Re: Measuring areas...

Posted by Rotella, Anthony M. (GRC)[] on Jun 18, 2007; 4:57pm
URL: http://imagej.273.s1.nabble.com/Measuring-areas-tp3699083p3699087.html

Oh geez. So lets say I went through a thresholded image, and just simply
counted the pixels. Is this a compatible area measurement if I wanted to
use these numbers with area calculated with the "Analyze Particle"
operation? My number seems accurate, but it would be nice to make sure
I'm not doing anything stupid. Thanks..

Tony

>-----Original Message-----
>From: ImageJ Interest Group [mailto:[hidden email]] On
>Behalf Of Gabriel Landini
>Sent: Monday, June 18, 2007 11:44 AM
>To: [hidden email]
>Subject: Re: Measuring areas...
>
>On Monday 18 June 2007 16:26:59 Christophe Leterrier wrote:
>> I would think that a pixel is
>> more a surface unit than a length unit. A 4x4 pixels square is a 16
>> pixels area, or 16 pixels^2 if you prefer.  Strictly
>speaking I'd say
>> a pixel is a square that have a 1x1 pixel dimensions, so it's also a
>> pixel^2 (I mean, for most acquistion systems, rectangular pixels do
>> exist also).
>
>Not always. A pixel may also be considered a point. Otherwise
>one could not draw/analyse lines.
>If you consider pixels to be sampling points, then a 4x4 pixel
>square has an area of 9 pixels^2 (since you count from the
>centre of the sampling points as the vertices of the polygon
>(and a square of 2x2 has an area of 1).
>There are more ways to handle areas and perimeters of polygons
>in discrete space. Because of this, Particles8_Plus plugin
>gives both the Area and the Pixels in a blob. You can have
>lots of pixels and no area.
>
>Cheers,
>
>G.
>