Re: Integrated Density and Image Scale

Posted by lechristophe on Mar 31, 2008; 4:03pm
URL: http://imagej.273.s1.nabble.com/Integrated-Density-and-Image-Scale-tp3696720p3696722.html

I'm not sure I understand.
If the ID is about "samples" (what are samples ?) and not pixels, and the
number of samples is the same in a scaled and unscaled image, then why is
the ID output by ImageJ different for the same image before and after
scaling ?

christophe

On Mon, Mar 31, 2008 at 5:57 PM, Gabriel Landini <[hidden email]>
wrote:

> On Monday 31 March 2008 16:16:18 Christophe Leterrier wrote:
> > I have a question about the "Integrated Density" measurement. In the
> ImageJ
> > docs it is stated:
> > *"Integrated Density* - The sum of the values of the pixels in the image
> or
> > selection. This is equavalent to the product of *Area* and *Mean Gray
> > Value* ."
> > This is fine for unscaled images, where the area is expressed in pixels.
>
> > But what about scaled images ?
>
> The ID is about samples, not area. The number of samples in a scaled image
> is
> the same than in a non-scaled image.
>
> The integrated density is calculated as the sum of all the sample values.
>
> This happens to be the same as area*mean density because the mean density
> is
> calculated as the sum of all the samples divided the number of samples.
> But
> to calculate the mean density you have first to compute the integrated
> density anyway, so you know this value.
>
> G.
>