Re: measurements using MRI jpg images

Posted by Gabriel Landini on Oct 16, 2006; 9:25am
URL: http://imagej.273.s1.nabble.com/measurements-using-MRI-jpg-images-tp3701304p3701308.html

On Monday 16 October 2006 03:03, John Dufton wrote:
> I think this is the problem.  the images i have lack the calibration.

Hi,
Even if the images were calibrated, when the image is jpeg compressed, your
pixel values are not the original ones and you will get inconsistent results.

> And thanks to everyone else regarding the use of jpg images for measuring.
> Is there is a way to convert these jpg to dicom or is that not possible?

No, unfortunately the jpeg compression is one way. When encoding, it throws
away the data that is not very obvious to the eye (but it is very obvious to
any imaging procedure). That is how it achieves small file sizes.

The real data is gone forever and one is left with something that "looks like
the original" and takes less space (which is good for the web and the
occasional photo album, but not for doing any quantitative analysis).

You should be better off by converting your dicom images to tiff or png.
Sure one can specify no compression in a jpeg file, so it saves all the data,
but why to use uncompressed jpeg format, when tiff and png can do non-lossy
compression if necessary?

Cheers,

Gabriel