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