[Insight-users] Definition of Image Origin

[Didier Rajon]

Hi Jim, thanks for your answer.
I tried to log on the bug tracker with my email address and password, 
but it refused my connection. Do I need to subscribe to a specific 
list?  I'm currently in the insight-users list only.

Thanks,

Didier.

Miller, James V (Research) wrote:

>Didier, 
>
>I think the origin should be shifted when writing an image whose start 
>index in NOT [0,0,0].  Like you said, the readers do not have access to
>the region start index and assume that it is [0,0,0].
>
>Can you log an entry in the bug tracker?  You can paste the contents
>of your email message as the body of the bug description.
>
>Thanks
>Jim
>
>
>
>-----Original Message-----
>From: insight-users-bounces+millerjv=crd.ge.com at itk.org
>[mailto:insight-users-bounces+millerjv=crd.ge.com at itk.org]On Behalf Of
>Didier Rajon
>Sent: Tuesday, October 25, 2005 8:49 AM
>To: Luis Ibanez
>Cc: insight-users at itk.org
>Subject: Re: [Insight-users] Definition of Image Origin
>
>
>Thanks Luis for your answer.
>
>I do have a little concern about one filter.  That's the ImageFileWriter.
>Since the index is not saved with the image in most cases, should the 
>filter shift the origin to the first pixel of the dataset before writing 
>the image so that the ImageFileReader can assume an image index of (0,0) 
>when it reads the image.
>
>If I do the following:
>  1) read a vtk file using itk::ImageFileReader
>  2) crop the image by one pixel using itk::ExtractImageFilter
>  3) write the result into a vtk file using itk::ImageFileWriter
>  4) read the file just writen in step 3) using itk::ImageFileReader
>then, my image is shifted by one pixel.
>
>I also use VTK and they do shift the image origin before they save the 
>image into a file.
>
>Thanks,
>
>Didier.
>
>
>Luis Ibanez wrote:
>
>  
>
>>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.
>>>
>>>
>>>
>>>      
>>>
>>
>>    
>>
>
>  
>

-- 
Didier Rajon
Department of Neurological Surgery
University of Florida
MBI, L2100 PO Box 100265
Gainesville, FL, 32610-0265
Tel: (352) 294 0144
Fax: (352) 392 8413