Re: Is it possible to measure with sub-pixel resolution?

Posted by Emmanuel Levy on May 08, 2016; 7:55pm
URL: http://imagej.273.s1.nabble.com/Is-it-possible-to-measure-with-sub-pixel-resolution-tp5016356p5016358.html

Hi Michael,

Thank you for replying.

selections (=ROIs, regions of interest) in ImageJ cannot contain something
> like half a pixel.


That is a pity - from the perspective of the GUI it appears possible to
define sub-pixel selections, which made me hopeful (
https://imagej.nih.gov/ij/docs/guide/146-10.html).

In principle, I could have imagined that the value of a pixel covered by a
selection could be weighted by the fraction of its area covered. But it's
good to know it's not a possibility, I won't look any further. If this
becomes critical we will use the size-adjustment trick you suggested.

Thanks again,

Emmanuel



A pixel is considered either inside or outside a

> selection, nothing in between.
>
> If you need better resolution for measurements, you have to increase the
> image size, Image>Adjust>Size, and use interpolation.
>
> Michael
> ___________________________________________________________________
>
> On Sun, May 8, 2016 18:15, Emmanuel Levy wrote:
> > Dear list members,
> >
> > I was wondering if there's a specific option/way to do measurements in an
> > image with sub-pixel resolution?
> >
> > I paste below macro code to illustrate what I mean. The following creates
> > a
> > 10x10 pixels image, half of which is back and the other half white. If I
> > draw a triangle that is half in the black and half in the white area,
> with
> > a total area of 1pixel, I get a mean value of 255, but I would have
> > expected 127.5
> >
> > newImage("Untitled", "8-bit black", 10, 10, 1);
> >
> > makeRectangle(5, 0, 5, 10);
> >
> > setBackgroundColor(255, 255, 255);
> >
> > run("Clear", "slice");
> >
> > makePolygon(4,5,6,5,5,6);
> >
> > run("Measure");
> >
> >
> > Does anyone know if it's possible to get 127.5?
> >
> > Thanks for your help,
> >
> > Best wishes,
> >
> > Emmanuel
> >
> > --
> > ImageJ mailing list: http://imagej.nih.gov/ij/list.html
> >
>
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>

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