Posted by
Gabriel Landini on
Mar 11, 2016; 4:43pm
URL: http://imagej.273.s1.nabble.com/Threshold-bug-tp5015854p5015857.html
On Friday 11 Mar 2016 16:05:52 you wrote:
> Here's an image showing what I mean:
> [image: Inline image 1]
> I've drawn a black cross over the pixel I'm looking at. You can see the
> value is 262.73, which is above the threshold but the pixel appears red!
> Are you saying it's a rounding error from mapping the 32bit image to 8bit?
Hi,
There is no practical way to handle and display a histogram of floating point
values. IJ bins the range into an 8 bit histogram (that is 256 bins) , so each
bin will contain a range of values. That is what you see.
We cannot expect to have a slider capable of going through every possible
value from -2586.34 to 260.45.... Or be able to show it in a histogram... How
large should that be?
You could convert your image to 8bits if you want to see exactly the red
pixels where they will threshold, but that is not much different from what you
are doing now as that involves you re-binning the image.
Or you could convert the 32 bit to 16 bits and use the Auto Threshold plugins
in my page (also included in the Fiji version) which use a 16bit histogram (I
think the built in IJ thresholder bins the 16 bit images too).
When you set a value manually using the Set dialog, that would be exactly
thresholded at that value as far as I know.
Hope it helps
Gabriel
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