dispersion"
  • moments =  3 - median value of the spectrum
  • moments =  4 - median coordinate
  • moments =  5 - standard deviation about the mean of the spectrum
  • moments =  6 - root mean square of the spectrum
  • moments =  7 - absolute mean deviation of the spectrum
  • moments =  8 - maximum value of the spectrum
  • moments =  9 - coordinate of the maximum value of the spectrum
  • moments = 10 - minimum value of the spectrum
  • moments = 11 - coordinate of the minimum value of the spectrum

The default value of outfile is the input image name appended by an auto-determined suffix.

If stretch=True and if the number of mask dimensions is less than or equal to the number of image dimensions and some axes in the mask are degenerate while the corresponding axes in the image are not, the mask will be stetched in the degenerate axis dimensions. For example, if the input image has shape [100, 200, 10] and the input mask has shape [100, 200, 1] and stretch=True, the mask will be stretched along the third dimension to shape [100, 200, 10]. However if the mask is shape [100, 200, 2], stretching is not possible and an error will result.

If an image has multiple per-channel beams and the moment axis is equal to the spectral axis, each channel will be convolved with a beam that has a minimum area necessary to contain each of the image beams, ie, it is the minimum area common beam to which all the beams in the image can be convolved.

 

Task-specific parameter summary

moments

List of moments to compute. See above for details.

axis

Axis along which to compute the specified moments.

includepix

Range of pixel values to include in the computation. A range can only be given for one of includepix or excludepix.

excludepix

Range of pixel values to exclude in the computation. A range can only be given for one of includepix or excludepix.