http://imagej.273.s1.nabble.com/Handling-signed-and-unsigned-16-bit-images-tp3693185p3693188.html
This is helpful. I am comparing a pixel value to min/max cutoffs and
> Hi Mike,
>
> it depends what you want.
>
> In ImageJ, 16-bit images are taken as unsigned by default; thus all
> reading of pixel data requires code like this:
> int value32bit = pixels[pixelPointer]&0xffff;
> where
> short[] pixels = (short[])ImageProcessor.getPixels();
>
> Signed 16-bit images are simply unsigned data with a calibration
> table that maps pixel value 0 to -32768 and
> 32768 to 0. To simplify the code, actually any calibration table that
> maps 0 to -32768 (irrespective of the further values) is taken as an
> indication of signed 16-bit data.
>
> For most filter operations, it makes no difference whether the data
> are signed or unsigned.
> For math operations such as multiply, the operation depends on the
> calibration table as stated above.
>
> For analysis of pixel values, you can use
> ImageProcessor.getPixelValue; it gives the calibrated values and thus
> you get the correct values for signed data. Also
> ImageProcessor.putPixelValue works with both signed and unsigned 16-
> bit images.
>
> When writing a PluginFilter, ImageJ will automatically take care that
> an ImageProcessor gets the correct calibration from its ImagePlus. In
> a Plugin, you may have to care about this separately, especially when
> processing stacks.
>
> The CONVERT_TO_FLOAT flag of a PlugInFilter does not take calibration
> into account; thus it always takes the data as unsigned 16 bit.
>
> Hope this helps,
>
> Michael
> ________________________________________________________________
>
> On 24 Mar 2009, at 14:01, Burger Wilhelm wrote:
>
>> Right, Java has no unsigned types - but it is only a matter of a
>> few bit operations to treat 16-bit words as either signed (default)
>> or unsigned. However, I don't think there is any way to mark a
>> ShortProcessor as "signed", so a plugin cannot distinguish between
>> unsigned and signed images (unless you make assumptions).
>>
>> --Wilhelm
>>
>>
>>
>>
>>> -----Original Message-----
>>> From: ImageJ Interest Group [mailto:
[hidden email]] On
>>> Behalf Of Reinhard Mayr aka Czerwinski
>>> Sent: Tuesday, March 24, 2009 1:43 PM
>>> To:
[hidden email]
>>> Subject: Re: Handling signed and unsigned 16-bit images
>>>
>>> Mike,
>>>
>>> I once extended the AVIReader for a certain kind of 16bit
>>> AVIs
>>> (
http://rsb.info.nih.gov/ij/plugins/download/AVI_Reader.java).
>>> Maybe you find something useful there.
>>>
>>> As far as I remember, the major problem is that Java does not
>>> know unsigned data types.
>>>
>>> Hth & all the best!
>>>
>>> Reinhard.
>>>
>>> -------- Original-Nachricht --------
>>>> Datum: Tue, 24 Mar 2009 11:15:15 +0000
>>>> Von: Michael Doube <
[hidden email]>
>>>> An:
[hidden email]
>>>> Betreff: Handling signed and unsigned 16-bit images
>>>> Hi all
>>>>
>>>> After a bit of googling and hacking and tying myself in
>>> knots, I have to
>>>> ask the list how people write plugins that can elegantly
>>> handle both
>>>> signed and unsigned 16-bit images?
>>>>
>>>> I had a play with
>>>
http://rsbweb.nih.gov/ij/plugins/converter.html, and
>>>> will continue in this sort of direction unless there's a
>>> known better
>>>> way to do it.
>>>>
>>>> Cheers
>>>>
>>>> Mike
>>> --
>>> Psssst! Schon vom neuen GMX MultiMessenger gehört? Der kann`s
>>> mit allen:
http://www.gmx.net/de/go/multimessenger01>>>