Re: Image compression

Posted by Aryeh Weiss on Dec 23, 2005; 4:54am
URL: http://imagej.273.s1.nabble.com/Image-compression-tp3704130p3704134.html

Yong Zhang wrote:

> Hi, John,
>
> If the image compression is "lossless", then the measurements will not be
> affected since no information is lost during the compression. The lossless
> compression is a good way to store/transfer large dataset without any loss
> of the useful information. But you have to make sure that the compression
> is really "lossless" when using any software, because one format can be
> either lossless or lossy. For example, JPEG format can be lossless or
> lossy. So you must select lossless mode when saving your original image
> into another format. If your software does not provide lossless/lossy
> selection when saving images, then you'd better switch to another software
> which has the selection.
>

That's the good news. The bad news is that you may only see up to 50% size
reduction with lossless compression (unless your images are thresholded or have
large uniform areas), but if you cannot tolerate any discrepencies in you
images, then that's what you get.

If you plan to filter out point noise (eg, with a median filter), or to do any
smoothing, then you should do this before lossless compression. This will
improve the compression ratio.

--aryeh
--
Aryeh Weiss
School of Engineering
Bar Ilan University
Ramat Gan 52900 Israel

Ph:  972-3-5317638
FAX: [phone]