Re: About sortings errors in MaximumFinder.java

Posted by José on Aug 05, 2014; 8:17pm
URL: http://imagej.273.s1.nabble.com/About-sortings-errors-in-MaximumFinder-java-tp5009020p5009038.html

Thanks for your answer,

I keep looking at the source code and other questions arise:

- Could you explain why the threshold is bringed down in line 381?
( threshold -= (globalMax-globalMin)*1e-6; )

- Also, could you explain why the maxSortingError is computing according to
the formula in line 392?
( maxSortingError = 1.1f * (isEDM ? SQRT2/2f : (globalMax-globalMin)/2e9f);
)

Thanks again.
José




2014-08-04 12:35 GMT+02:00 Michael Schmid <[hidden email]>:

> Hi José,
>
> this really goes into the details of the MaximumFinder...
>
> The MaximumFinder starts be sorting the maxima by descending value. For
> speed, this is done with 64-bit integers with the value encoded in the 32
> most significant bits and the x, y coordinates encoded in the least
> significant bits.
> The reason for the "maxSortingError" is that sorting the maxima is done
> with 32-bit integer accuracy. This might be insufficient for floating point
> images in some cases, so one has to care about cases where maxima with
> equal 32-bit values have actually different pixel values.
>
> For ByteProcessors and ShortProcessors, the maxSortingError is set to zero
> in
>  public ByteProcessor findMaxima(ip, tolerance, threshold, outputType,
> excludeOnEdges, isEDM)
>
> Having maxSortingError=0 for byte&short data should be fine unless there
> is a very strange pixel value calibration, where the difference between two
> pixel values is well below 10^-9 of the total range of pixels (Find Maxima
> uses calibrated pixel values).
>
>
> Michael
> ________________________________________________________________
> On Aug 2, 2014, at 19:21, José wrote:
>
> > I am taking a look to the MaximumFinder implementation in ImageJ 148t
> > (source code available in http://pastebin.com/wRrZqXiE ) trying to
> > understand the function analyzeAndMarkMaxima(), and I have some questions
> > about it:
> >
> > - How is the value of maxSortingError computed? (line 392) Could you
> > explain that computation?
> >
> > - Why is the condition in the if in line 569  "v2 > v0 +
> maxSortingError"?
> > Could it be "v2 > v0"?
> >
> > - Is it possible for sorting errors to happen in ByteProcessor?
> >
> > Thanks.
> >
> > José Díaz de Greñu
> >
> > --
> > 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