[ImageJ-bugs] [Bug 938] Bug in the Intermodes algorithm of threshold

[bugzilla at fiji.sc]

http://fiji.sc/bugzilla/show_bug.cgi?id=938

Curtis Rueden <ctrueden at wisc.edu> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDSINFO
                 CC|                            |bnorthan at gmail.com,
                   |                            |ctrueden at wisc.edu,
                   |                            |g.landini at bham.ac.uk

--- Comment #1 from Curtis Rueden <ctrueden at wisc.edu> ---
Thanks for the report, and macro to reproduce!

The ImageJ 1.x implementation is in a class called AutoThresholder:

https://github.com/imagej/ImageJA/blob/v1.49h/src/main/java/ij/process/AutoThresholder.java#L176-L220

And the "Auto Threshold" implementation, which is part of Fiji, can be found
at:

https://github.com/fiji/Auto_Threshold/blob/0565751243a83688c84857475adb51ae836a843e/src/main/java/fiji/threshold/Auto_Threshold.java#L493-L541

The ImageJ 1.x implementation returns 1713 when "Dark background" is checked.
The Fiji Auto_Threshold implementation returns 525.

It was not clear to me from your bug report which algorithm you believe to be
correct, and which incorrect. However, seeing as how the minimum data value of
the entire "Neuron" sample image is 526, the value 525 seems obviously wrong to
me. So I conclude that the ImageJ 1.x result is correct, while the Fiji
Auto_Threshold result is incorrect. Right?

As an aside: there is a third implementation, recently ported from Fiji's
Auto_Thresold, in the ImageJ OPS library:

https://github.com/imagej/imagej-ops/blob/114183192d41e9dcbe0e6450512170f8a566dc6e/src/main/java/net/imagej/ops/threshold/global/methods/ComputeIntermodesThreshold.java#L58-L100

Since it was ported from Fiji's Auto_Threshold, it also suffers from this bug.

Gadea: Could you please confirm that the ImageJ 1.x code produces the correct
result, and the Fiji Auto_Threshold code an incorrect one? If so, I will fix
the bug in the two affected libraries.

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