as a consequence of repeated requests (most recent), I’ve released a macro-recordable ImageJ-plugin for image windowing and DC-removal.
The plugin is DCfree_Windowing.class and can be accessed from here:
The plugin requires a square-sized 32bit image of even side length and applies to it a disc-shaped window (diameter = image size) with a raised cosine slope (“Tukey”-type window). The percentage flat of the disc can be set from 0% (“von Hann”-type window) to 100% (hard-limiting window).
The mean of the windowed image values inside the window is then reduced to negligible values. All values outside the window remain zero. The reduction factor is typically better than 10^8. This kind of DC-removal of windowed images doesn’t cause any artifacts (jumps, ridges) or level shifts and can hardly be obtained by other methods.
Here is an example using a unipolar zone plate as a test image:
Please note that black is 0.0 and white is 1.0.
Please note that now black is –0.5 and white is +0.5.
The percentage flat of the window was set to 75%.
Here are the measurements from both images (no selection applied!):
I hope the plugin proves useful at least for those looking for professional-grade global/regional orientation analyses.