Antwort: Re: Image Processing Question

Posted by Joachim Wesner on
URL: http://imagej.273.s1.nabble.com/Image-Processing-Question-tp3696307p3696309.html

Hi again,

JAIN, mathematically true, but 8-Bit and 16-Bit ImageJ image format
(if not scaled) is considered unsigned, so any negative calculation result
will be clamped to zero, you need to at least convert the image to 32-Bit
- or add an appropriate offset - to retain image statistics.

JW

ImageJ Interest Group <[hidden email]> schrieb am 07.05.2008 17:48:48:

> Just answer the statistics part of your question. Adding/substracting a
> constant number to your orignal data will not change the standard
> deviation.
>
>
> Hi,
>
> here is what I do for a little plugin in Java:
>
> pic1 - pic2 = result1 --> measure --> min1 = 0
>
> (pic1 +100) - pic2  = result2 --> measure --> min2 = 53
>
> Built-in Plugins give the same results. Is ImageJ setting negative Pixel
> values to Zero, since I expected min2=100?
>
> And of course if you do image statistics stdDev (result1) and stdDev
> (result2), the results will be different. In my opinion the addition of
> an offset is required for the correct calculation of stdDev, but maybe I
> am wrong.
> Any suggestions on this issue?
> Thanks for your help!
>
> Sebi

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