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Re: Raw versus calibrated integrated density

Posted by Michael Schmid on Oct 18, 2010; 3:21pm
URL: http://imagej.273.s1.nabble.com/Raw-versus-calibrated-integrated-density-tp3686613p3686616.html

Hi Andrew,

maybe my example has been deceiving - watts/cm2 is the intensity  
(grayscale) unit in my example.

The IntDen unit is:
  <realworld unit> * <realworld unit> * <intensity unit>

Maybe there is a better example:

Assume, you take an image of a bright spot, 10um*10um with 1 um pixel  
spacing, and all pixels having intensity = 100.

Then you get integrated density = 10 um * 10 um * 100 = 10000 um^2.

Now, scale the image so that you have 2 um pixel size. The bright  
spot will be just 5*5=25 pixels, and raw integrated density will be  
2500.
Nevertheless, scaled integrated density will still be 5*2 um * 5*2 um  
* 100 = 10000.

You can easily try this with an image of your choice and the  
"Image>Adjust>Size" function of ImageJ.

Is this explanation better?

Michael
________________________________________________________________

On 18 Oct 2010, at 16:42, IJperson wrote:

> Hi Michael.
>
> Many thanks for the reply.
> To clarify, I am not referring to greyscale calibration. Lets  
> assume I am
> just interested in the intensity of the pixels as they appear, with  
> no extra
> scaling.  My confusion lies with different integrated intensities  
> (IntDen
> and RawIntDen) over spatial calibration.
>
> The example you present with Watts is helpful.  So the integrated  
> density
> has units:
>  cm * cm * W/cm^2 = watts.  I.e. The spatial units disappear.
>
> So the calibrated (IntDen) has units:
> <realworld unit> * <realworld unit> * <intensity unit>  /  
> <realworld unit>^2
> =<intensity unit>
>
> and the uncalibrated (RawIntDen):
> <pixel unit> * <pixel unit> * <intensity unit>  / <pixel unit>^2
> =<intensity unit>
>
> I.e. both have the same unit, which appears to be independent of a  
> spatial
> dimension. So should both therefore have the same value?
>
> I expect I am still misunderstanding something, but this is a very  
> helpful
> discussion.
>
> Many thanks
> Andrew