[Insight-users] Definition of Image Origin

[Luis Ibanez]

Hi Didier,

The origin is associated with the pixel of Index (0,0).

However, as you pointed out, an image may actually start
in an index (15,25), and therefore the origin may be
"outside" of the sampling grid of the image.

That's fine because at the end, the purpose of the origin
is to be able to compute the coordinates of every pixel
in the sampling grid of the image.

Note that not all filters may be doing the right thing
when managing images that have a Start index different
from (0,0).  If you find any suspicious behavior please
let us know, so we can check if this is the result of a
bug in a particular filter.


   Thanks


      Luis



------------------
Didier Rajon wrote:
> Hello,
> I'm a little confused about the definition of the Image Origin.
> According to the definition that I found in the ITK Software Guide - 
> Second Edition (August 30, 2005); p 40: "the image origin is associated 
> with the coordinates of the first pixel of the image".
> On page 224 of the same documentation I found Eq. (6.20) that suggests 
> that the origin is associated with the coordinates of the pixel indexed 
> by (0, 0).
> On page 234 of the same documentation I found an expression to calculate 
> the image center and that suggests that the origin is associated with 
> the coordinates of the first pixel of the image, whatever the index of 
> the image.
> So, if my image has a LargestPossibleRegion().GetIndex() equal to 
> (10,10), is my image origin the coordinates of the pixel indexed by 
> (10,10) (my first pixel in this case) or the coordinates of the pixel 
> indexed by (0,0) (which is out of my dataset in this case)?
> Thanks,
> 
> Didier.
> 
> 
>