Exporting FFT result like GIMP plugin

Software G'MIC
1

Hi!
I’m trying to export FFT result using this command:
GMIC Src.png -luminance --fft -append[-2,-1] c -norm. -log. -shift. 50,50,0,0,2 -output Dst.png
This is from GMIC’s examples, so it is not a complete command. What should I write to have the same result as the plugin (column of 6 images) for further processing? [question 1]

By the way, destination picture is almost black, that’s because of using FP operations. When watching in preview mode (omit -output attribute) I see values like 7.464362323235, 12.575475234 etc., of course it will be saved as very dark because no scaling to 255 is performed. How to make GMIC to save NORMAL images like plugin do? [question 2]

2

If you want to call the exact procedure that is done by the plug-in, then try this :

$ gmic image.jpg -gimp_fourier 0,1

for the FFT, and :

$ gmic imageFFT.jpg -gimp_fourier 1,1

for the invert transform.

3

Thank you very much, you’re king among people! :smiley: Looks like it is what I need.
But I have some questions:
0. Where can I read about -gimp_fourier switch? I didn’t find it @ http://gmic.eu

  1. First digit in command means direction of conversion: 0 — direct, 1 — inverse, right?
  2. Resulting image have size _orig_height_×6+2, who are these extra pixels? :slight_smile:

Thanks in advance :relaxed:

4

Yes, actually all filters in the G’MIC plug-in for GIMP are defined by their own G’MIC commands, and these commands are not documented (yet). In the plug-in, you can get the exact command invoked for a specific filter, by setting the option Output messages... to Verbose (layer name), then apply the filter. The layer name of your output image contains the G’MIC command that has been called by the plug-in. It’s easy then to reproduce exactly what the plug-in does.

So, for your first question, yes, the first command argument means direct or inverse transform, in this context.
For your second question : the extra lines added are used to store the value range of the image, so that the invert transform can manage the real floating point values of the FFT, instead of the one stored as a 8bits image.

5

Thank you again! I didn’t know about such a way of getting GMIC command :slight_smile:
I wish you the best!