http://imagej.273.s1.nabble.com/FFT-and-Inverse-FFT-problem-for-an-Electron-Microscope-Image-tp5013915p5013926.html
> Hi Michael, I am excited by your reply. Thank you for that great
> information. Can you suggest another program that can do a forward
> transform ? I tried Image Magick but I am struggling to install it
> but I could persevere ! Thanks to your advice I tried the “Complex
> Fourier Transform” in ImageJ which worked. However, I found I do need
> to swap the quadrants as you suggest. Can you suggest how I might
> achieve this please ? Also is there a way of saving the information
> in 16 bit as the subsequent program only seems to read this. I really
> feel I have progressed thanks to your help. Thank you once again.
> Mark
>
>
>> On 6 Aug 2015, at 10:29, Michael Schmid <
[hidden email]>
>> wrote:
>>
>> Hi Mark,
>>
>> if you have a program (other than ImageJ) that can do a back
>> transform, for sure it can also to the forward transform, so why
>> not open the input image and do the FFT in that program?
>>
>> Otherwise, in the FFT options you can select 'Complex Fourier
>> Transform'. These data include all the information, so in principle
>> you could transform them back. Then you just need a program that
>> can read 32-bit float tiffs (or 32-bit raw data) and do the inverse
>> transform based on the complex amplitudes. You might need to swap
>> quadrants if the external program wants to have the origin in the
>> corner, not the center.
>>
>> Michael
>> ________________________________________________________________ On
>> Aug 6, 2015, at 10:15, Rosenberg, Mark F wrote:
>>
>>> Hi Michael,
>>>
>>> I am so grateful for your detailed reply and the time you have
>>> taken with this.
>>>
>>> Can you suggest another way in Image J (which does not sound
>>> possible based on your reply) or alternative program for
>>> saving the FFT so I could transform it back please (apologies
>>> since this is an Image J only board )?
>>>
>>> This would be a great help to me .
>>>
>>> Thank you in advance.
>>>
>>> Mark
>>>> On 6 Aug 2015, at 08:48, Michael Schmid
>>>> <
[hidden email]> wrote:
>>>>
>>>> Hi Mark,
>>>>
>>>> this is a restriction of the way how FFTs are handled in
>>>> ImageJ.
>>>>
>>>> What you see as an image is not the FFT but an 8-bit version of
>>>> the power spectrum with logarithmic grayscale and pixel values
>>>> 0 and 255 omitted (reserved for filtering/masking). This
>>>> information is not sufficient for an inverse transform. The FFT
>>>> (actually an FHT) is a hidden property of the image, not
>>>> visible for the user.
>>>>
>>>> If you save the image as "FFT of..." it actually saves the FFT
>>>> (strictly speaking, the FHT), not the displayed image, and
>>>> recovers the displayed image from the FHT data. You may notice
>>>> that any modifications to the displayed image (e.g. by painting
>>>> on it, cropping, etc.) are not saved, you will always get what
>>>> 'Redisplay power spectrum' would show you. If you save it under
>>>> a different name, ImageJ assumes that you want to save the
>>>> displayed image (including any modifications by the user), not
>>>> the FHT.
>>>>
>>>> If you want to do any analysis or further processing of FFTs in
>>>> a different program, apart from measuring peak positions etc.,
>>>> you need a quantitative relationship between the pixel value
>>>> and the power spectrum. You get this when you select 'Raw Power
>>>> Spectrum' in the FFT options. Nevertheless, also the power
>>>> spectrum is insufficient for the inverse transform because the
>>>> it contains only the amplitude (squared), not the phase of the
>>>> Fourier components.
>>>>
>>>> To summarize, if you want to do further processing on an FFT in
>>>> ImageJ, save it as "FFT of..." as .tif or .zip, but beware that
>>>> modifications of the displayed image will get lost. For
>>>> analysis in other programs, save the power spectrum, but you
>>>> won't be able to transform it back.
>>>>
>>>> Michael
>>>> ________________________________________________________________
>>>>
>>>>
>>>>
>>>>> I would be so grateful for any direction to this problem I
>>>>> have encountered with Image J please.
>>>>>
>>>>> I am using OS X 10.10.3 and Image J 1.50 a.
>>>>>
>>>>> If I open an Electron Microscope Image in Image J and
>>>>> generate an FFT and then save the FFT as “FFT of
>>>>> IMAGENAME” in tif or zip format, reopen the FFT in Image J
>>>>> and do an Inverse FFT I can regenerate the original image as
>>>>> expected.
>>>>>
>>>>> However, if I rename “FFT of IMAGENAME” to any other name
>>>>> but exclude “FFT of ” in the filename I cannot do an
>>>>> Inverse FFT and if I do an FFT the Image is "lower
>>>>> resolution” .
>>>>>
>>>>> I have looked at the Info for FFT and all I can see is a
>>>>> change in ID number from -79 to -80 and a change in “Screen
>>>>> Location” coordinates. I don’t know how to edit these.
>>>>>
>>>>> Does anyone have any suggestions how to get round this
>>>>> renaming problem please because I would like to use the
>>>>> filename in a subsequent program which requires a different
>>>>> format ?
>>>>>
>>>>> Thank you for your help.
>>>>>
>>>>> -- ImageJ mailing list:
http://imagej.nih.gov/ij/list.html>>>>
>>>> -- ImageJ mailing list:
http://imagej.nih.gov/ij/list.html>>>
>>> -- ImageJ mailing list:
http://imagej.nih.gov/ij/list.html>>
>> -- ImageJ mailing list:
http://imagej.nih.gov/ij/list.html>
> -- ImageJ mailing list:
http://imagej.nih.gov/ij/list.html>