1D Power Spectrum

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This option evaluates the one-dimensional power spectra for the rows or columns of an image within a window. The logarithm of the power spectra are then displayed graphically with intensity corresponding to correlation.

Power spectrum of which buffer ?

This entry selects the buffer containing the image to be correlated. Any valid buffer may be used. The buffer chosen will then be displayed while window selection takes place.

Power spectra on Window or whole Screen ?

The 1D FFT may be evaluated for a window or the entire screen. If the region selected is not 2^n pixels, then the data will be padded out to 2^n with a linear function connecting the intensities on the two boundaries of the window.

{If window selected}

Window Selection: Region to calculate power spectra for

If a window is selected for the power spectra, then the Window Selection submenu is produced to enable specification of the required window. For more information on the window selection submenu, refer to [H Help] within this submenu.

Power spectra in Horizontal or Vertical direction ?

The power spectra may be generated for all the lines (<H>) or all the columns (<V>) within the selected window. If functions for both lines and columns are required, then it is necessary to invoke this facility twice.

Display the log of the power spectra on which buffer ?

The buffer specified here will be made the current output buffer and the results of the power spectra calculations are displayed on it with intensities representing the log of the power. The mean spectrum for the window is displayed in row or column zero.

Intensity for the zero wave number power ?

The power of the zero wave number component will be displayed with the intensity specified here.

Scale factor for intensities ?

This factor affects the scale with which the power at the various wave numbers is displayed. The displayed intensity is given by

        I = Zero + Scale(log(P) - log(P0))

where I is the intensity, Zero is the value entered at the previous prompt, Scale is the value entered at this prompt, P the power at any wave number and P0 the power at wave number zero.

Write mean power spectrum to what file (.DAT default extension; Blank to suppress) ?

If a file name is specified here, then the mean power spectrum for the specified window will be written to it for use by other programs.

Message:
Evaluating power spectra...

Errors, Warnings and Messages

Error Message: Unable to open output file

The specified output file for the Power Spectrum data could not be opened.

Parent menu

Main Menu

DigImage User Documentation

Stuart Dalziel, last page update: 19 February 1996