what are the preprocessing steps to get a binary Image using OTSU?

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Hi All
I am able to get a binary image for the attached example by defining threshold manually (trial and error). However, When I use Otsu thresholding, the result is not satisfactory. What pre-prosessing would be useful before I apply OTSU for the attached Image? I also present the result when I use OTSU AS below.
Any other methods to get a binary Image are welcome.

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Image Analyst
Image Analyst il 25 Nov 2018
Try a top hat filter. See attached.
0000 Screenshot.png
  11 Commenti
engineer il 27 Nov 2018
Because I have checked the tip location manually by using imtool and compared result I have got from binary image. There are differences around 20 pixels. Even when I align them, I can see that at the end of objec is not binarized well. It is shorter than the original one.
For example, the original tip position is (373,515). The position obtained from the binary image is (355,513).
My aim is just to be as close as posible to the original location.
Image Analyst
Image Analyst il 27 Nov 2018
It looks like you're trying to find the black stuff whereas I was trying to find the bright stuff inside the black stuff, so I got rid of the last part of the loop and looped over structuring element radii to see which one give the best values. Did you try that? I did and am attaching the code and the image it makes. Pick whatever radius looks best to you. Or you could try to change the shape of the structuring element from a disk to a cross or something to see if that does better.
0001 Screenshot.png

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Image Analyst
Image Analyst il 23 Nov 2018
Modificato: Image Analyst il 23 Nov 2018
Try this:
binaryImage = imbinarize(grayScaleImage);
You can also try my interactive method in my File Exchange.
Or you can try my triangle thresholding method, attached.
You should also do a background correction on the image before using a global threshold. See attached demo.
  1 Commento
engineer il 25 Nov 2018
Hi Image Analyst
Thanks for your help. I could not implement triangle threshold algorithm unfortunately. Matlab gets busy and give an error in the end... I have tried background correction. Unfortunately, results are not satisfactory. It is so confusing for me to get a binary image from my attached image. On the other hand not having the same or even similar results ( as in manual thresholding) from another algorithms, such as OTSU...
I would appreciate if you look into my image and tell me what could be the problem.
Kind regards,

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