Track Centroids in Array of Windows

This option is designed to find the intensity centroid for an array of windows in a range of buffers and to write the data out to a file. This facility may be used for determining the motion of an array of entities provided they remain within the original window specified.

Find centroid in which buffer ?

This entry specifies one of the buffers in which the window centroids are to be located. Any valid DigImage buffer may be specified. The buffer will be displayed while the centroids are being located.

Another buffer ? A positive answer (<Y> or <return>) will allow a further buffer to be specified for searching. No (<N> or <space>) indicates that all the buffers have been specified.

Window Specification: Region to centroid

The windows submenu is produced to allow interactive specification of the region(s) for which the intensity centroid is to be found. One window may be specified each time the submenu is entered. For further details on how to utilise the window submenu, refer to [H Help] within that menu.

Specify another window ?

Answering yes (<Y>) allows a further window to be specified. No (<N>) is used to indicate that all the windows have been specified.

Centroid at Constant offset from mean, Multiple of standard deviation from mean or Fixed threshold ?

The centroid is evaluated relative to some threshold. Depending on a later choice, the centroid of either MAX(0,intens-iThreshold) or MAX(0,iThreshold-intens) is used. The threshold may be either fixed for all the windows (<F>), or calculated as an offset from the mean intensity for each window (<O>).

Centroid Greater than or Less than threshold ?

The response to this choice determines if the centroid is considered for regions with an intensity greater than (<G>) or less than (<L>) the threshold. If greater than (<G>), then MAX(0,intens-iThresh) is used, while if less than (<L>), MAX(0,iThresh-intens) is used when evaluating the centroid.

{If Constant offset from mean}

Constant offset from mean intensity ?

The threshold used for the centroid calculation will be the Mean intensity for the window plus or minus some constant intensity. This constant is specified by the current entry. The threshold evaluated may be different for every window in every buffer processed.

{If Multiple of standard deviation from mean}

Number of standard deviations from mean (-ve for below, +ve for above) ?

The threshold used for the centroid calculation will be the Mean intensity for the window plus or minus some multiple of the standard deviation of the intensity within the window. The multiple is specified by this field. The threshold evaluated may be different for every window in every buffer processed.

{If Fixed threshold}

Threshold for centroid ?

The entry specified here determines the fixed threshold to be used. This threshold is the same for all windows in all buffers being processed.

Name of output file (.DAT default extension, blank for monitor) ?

The mean and standard deviation of the intensity and the position of the centroid for each window will be written to the file specified by this entry. If no file name is specified, the data will be written on the computer monitor. If no extension is given to the file name, .DAT will be assumed.

The file contains data about the windows used in terms of comments (lines starting with a # character) and one line of data for each window in each image. These data lines contain the following information:

           Buffer                  Buffer used at the source for this line
           Window Number           Window number within the buffer. Details
                                   of window location given in comment at
                                   start of file
           Threshold               The threshold used to discriminate the
                                   centroid
           Average                 Mean intensity for the whole window
           StdDev                  Standard deviation of the intensity for
                                   the whole window
           iCentroid0              Vertical pixel coordinate for the centroid
                                   of the area satisfying the threshold
                                   criteria
           jCentroid0              As for iCentroid0 but in the horizontal
           iCentroid1              Vertical pixel coordinate for the centroid
                                   of the volume (i.e. weighted by P' where
                                   P' is the intensity relative to the
                                   threshold)
           jCentroid1              As for iCentroid1 but in the horizontal
           iCentroid2              Vertical pixel coordinate for the centroid
                                   weighted by P'^2.
           jCentroid2              As for iCentroid2 but in the horizontal
           iCentroid3              Centroid weighted by P'^3
           jCentroid3              Centroid weighted by P'^3
           iCentroid4              Centroid weighted by P'^4
           jCentroid4              Centroid weighted by P'^4
           iCentroid5              Centroid weighted by P'^(1/2)
           jCentroid5              Centroid weighted by P'^(1/2)
           iCentroid6              Centroid weighted by P'^(1/3)
           jCentroid6              Centroid weighted by P'^(1/3)
           iCentroid7              Centroid weighted by P'^(1/4)
           jCentroid7              Centroid weighted by P'^(1/4)
           xCentroid0              x coordinate of area centroid in world
                                   units
           yCentroid0              y coordinate of area centroid in world
                                   units
           xCentroid1              x coordinate of volume centroid in world
                                   units
           yCentroid1              y coordinate of volume centroid in world
                                   units
           iCentroid2              x centroid weighted by P'^2
           jCentroid2              y centroid weighted by P'^2
           iCentroid3              x centroid weighted by P'^3
           jCentroid3              y centroid weighted by P'^3
           iCentroid4              x centroid weighted by P'^4
           jCentroid4              y centroid weighted by P'^4
           iCentroid5              x centroid weighted by P'^(1/2)
           jCentroid5              y centroid weighted by P'^(1/2)
           iCentroid6              x centroid weighted by P'^(1/3)
           jCentroid6              y centroid weighted by P'^(1/3)
           iCentroid7              x centroid weighted by P'^(1/4)

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DigImage User Documentation

Stuart Dalziel, last page update: 19 February 1996