Re: 1D Fourier transform in macro

Posted by Ludovic Pinier on Sep 25, 2014; 7:00am
URL: http://imagej.273.s1.nabble.com/1D-Fourier-transform-in-macro-tp5009727p5009753.html

Herbie,

the pictures I work with are 16bits unsigned grey level from a CT machine (raw format). No color.
And using a Fourier transform is the method described in the standard applying to CT I use (ASTM E-1695). This standard also prevents to remove the mean or alter the contrast/brightness. To be standard-compliant, profile (the "Edge Spread Function") is mandatory. You are only allowed to frequency-filter it, and remove aberrant points. Even the Fourier transform sampling has to be compliant with the standard criteria.
Concerning the Fourier transform, I am used to manipulate time-frequency transforms, but not to deal with the programming aspects.
Last, my reason is that the tool built in the machine is not accurate.
And the "slanted edge method" plugin is inappropriate for the geometry of my targets (which are also defined according to the standard: material, shape and size).
The standard requires a line profile, and the slanted edge produces an integration of the profile along the edge.
I could use this plugin with 1pixel-wide areas, but ,that means I need to rotate the image; and even if is an as-accurate-as-possible transformation, it is an interpolation that produces a calculated image. It is not the direct capture from the sensor anymore. That is also the reason why the slanted edge method was introduced in the ISO12233. But unfortunately, the target definition in this standard is inappropriate for my use.

I know your suggestions could definitely help, but they don't apply to my need.

Best regards,
Ludovic

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