Posted by
Cammer, Michael on
URL: http://imagej.273.s1.nabble.com/Area-and-pixel-count-in-Photoshop-vs-ImageJ-tp5013084p5013101.html
We just has a problem yesterday where were getting odd area measurements until we realized that some pixels were set the NaN so they weren't being counted.
Check this?
=========================================================================
Michael Cammer, Microscopy Core & Skirball Institute, NYU Langone Medical Center
Cell: 914-309-3270 ** MY OFFICE HAS MOVED TO SKIRBALL 2nd FLOOR, Back right **
http://ocs.med.nyu.edu/microscopy &
http://microscopynotes.com/-----Original Message-----
From: ImageJ Interest Group [mailto:
[hidden email]] On Behalf Of Gabriel Landini
Sent: Tuesday, June 09, 2015 4:05 AM
To:
[hidden email]
Subject: Re: Area and pixel count in Photoshop vs ImageJ
On Monday 08 Jun 2015 16:04:44 you wrote:
> Here are results between Photoshop and ImageJ:
>
> In Photoshop, the measurement log shows that the Area of a 100x100
> circle is 5720. In my histogram, it reads "Pixels: 5640 pixels." The
> measurement scale is set to 1 pixel = 1 pixel.
>
> My project involves counting the number of green pixels in an image
> and dividing that number by the total number of pixels in the ROI, in
> order to get the percentage of vegetation. The number shown in the
> histogram of Photoshop next to Pixels is the value I've been using as
> the total number of pixels. Since starting to look into ImageJ, I'm
> worried that this method is not accurate.
>
> In ImageJ, I removed the scale and get the correct area of 7860.
>
> I am hoping to switch over from using Photoshop to ImageJ, but I need
> to first understand why the numbers I get in Photoshop are so different.
Most likely PS is not strictly counting pixels (some area algorithms measure , for example, the area inside the boundary pixels), or your image was calibrated or PS interpolates the boundary.
IJ is correct, I also get 7860 "in number of pixels", but the area inside the circle I get 7719 "pixels squared "according to the Freeman chain encoding algorithm implemented in Particles8.
There are more ways of counting lengths and areas to compensate for the discretisation of the lattice and also various ways of deciding what is the boundary of an object.
They are not wrong, it just depends what definitions you use.
Cheers
Gabriel
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