Counting Pixels within ROI

Previous Topic Next Topic
 
classic Classic list List threaded Threaded
2 messages Options
Reply | Threaded
Open this post in threaded view
|

Counting Pixels within ROI

Andrew Sanchez
I am trying to understand how analyze > measure works.

I have gone to analyze > set scale and clicked "click to remove scale"

My goal is to simply count all the pixels within a circular ROI.  Should
this number be the Area within the results after going to after analyze >
measure?

I am confused because when I make a selection in Photoshop, I get one
number.  When I make a selection in ImageJ, I get another.  I know this is
an incredibly simple task, but I don't see where to find the number of
pixels within an ROI.

I need to do this on hundreds of images, so a way to generate a list of
this measurement so that I can past it into a spreadsheet would be great
too.


--
Thank you,
Andrew Sanchez
Lab Assistant
Center for Ecosystem Science
Northern Arizona University

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html
Reply | Threaded
Open this post in threaded view
|

Re: Counting Pixels within ROI

Rasband, Wayne (NIH/NIMH) [E]
> On Jun 5, 2015, at 5:23 PM, Andrew Sanchez <[hidden email]> wrote:
>
> I am trying to understand how analyze > measure works.
>
> I have gone to analyze > set scale and clicked "click to remove scale"
>
> My goal is to simply count all the pixels within a circular ROI.  Should
> this number be the Area within the results after going to after analyze >
> measure?

For unscaled images, the number of pixels is shown in the “Area” column of the Results table.

> I am confused because when I make a selection in Photoshop, I get one
> number.  When I make a selection in ImageJ, I get another.  I know this is
> an incredibly simple task, but I don't see where to find the number of
> pixels within an ROI.

You can easily verify that imageJ is counting the pixels correctly by measuring a circular selection of a known size. When I Measure a 100 pixel diameter selection created with the Oval selection tool I get an area of 7860, very close to the theoretical area of 7853.98 (Pix50x50). Hold the shift key down when creating the selection to constrain it to being circular. As you create the selection, the width and height (diameter) are displayed in the status bar.

-wayne

> I need to do this on hundreds of images, so a way to generate a list of
> this measurement so that I can past it into a spreadsheet would be great
> too.
>
>
> --
> Thank you,
> Andrew Sanchez
> Lab Assistant
> Center for Ecosystem Science
> Northern Arizona University

--
ImageJ mailing list: http://imagej.nih.gov/ij/list.html