FFT Power Spectrum Question: RGB vs 8-bit stack

Posted by Jack Hogan on Jul 27, 2013; 2:10pm
URL: http://imagej.273.s1.nabble.com/FFT-Power-Spectrum-Question-RGB-vs-8-bit-stack-tp5004177.html

Hello folks,

Can any of you Imagej experts illuminate a noob as to why the FFT Power
Spectra of two image types of the exact same image look so different?
 Specifically, referring to the attached image, the top row is the 8bit RGB
rendition of a raw file with minimal demosaicing and its FFT.  The bottom
row is the same RGB 8 bit rendition but after having been 'stacked' through
Image/Color/MakeComposite and an FFT generated for each color slice.

How does Imagej's FFT algorithm combine the separate RGB channels to come
up with its power spectrum? And why is it so different from the individual
channels'?

Thank you for your help.

Jack

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