http://imagej.273.s1.nabble.com/Autocorrelation-using-Fourier-tp3686185p3686187.html
registration of paired, offset images. I am probably missing something
width or height of the image. Could you suggest a method to work around
> Hi Norbert,
>
> here is a rough equivalent to the core of your correlation macro using
> FFT:
>
> k100 = 100; //how far out we need the autocorrelation
> run("FD Math...", "image1=AutoCorr.tif operation=Correlate
> image2=AutoCorr.tif result=Result do");
> width = getWidth();
> run("Divide...", "value="+(width*width)); //FD Math gives sum over all
> pixels; convert to mean
> half = width/2; //origin is at the center
> makeLine(half, half, half+k100, half);
> run("Plot Profile");
>
> It won't be 100% exact because the FFT version extends the image
> assuming periodic boundary conditions, not using a value of zero as
> the 'translate' command in your macro.
> This won't matter for your test image which has a rather large border
> with zero value.
> If periodic boundary conditions are a problem, simply enlarge the
> image to the next power of 2 with zero background.
>
> Hope this helps.
>
> Michael
> ________________________________________________________________
>
>
> On 13 Dec 2010, at 23:19, Norbert Vischer wrote:
>
>> Hello all,
>>
>> I created a test macro that performs 1D autocorrelation.
>> It runs well in a few seconds, but I wonder if the speed can be
>> improved by Fourier techniques for larger data sets.
>>
>> The macro first creates a test image that is randomly covered with
>> white horizontal lines with a mean length of 20 pixels. The image is
>> then periodically multiplied with a horizontally shifted copy, so I
>> get the autocorrelation plot from which I can derive the mean line
>> length. The output looks like this:
>>
>> Simulated Length = 20.17
>> Measured Length = 20.06
>>
>> Later in reality, the white lines will represent the fluorescent
>> duration of molecules, and the data set will be much larger.
>> I doubt that a native plugin will do the same thing much faster, but
>> has anyone a suggestion how to use Fourier techniques?
>>
>> My demo macro can be downloaded from:
>>
http://simon.bio.uva.nl/objectj/GenericMacros/AutoCorrelation/AutoCorrelation-2.txt
>>
>>
>>
>> Norbert Vischer