Appropriate filter steps for resolving a droplet pixel I have a series of images obtained from a microscope as follows



I need to create a series of filters that would isolate the centre section    on the yellow droplet.(This is highlighted by the bright yellow circle area), and remove all the noise and other pictures.

I tried using just RGB  channel threshold but its not working. Also ambient light may also change so I am not getting a consistent output. Can anyone provide a MWE for the workflow of the filter required in MATLAB to achieve this?
First simple thresholding is usually not a good idea. However, if you want to do that, I suggest to also consider other color spaces. In your case, HSV might be a better choice; You can convert your image into HSV-image then you can define a range on Hue channel to select yellow.

Also, take a look at this article; it is about implementing Adaptive Thresholding.