Rob, thank you very much for your quick reply.
Yes, that is exactly what I want, to measure the area all the way to the edge as one entire particle.
These small particles are a result of some bad lighting in the images or reflections and I don’t want to measure their areas. The original photo of the particle that I showed in my post (it is actually a droplet) is given below
I have tried filtering before but it is a lot of effort as some of the images have more small objects and therefore more unwanted measurements which will take some time to delete. Also, the measurement that I will be getting of the big particle will be less than what it actually is because of the small particles.
I have been trying your idea of playing with the circularity but because the circularity of the big particle is also changing and sometimes the circularity of the small particles is larger/smaller than the big particle, it is proving to be more tricky than I would have thought.
What I am doing now is selecting the area of the image where the unwanted small particles are and then going to edit/ fill, which is not a perfect approach but less daunting than the other option that I have had so far.
Any other suggestions are still welcome and appreciated.