FFT Questions

Previous Topic Next Topic
 
classic Classic list List threaded Threaded
4 messages Options
Reply | Threaded
Open this post in threaded view
|

FFT Questions

maveric_ben
Hi guys,
 I know the Data of FFT power spectra(8 bite greyscale) is in log scale. But what is the base? 2, e, or 10? or it is a variant to fit the data in 1~254?
 If I am not sure about the base and I want to get the exactly power spectra data in linear scale, what should I do? Is there such a plugin? thanks a lot!
Cheers
Ben
Reply | Threaded
Open this post in threaded view
|

Re: FFT Questions

Wayne Rasband
> Hi guys,
>  I know the Data of FFT power spectra(8 bite greyscale) is in
> log scale. But what is the base? 2, e, or 10? or it is a variant
> to fit the data in 1~254?

Log base e, then linearly scaled to 1-254.

>  If I am not sure about the base and I want to get the exactly
> power spectra data in linear scale, what should I do? Is there
> such a plugin? thanks a lot!

You can get the unscaled power spectrum by checking "Raw Power  
Spectrum" in the Process>FFT>FFT Options dialog.

-wayne
Reply | Threaded
Open this post in threaded view
|

Re: FFT Questions

maveric_ben
thanks wayne, it works! the base is about 1.1, looks like it is a variant.
Reply | Threaded
Open this post in threaded view
|

Antwort: Re: FFT Questions

Joachim Wesner
Hi,

if you do a log to a given scale and later rescale the result linearly to
another range, it´s fully equivalent to using another ("fixed" for that
image) base of the log from the start. Yet, those 1.1 will not stay the
same for other images, it actualy depends on the data in the actual image
(autoscaling!)

Better use the raw image data!!!!

JW



                                                                                                                                       
                      maveric_ben                                                                                                      
                      <benchermar@YAHO         An:      [hidden email]                                                            
                      O.COM>                   Kopie:                                                                                  
                      Gesendet von:            Thema:   Re: FFT Questions                                                              
                      ImageJ Interest                                                                                                  
                      Group                                                                                                            
                      <[hidden email]                                                                                                
                      .GOV>                                                                                                            
                                                                                                                                       
                                                                                                                                       
                      11.05.2006 19:25                                                                                                
                      Bitte antworten                                                                                                  
                      an ImageJ                                                                                                        
                      Interest Group                                                                                                  
                                                                                                                                       




thanks wayne, it works! the base is about 1.1, looks like it is a variant.
--
View this message in context:
http://www.nabble.com/FFT-Questions-t1596142.html#a4345033
Sent from the ImageJ forum at Nabble.com.



______________________________________________________________________
This email has been scanned by the MessageLabs Email Security System.
For more information please visit http://www.messagelabs.com/email 
______________________________________________________________________