Posted by
Hening Bettermann on
Mar 25, 2015; 5:08pm
URL: http://imagej.273.s1.nabble.com/Problems-using-the-FFT-Bandpass-Filter-tp5012174.html
Hi!
I am looking for a way to extract regions of equal degrees of blur from 16 bit TIF RGB images. Bart van der Wolf has kindly guided me to ImageJ in this thread on the Luminous-landscape.com forum:
http://forum.luminous-landscape.com/index.php?topic=98885.msg808398#msg808398providing this recipe:
"to select defocused regions, you would need to use software that allows to isolate (de-)focused areas. This hints at spatial frequency separation, something that can e.g. be done with ImageJ with it's FFT Bandpass filter. Open the image and convert it to an "Image type 32-bit" version with the menu choices. Then use "Process FFT Bandpass Filter...", and use the setting from the attached image to select the focused areas. Then convert the result to "Image Type 16-bit" and save it as a TIFF or a PNG file, which then can be used in Photoshop to create a mask.
You can create a mask from the above selection and a layer filled with 50% gray, in Difference mode. Then use a Levels adjustment and a bit of blur to get the general mask, perfected with some local painting in/out."
The setting suggested for the FFT Bandpass filter was 'Filter large structure down to -1- pixels; filter small structures up to -0- pixels.'
To extract regions of increasing blur, the first value would have to be increased, then the resulting masks would have to be subtracted.
After some trial and error concerning 'out of memory' alerts, I am able to do the following:
Open the image in ImageJ. It is displayed as 3 different layers, the red layer on top.
Image > Color > Stack to RGB
Process > FFT > Bandpass filter, with 2 different settings: 1-0 and 16-0.
Image > Type > 16 bit
In ImageJ, both of the resulting images look like the complete image, just in black and white.
After saving to disk and then opening in Mac Preview or in PhotoLine, they both look all black.
I am running ImageJ 1.49 64 bit on a MacBook Pro with OSX 10.9.5 and 16 GB of RAM.
Can anybody help? - Thank you!
Hening Bettermann.
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