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Re: Strange Threshold on an image

Posted by lechristophe on May 29, 2008; 8:41am
URL: http://imagej.273.s1.nabble.com/Strange-Threshold-on-an-image-tp3696115p3696116.html

Sorry for the bad link, the image is here :

http://ftp.espci.fr/incoming/christo/Strange_Threshold.tif

On Thu, May 29, 2008 at 10:39 AM, Christophe Leterrier
<[hidden email]> wrote:

> Dear all,
>
> I've a problem with the Auto Threshold setting with images that have
> quite a lot of saturated pixels (I know it is bad imaging, but it is
> not one of my images :) The image is available here :
>
> http://ftp.espci.fr:21/incoming/christo/Strange_Threshold.tif
>
> It is a 8-bit 1024x1024 image. If I Auto Threshold it, it sets it to
> 0-99, i.e. it detects what is OUTSIDE of the object (if I binarize,
> I've the outside of the cell at 255 and the inside at 0). To be
> consistent with non-saturated images, the threshold should be 99-255 I
> guess. The problem doesn't exist with non saturated images : if you
> divide this image by 3, the Auto Threshold detects the inside of the
> cell, not the outside (Auto Threshold sets to 41-255).
>
> Is it a rational consequence of the Auto Threshold algorithm or is it
> a bug ? I've modified my macro that batch treats images to detect
> these cases (detect and correct if the lower threshold is set to
> zero), but I wonder if this behavior has a rational explanation.
>
> Thanks for your help,
>
> Christophe
>