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| File Edit Options Process Analyze Video Macros Stacks SEM SPM Windows Help |
Sharpen Shadow Find Edges Rank Filters Dither Convolve PlugIn Filters
Enhance Contrast Equalize Fix Colors Differential Curvature Unsharp Mask Hough Transform |
FFT Inverse FFT Display Power Spectrum Swap Quadrants Select Largest Square Select Longest Line Autocorrelation Make LEED into FFT Inverse FFT of LEED |
The commands in
this submenu support frequency domain display, editing and processing.
They use a real 2D Fast Hartley Transform (FHT) routine contributed by
Arlo Reeves, the author of ImageFFT.
For more information about the FHT and ImageFFT, see the ImageFFT documentation, example
images and Arlo's thesis, available from the nih-image_spinoffs
directory of the NIH Image
web site.
The transformed frequency domain images created by the FFT command are stored as 32-bit real images. The name in the window's title bar is enclosed in angle brackets to indicate that the window includes a real image. The only commands in NIH Image that currently recognize real images are FFT, Inverse FFT, Redisplay Power Spectrum and Image Math. All other commands "see" only the 8-bit power spectrum. The Image Math command supports arithmetic operations on the real images created by the FFT command. You can use it for multiplication (convolution), division (deconvolution) and conjugate multiplication (crosscorrelation and autocorrelation) of frequency domain images. |
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Steve Barrett November 2014 |
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