Posted by
Michael Schmid on
Jun 22, 2015; 4:45pm
URL: http://imagej.273.s1.nabble.com/image-summing-details-tp5013231p5013245.html
Hi Martin,
yes, the Image>Stacks>Z Project operation is very simple:
sum = sum of all pixels at a given position (no scale!)
average = sum / (number of slices in the stack)
The operation is done on raw pixel values; not taking the pixel value calibration (if any) into account.
If there is no nonlinear pixel value calibration, the average is simply the average over all pixels at a given position.
There is no scale applied to the 'Sum Slices'. Just look at the pixel values in the ImageJ status line when placing the cursor at some position of the SUM_... image or use the Pixel Inspector to see the values of the cursor position and a small neighborhood.
http://rsb.info.nih.gov/ij/docs/guide/146-19.html#toc-Subsection-19.20Michael
________________________________________________________________
On Jun 22, 2015, at 14:55, Martin Ward wrote:
> Hi Gabriel,
>
> Thanks for your reply. For my application, the images vary with a function of time (slice number) and it is the average intensity (grayscale) of a number of slices that I require. I will use the average projection type and see how I get on with that. However, having found out that there is a scale applied to the sum slices process it would be good to find out what actually happens when the average projection type is used; i.e., is it a simply pixel by pixel average or not?
>
>
> Regards,
> Martin.
>
>
>
> Quoting Gabriel Landini <
[hidden email]> on Mon, 22 Jun 2015 13:20:57 +0100:
>
>> Hi,
>> If all what you want to compute is the average of the slices, in the Z Project
>> menu, there is already an "Average" function, so no need to sum them up.
>> Cheers
>>
>> Gabriel
>>
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