http://imagej.273.s1.nabble.com/measurements-using-MRI-jpg-images-tp3701304p3701307.html
I think this is the problem. the images i have lack the calibration.
>From: Gino Canessa <
[hidden email]>
>Reply-To: ImageJ Interest Group <
[hidden email]>
>To:
[hidden email]
>Subject: Re: measurements using MRI jpg images
>Date: Sun, 15 Oct 2006 20:41:28 -0500
>
>My guess would be that there is no calibration reference for the JPEG
>images
>(e.g., it is measuring pixels), whereas the DICOM images have calibration
>so
>that measurements can be converted into more useful numbers (e.g., mm).
>
>If you are just measuring pixels on both, as Gabriel said, there are
>artifacts introduced by the JPEG conversion.
>
>
>All of this assumes, of course, that by saying "jpg," you mean an actual
>JPEG, instead of a JPEG compressed DICOM. If you are using a JPEG
>compressed DICOM image, and the compression was set to lossless, there
>should be no differences.
>
>Hope this helps,
>
> Gino
>
>
>P.s., Just like to re-enforce Gabriel's mention that JPEG images should not
>be used for analysis of anything (again, barring the lossless types common
>in DICOM, et all).
>
>
>
>
>
>On 10/15/06 4:54 PM, "Gabriel Landini" <
[hidden email]> wrote:
>
> > On Sunday 15 October 2006 06:43, John Dufton wrote:
> >> I have a question regarding measurements on mri images.
> >> I have saved a number of images as jpg images. The measurements on
>these
> >> jpg images do not seem to correspond to measurements on the
>workstation.
> >
> > Hi,
> > Jpeg compressed images should not be used for serious imaging purposes.
> > The compression in the jpegs is lossy, so I guess that you may be
>measuring
> > some amount of artifacts rather than the data.
> >
> > Instead, you can save your images as Tiff or Png.
> >
> > Cheers.
> >
> > Gabriel
>
>--
>Gino Canessa
>
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