Define the appropriate threshold level

Hi all, There are some images that I obtained from different levels. Like in file. Four of them have different level particles inside it. How can I define the appropriate value. Is it necessary to remove information zone from image or not? For each image ı want to define suitable value. Also there should be similar images like this Thanks.

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Answer 1

[ali]

Any suggestion. For example triangle threshold or look for histogram values. Or looking for two level segmentation which one is better?

Answer 2

[ali]

If I try random values for all images for example 0.5 for 1 and 4 image. And 0.7 for 2 and 3 image I got good results. But for all of them if i use graythresh then theresult not good for me. So any suggestions.

Answer 3

[ali]

Any suggestion, please